mod(event): do not care about enum declarations

The union type can not be constructed with declarations anyway:
`error: reified unions must have no decls`; meaning there is no point in
even trying to do so.

.gitea/workflows/release.yaml

@@ -15,7 +15,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
       - name: Setup zig installation
-        uses: mlugg/setup-zig@v1
+        uses: mlugg/setup-zig@v2
         with:
           version: master
       - name: Run tests

.gitea/workflows/test.yaml

@@ -14,7 +14,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
       - name: Setup zig installation
-        uses: mlugg/setup-zig@v1
+        uses: mlugg/setup-zig@v2
         with:
           version: master
       - name: Lint check

README.md

@@ -2,7 +2,7 @@
 
 `zterm` is a terminal user interface library (*tui*) to implement terminal (fullscreen or inline) applications.
 
-> [!CAUTION]
+> [!caution]
 > Only builds using the zig master version are tested to work.
 
 ## Demo
@@ -13,7 +13,7 @@ Clone this repository and run `zig build --help` to see the available examples.
 zig build --release=safe -Dexample=demo run
 ```
 
-> [!TIP]
+> [!tip]
 > Every example application can be quit using `ctrl+c`.
 
 See the [wiki](https://gitea.yves-biener.de/yves-biener/zterm/wiki) for a showcase of the examples and the further details.

build.zig

@@ -1,5 +1,3 @@
-const std = @import("std");
-
 pub fn build(b: *std.Build) void {
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
@@ -7,10 +5,15 @@ pub fn build(b: *std.Build) void {
     const Examples = enum {
         all,
         demo,
+        continuous,
         // elements:
+        alignment,
         button,
         input,
+        progress,
+        radio_button,
         scrollable,
+        selection,
         // layouts:
         vertical,
         horizontal,
@@ -24,175 +27,81 @@ pub fn build(b: *std.Build) void {
     };
 
     const example = b.option(Examples, "example", "Example to build and/or run. (default: all)") orelse .all;
+    const debug_rendering = b.option(bool, "debug", "Enable debug rendering. Highlight origin's, size's, padding's, gap's, etc. (default: false)") orelse false;
+    // NOTE do not support debug rendering in release builds
+    if (debug_rendering == true and optimize != .Debug) @panic("Cannot enable debug rendering in non-debug builds.");
 
     const options = b.addOptions();
-    options.addOption(Examples, "example", example);
-
-    // dependencies
-    const zg = b.dependency("zg", .{
-        .target = target,
-        .optimize = optimize,
-    });
+    options.addOption(bool, "debug", debug_rendering);
+    const options_module = options.createModule();
 
     // library
     const lib = b.addModule("zterm", .{
-        .root_source_file = b.path("src/zterm.zig"),
+        .root_source_file = b.path("src/root.zig"),
         .target = target,
         .optimize = optimize,
+        .imports = &.{
+            .{ .name = "build_options", .module = options_module },
+        },
     });
-    lib.addImport("code_point", zg.module("code_point"));
 
     //--- Examples ---
-
-    // demo:
+    const examples = std.meta.fields(Examples);
+    inline for (examples) |e| {
+        if (@as(Examples, @enumFromInt(e.value)) == .all) continue; // skip `.all` entry
         const demo = b.addExecutable(.{
-        .name = "demo",
-        .root_source_file = b.path("examples/demo.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    demo.root_module.addImport("zterm", lib);
-
+            .name = e.name,
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(switch (@as(Examples, @enumFromInt(e.value))) {
+                    .demo => "examples/demo.zig",
+                    .continuous => "examples/continuous.zig",
                     // elements:
-    const button = b.addExecutable(.{
-        .name = "button",
-        .root_source_file = b.path("examples/elements/button.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    button.root_module.addImport("zterm", lib);
-
-    const input = b.addExecutable(.{
-        .name = "input",
-        .root_source_file = b.path("examples/elements/input.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    input.root_module.addImport("zterm", lib);
-
-    const scrollable = b.addExecutable(.{
-        .name = "scrollable",
-        .root_source_file = b.path("examples/elements/scrollable.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    scrollable.root_module.addImport("zterm", lib);
-
+                    .alignment => "examples/elements/alignment.zig",
+                    .button => "examples/elements/button.zig",
+                    .input => "examples/elements/input.zig",
+                    .progress => "examples/elements/progress.zig",
+                    .radio_button => "examples/elements/radio-button.zig",
+                    .scrollable => "examples/elements/scrollable.zig",
+                    .selection => "examples/elements/selection.zig",
                     // layouts:
-    const vertical = b.addExecutable(.{
-        .name = "vertical",
-        .root_source_file = b.path("examples/layouts/vertical.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    vertical.root_module.addImport("zterm", lib);
-
-    const horizontal = b.addExecutable(.{
-        .name = "horizontal",
-        .root_source_file = b.path("examples/layouts/horizontal.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    horizontal.root_module.addImport("zterm", lib);
-
-    const grid = b.addExecutable(.{
-        .name = "grid",
-        .root_source_file = b.path("examples/layouts/grid.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    grid.root_module.addImport("zterm", lib);
-
-    const mixed = b.addExecutable(.{
-        .name = "mixed",
-        .root_source_file = b.path("examples/layouts/mixed.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    mixed.root_module.addImport("zterm", lib);
-
+                    .vertical => "examples/layouts/vertical.zig",
+                    .horizontal => "examples/layouts/horizontal.zig",
+                    .grid => "examples/layouts/grid.zig",
+                    .mixed => "examples/layouts/mixed.zig",
                     // styles:
-    const palette = b.addExecutable(.{
-        .name = "palette",
-        .root_source_file = b.path("examples/styles/palette.zig"),
+                    .text => "examples/styles/text.zig",
+                    .palette => "examples/styles/palette.zig",
+                    // error handling
+                    .errors => "examples/errors.zig",
+                    .all => unreachable, // should never happen
+                }),
                 .target = target,
                 .optimize = optimize,
-    });
-    palette.root_module.addImport("zterm", lib);
-
-    const text = b.addExecutable(.{
-        .name = "text",
-        .root_source_file = b.path("examples/styles/text.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    text.root_module.addImport("zterm", lib);
-
-    // error handling:
-    const errors = b.addExecutable(.{
-        .name = "errors",
-        .root_source_file = b.path("examples/errors.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    errors.root_module.addImport("zterm", lib);
-
-    // mapping of user selected example to compile step
-    const exe = switch (example) {
-        .demo => demo,
-        // elements:
-        .button => button,
-        .input => input,
-        .scrollable => scrollable,
-        // layouts:
-        .vertical => vertical,
-        .horizontal => horizontal,
-        .grid => grid,
-        .mixed => mixed,
-        // styles:
-        .text => text,
-        .palette => palette,
-        // error handling:
-        .errors => errors,
-        else => blk: {
-            b.installArtifact(button);
-            b.installArtifact(input);
-            b.installArtifact(scrollable);
-            b.installArtifact(vertical);
-            b.installArtifact(horizontal);
-            b.installArtifact(grid);
-            b.installArtifact(mixed);
-            b.installArtifact(text);
-            b.installArtifact(palette);
-            b.installArtifact(errors);
-            break :blk demo;
+                .imports = &.{
+                    .{ .name = "zterm", .module = lib },
                 },
-    };
-    b.installArtifact(exe);
-
-    // zig build run
-    const run_cmd = b.addRunArtifact(exe);
-    run_cmd.step.dependOn(b.getInstallStep());
-    // Allow additional arguments, like this: `zig build run -- arg1 arg2 etc`
-    if (b.args) |args| run_cmd.addArgs(args);
-
-    // This creates a build step. It will be visible in the `zig build --help` menu,
-    // and can be selected like this: `zig build run`
-    // This will evaluate the `run` step rather than the default, which is "install".
-    const run_step = b.step("run", "Run the app");
-    run_step.dependOn(&run_cmd.step);
+            }),
+        });
+        // mapping of user selected example to compile step
+        if (@intFromEnum(example) == e.value or example == .all) b.installArtifact(demo);
+    }
 
     // zig build test
     const lib_unit_tests = b.addTest(.{
-        .root_source_file = b.path("src/zterm.zig"),
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/root.zig"),
             .target = target,
             .optimize = optimize,
+            .imports = &.{
+                .{ .name = "build_options", .module = options_module },
+            },
+        }),
     });
-    lib_unit_tests.root_module.addImport("code_point", zg.module("code_point"));
-    lib_unit_tests.root_module.addImport("DisplayWidth", zg.module("DisplayWidth"));
 
     const run_lib_unit_tests = b.addRunArtifact(lib_unit_tests);
 
     const test_step = b.step("test", "Run unit tests");
     test_step.dependOn(&run_lib_unit_tests.step);
 }
+
+const std = @import("std");

build.zig.zon

@@ -24,7 +24,7 @@
 
     // This is a [Semantic Version](https://semver.org/).
     // In a future version of Zig it will be used for package deduplication.
-    .version = "0.1.0",
+    .version = "0.3.0",
 
     // Tracks the earliest Zig version that the package considers to be a
     // supported use case.
@@ -35,12 +35,7 @@
     // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
     // Once all dependencies are fetched, `zig build` no longer requires
     // internet connectivity.
-    .dependencies = .{
-        .zg = .{
-            .url = "git+https://codeberg.org/atman/zg#4a002763419a34d61dcbb1f415821b83b9bf8ddc",
-            .hash = "1220f3e29bc40856bfc06e0ee133f814b0011c76de987d8a6a458c2f34d82708899a",
-        },
-    },
+    .dependencies = .{},
     .paths = .{
         "LICENSE",
         "build.zig",

examples/continuous.zig

@@ -0,0 +1,247 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+/// Spinner element implementation that runs a simple animation that requires
+/// the continuous draw loop.
+const Spinner = struct {
+    counter: u8 = 0,
+    index: u8 = 0,
+
+    const map: [6]u21 = .{ '𜺎', '𜺍', '𜺇', '𜹯', '𜹿', '𜺋' };
+
+    pub fn element(this: *@This()) App.Element {
+        return .{
+            .ptr = this,
+            .vtable = &.{
+                .content = content,
+            },
+        };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        const this: *@This() = @ptrCast(@alignCast(ctx));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        cells[size.x + 1].cp = map[this.index];
+
+        this.counter += 1;
+        if (this.counter >= 20) {
+            this.index += 1;
+            this.index %= 6;
+            this.counter = 0;
+        }
+    }
+};
+
+const InputField = struct {
+    allocator: std.mem.Allocator,
+    input: std.ArrayList(u21),
+    queue: *App.Queue,
+
+    pub fn init(allocator: std.mem.Allocator, queue: *App.Queue) @This() {
+        return .{
+            .allocator = allocator,
+            .input = std.ArrayList(u21).initCapacity(allocator, 8) catch unreachable,
+            .queue = queue,
+        };
+    }
+
+    pub fn deinit(this: *@This()) void {
+        this.input.deinit(this.allocator);
+    }
+
+    pub fn element(this: *@This()) App.Element {
+        return .{
+            .ptr = this,
+            .vtable = &.{
+                .handle = handle,
+                .content = content,
+            },
+        };
+    }
+
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
+        const this: *@This() = @ptrCast(@alignCast(ctx));
+        switch (event) {
+            .key => |key| {
+                if (key.isAscii()) try this.input.append(this.allocator, key.cp);
+
+                if (key.eql(.{ .cp = zterm.input.Enter }) or key.eql(.{ .cp = zterm.input.KpEnter }))
+                    this.queue.push(.{ .accept = try this.input.toOwnedSlice(this.allocator) });
+
+                if (key.eql(.{ .cp = zterm.input.Backspace }))
+                    _ = this.input.pop();
+
+                if (key.eql(.{ .cp = zterm.input.Delete }) or key.eql(.{ .cp = zterm.input.KpDelete }))
+                    _ = this.input.pop();
+            },
+            else => {},
+        }
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        const this: *@This() = @ptrCast(@alignCast(ctx));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        if (this.input.items.len == 0) return;
+
+        const row = 1;
+        const col = 1;
+        const anchor = (row * size.x) + col;
+
+        for (this.input.items, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .black;
+            cells[anchor + idx].style.cursor = false;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+
+            if (idx == this.input.items.len - 1) cells[anchor + idx + 1].style.cursor = true;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var input_field: InputField = .init(allocator, &app.queue);
+    defer input_field.deinit();
+
+    var quit_text: QuitText = .{};
+    var spinner: Spinner = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .grey },
+        .layout = .{
+            .direction = .vertical,
+            .padding = .all(5),
+        },
+    }, quit_text.element());
+    defer container.deinit();
+
+    try container.append(try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .light_grey },
+        .size = .{
+            .grow = .horizontal,
+            .dim = .{ .y = 10 },
+        },
+    }, input_field.element()));
+
+    const nested_container: App.Container = try .init(allocator, .{
+        .rectangle = .{ .fill = .light_grey },
+    }, spinner.element());
+    try container.append(nested_container);
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    var framerate: u64 = 60;
+    var tick_ms: u64 = @divFloor(time.ms_per_s, framerate);
+    var next_frame_ms: u64 = 0;
+
+    // draw loop
+    draw: while (true) {
+        const now_ms: u64 = @intCast(time.milliTimestamp());
+        if (now_ms >= next_frame_ms) {
+            next_frame_ms = now_ms + tick_ms;
+        } else {
+            std.Thread.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
+            next_frame_ms += tick_ms;
+        }
+
+        const len = blk: {
+            app.queue.lock();
+            defer app.queue.unlock();
+            break :blk app.queue.len();
+        };
+
+        // handle events
+        for (0..len) |_| {
+            const event = app.queue.drain() orelse break;
+            log.debug("handling event: {s}", .{@tagName(event)});
+            // pre event handling
+            switch (event) {
+                .key => |key| {
+                    log.debug("key {any}", .{key});
+                    if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit();
+                },
+                .accept => |input| {
+                    defer allocator.free(input);
+                    var string = try allocator.alloc(u8, input.len);
+                    defer allocator.free(string);
+                    for (0.., input) |i, char| string[i] = @intCast(char);
+                    log.debug("Accepted input '{s}'", .{string});
+                },
+                .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+                .focus => |b| {
+                    // NOTE reduce framerate in case the window is not focused and restore again when focused
+                    framerate = if (b) 60 else 15;
+                    tick_ms = @divFloor(time.ms_per_s, framerate);
+                },
+                else => {},
+            }
+
+            container.handle(&app.model, event) catch |err| app.postEvent(.{
+                .err = .{
+                    .err = err,
+                    .msg = "Container Event handling failed",
+                },
+            });
+
+            // post event handling
+            switch (event) {
+                .quit => break :draw,
+                else => {},
+            }
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const time = std.time;
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {
+    accept: []u21,
+});

examples/demo.zig

@@ -1,11 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const input = zterm.input;
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit. Press ctrl+n to launch helix.";
 
@@ -13,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    pub fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    pub fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const y = 2;
         const x = size.x / 2 -| (text.len / 2);
@@ -36,12 +28,12 @@ pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
     // TODO maybe create own allocator as some sort of arena allocator to have consistent memory usage
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -75,7 +67,7 @@ pub fn main() !void {
     }, .{}));
     defer box.deinit();
 
-    var scrollable: App.Scrollable = .{ .container = box };
+    var scrollable: App.Scrollable = .init(box, .disabled);
 
     var container = try App.Container.init(allocator, .{
         .layout = .{
@@ -87,15 +79,54 @@ pub fn main() !void {
     }, quit_text.element());
     try container.append(try App.Container.init(allocator, .{}, scrollable.element()));
 
-    try container.append(try App.Container.init(allocator, .{
+    var nested_container: App.Container = try .init(allocator, .{
+        .layout = .{
+            .direction = .vertical,
+            .separator = .{
+                .enabled = true,
+            },
+        },
+    }, .{});
+    var inner_container: App.Container = try .init(allocator, .{
+        .layout = .{
+            .direction = .vertical,
+        },
         .border = .{
             .color = .light_blue,
             .sides = .all,
         },
+    }, .{});
+    try inner_container.append(try .init(allocator, .{
+        .rectangle = .{
+            .fill = .blue,
+        },
         .size = .{
-            .dim = .{ .x = 100 },
+            .grow = .horizontal,
+            .dim = .{ .y = 5 },
         },
     }, .{}));
+    try inner_container.append(try .init(allocator, .{
+        .rectangle = .{
+            .fill = .red,
+        },
+        .size = .{
+            .grow = .horizontal,
+            .dim = .{ .y = 5 },
+        },
+    }, .{}));
+    try inner_container.append(try .init(allocator, .{
+        .rectangle = .{
+            .fill = .green,
+        },
+    }, .{}));
+    try nested_container.append(inner_container);
+    try nested_container.append(try .init(allocator, .{
+        .size = .{
+            .grow = .horizontal,
+            .dim = .{ .y = 1 },
+        },
+    }, .{}));
+    try container.append(nested_container);
     try container.append(try App.Container.init(allocator, .{
         .rectangle = .{ .fill = .blue },
         .size = .{
@@ -119,6 +150,7 @@ pub fn main() !void {
 
                 if (key.eql(.{ .cp = 'n', .mod = .{ .ctrl = true } })) {
                     try app.interrupt();
+                    renderer.size = .{}; // reset size, such that next resize will cause a full re-draw!
                     defer app.start() catch @panic("could not start app event loop");
                     var child = std.process.Child.init(&.{"hx"}, allocator);
                     _ = child.spawnAndWait() catch |err| app.postEvent(.{
@@ -136,7 +168,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -149,10 +181,18 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const input = zterm.input;
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/alignment.zig

@@ -0,0 +1,99 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var container: App.Container = try .init(allocator, .{}, .{});
+    defer container.deinit();
+
+    var quit_text: QuitText = .{};
+    const quit_container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .blue },
+        .layout = .{
+            .direction = .vertical,
+            .padding = .all(5),
+        },
+        .size = .{
+            .dim = .{ .x = 25, .y = 5 },
+            .grow = .fixed,
+        },
+    }, quit_text.element());
+
+    var alignment: App.Alignment = .init(quit_container, .center);
+    try container.append(try .init(allocator, .{}, alignment.element()));
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        // pre event handling
+        switch (event) {
+            .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
+            .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+            else => {},
+        }
+
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
+            .err = .{
+                .err = err,
+                .msg = "Container Event handling failed",
+            },
+        });
+
+        // post event handling
+        switch (event) {
+            .quit => break,
+            else => {},
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/button.zig

@@ -1,12 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {
-    click: [:0]const u8,
-});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -14,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -49,7 +40,7 @@ const Clickable = struct {
         };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
             .mouse => |mouse| if (mouse.button == .left and mouse.kind == .release) {
@@ -64,9 +55,9 @@ const Clickable = struct {
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = size.y / 2 -| (text.len / 2);
         const col = size.x / 2 -| (text.len / 2);
@@ -86,18 +77,20 @@ const Clickable = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
     var clickable: Clickable = .{ .queue = &app.queue };
     const element = clickable.element();
 
+    var button: App.Button(.accept) = .init(&app.queue, .init(.default, "Button"));
+
     var quit_text: QuitText = .{};
 
     var container = try App.Container.init(allocator, .{
@@ -107,6 +100,7 @@ pub fn main() !void {
     defer container.deinit();
 
     try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .light_grey } }, element));
+    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .black } }, button.element()));
 
     try app.start();
     defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
@@ -119,14 +113,13 @@ pub fn main() !void {
         // pre event handling
         switch (event) {
             .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
-            .click => |button| {
-                log.info("Clicked with mouse using Button: {s}", .{button});
-            },
+            .click => |b| log.info("Clicked with mouse using Button: {s}", .{b}),
+            .accept => log.info("Clicked built-in button using the mouse", .{}),
             .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -139,10 +132,23 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        click: [:0]const u8,
+        accept,
+    },
+);

examples/elements/input.zig

@@ -1,12 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {
-    accept: []u21,
-});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -14,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -33,20 +24,8 @@ const QuitText = struct {
     }
 };
 
-const InputField = struct {
-    input: std.ArrayList(u21),
-    queue: *App.Queue,
-
-    pub fn init(allocator: std.mem.Allocator, queue: *App.Queue) @This() {
-        return .{
-            .input = .init(allocator),
-            .queue = queue,
-        };
-    }
-
-    pub fn deinit(this: @This()) void {
-        this.input.deinit();
-    }
+const MouseDraw = struct {
+    position: ?zterm.Point = null,
 
     pub fn element(this: *@This()) App.Element {
         return .{
@@ -58,38 +37,22 @@ const InputField = struct {
         };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
-            .key => |key| {
-                if (key.isAscii()) try this.input.append(key.cp);
-
-                if (key.eql(.{ .cp = zterm.input.Enter }) or key.eql(.{ .cp = zterm.input.KpEnter }))
-                    this.queue.push(.{ .accept = try this.input.toOwnedSlice() });
-
-                if (key.eql(.{ .cp = zterm.input.Backspace }) or key.eql(.{ .cp = zterm.input.Delete }) or key.eql(.{ .cp = zterm.input.KpDelete }))
-                    _ = this.input.pop();
-            },
-            else => {},
+            .mouse => |mouse| this.position = .{ .x = mouse.x, .y = mouse.y },
+            else => this.position = null,
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
         const this: *@This() = @ptrCast(@alignCast(ctx));
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
-        if (this.input.items.len == 0) return;
-
-        const row = 1;
-        const col = 1;
-        const anchor = (row * size.x) + col;
-
-        for (this.input.items, 0..) |cp, idx| {
-            cells[anchor + idx].style.fg = .black;
-            cells[anchor + idx].cp = cp;
-
-            // NOTE do not write over the contents of this `Container`'s `Size`
-            if (anchor + idx == cells.len - 1) break;
+        if (this.position) |pos| {
+            const idx = @as(usize, size.x) * @as(usize, pos.y) + @as(usize, pos.x);
+            cells[idx].cp = 'x';
+            cells[idx].style.fg = .red;
         }
     }
 };
@@ -97,29 +60,59 @@ const InputField = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
-    var input_field: InputField = .init(allocator, &app.queue);
+    var input_field: App.Input(.accept) = .init(allocator, &app.queue, .init(.black));
     defer input_field.deinit();
 
+    var mouse_draw: MouseDraw = .{};
+    var second_mouse_draw: MouseDraw = .{};
     var quit_text: QuitText = .{};
 
-    const element = input_field.element();
-
     var container = try App.Container.init(allocator, .{
         .rectangle = .{ .fill = .grey },
-        .layout = .{ .padding = .all(5) },
+        .layout = .{
+            .direction = .vertical,
+            .padding = .all(5),
+        },
     }, quit_text.element());
     defer container.deinit();
 
-    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .light_grey } }, element));
+    try container.append(try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .light_grey },
+        .size = .{
+            .grow = .horizontal,
+            .dim = .{ .y = 1 },
+        },
+    }, input_field.element()));
+
+    var nested_container: App.Container = try .init(allocator, .{
+        .border = .{
+            .sides = .all,
+            .color = .black,
+        },
+        .rectangle = .{ .fill = .light_grey },
+        .layout = .{
+            .separator = .{
+                .enabled = true,
+                .color = .black,
+            },
+        },
+    }, .{});
+    try nested_container.append(try .init(allocator, .{
+        .rectangle = .{ .fill = .light_grey },
+    }, mouse_draw.element()));
+    try nested_container.append(try .init(allocator, .{
+        .rectangle = .{ .fill = .light_grey },
+    }, second_mouse_draw.element()));
+    try container.append(nested_container);
 
     try app.start();
     defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
@@ -134,13 +127,13 @@ pub fn main() !void {
             .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
             .accept => |input| {
                 defer allocator.free(input);
-                log.info("Accepted input {any}", .{input});
+                log.debug("Accepted input '{s}'", .{input});
             },
             .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -153,10 +146,24 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const Color = zterm.Color;
+
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        accept: []u8,
+    },
+);

examples/elements/progress.zig

@@ -0,0 +1,174 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var progress_percent: u8 = 0;
+    var quit_text: QuitText = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .layout = .{ .padding = .all(5), .direction = .vertical },
+    }, quit_text.element());
+    defer container.deinit();
+
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .left,
+            },
+            .fg = .blue,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .middle, // default
+            },
+            .fg = .red,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .right,
+            },
+            .fg = .green,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{ .enabled = false },
+            .fg = .default,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    var framerate: u64 = 60;
+    var tick_ms: u64 = @divFloor(time.ms_per_s, framerate);
+    var next_frame_ms: u64 = 0;
+
+    var increase_progress: u64 = 10;
+
+    // Continuous drawing
+    // draw loop
+    draw: while (true) {
+        const now_ms: u64 = @intCast(time.milliTimestamp());
+        if (now_ms >= next_frame_ms) {
+            next_frame_ms = now_ms + tick_ms;
+        } else {
+            std.Thread.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
+            next_frame_ms += tick_ms;
+        }
+
+        // NOTE time based progress increasion
+        increase_progress -= 1;
+        if (increase_progress == 0) {
+            increase_progress = 10;
+            progress_percent += 1;
+            if (progress_percent > 100) progress_percent = 0;
+            app.postEvent(.{ .progress = progress_percent });
+        }
+
+        const len = blk: {
+            app.queue.lock();
+            defer app.queue.unlock();
+            break :blk app.queue.len();
+        };
+
+        // handle events
+        for (0..len) |_| {
+            const event = app.queue.drain() orelse break;
+            log.debug("handling event: {s}", .{@tagName(event)});
+            // pre event handling
+            switch (event) {
+                .key => |key| {
+                    if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit();
+                },
+                .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+                .focus => |b| {
+                    // NOTE reduce framerate in case the window is not focused and restore again when focused
+                    framerate = if (b) 60 else 15;
+                    tick_ms = @divFloor(time.ms_per_s, framerate);
+                },
+                else => {},
+            }
+
+            container.handle(&app.model, event) catch |err| app.postEvent(.{
+                .err = .{
+                    .err = err,
+                    .msg = "Container Event handling failed",
+                },
+            });
+
+            // post event handling
+            switch (event) {
+                .quit => break :draw,
+                else => {},
+            }
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const time = std.time;
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        progress: u8,
+    },
+);

examples/elements/radio-button.zig

@@ -0,0 +1,98 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var radiobutton: App.RadioButton = .init(false, .{
+        .label = "Test Radio Button",
+        .style = .squared,
+    });
+    var button: App.Button(.accept) = .init(&app.queue, .init(.default, "Button"));
+    var quit_text: QuitText = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .grey },
+        .layout = .{ .padding = .all(5) },
+    }, quit_text.element());
+    defer container.deinit();
+    try container.append(try .init(allocator, .{}, radiobutton.element()));
+    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .black } }, button.element()));
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        // pre event handling
+        switch (event) {
+            .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
+            .accept => log.info("Clicked built-in button using the mouse", .{}),
+            .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+            else => {},
+        }
+
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
+            .err = .{
+                .err = err,
+                .msg = "Container Event handling failed",
+            },
+        });
+
+        // post event handling
+        switch (event) {
+            .quit => break,
+            else => {},
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {
+    accept,
+});

examples/elements/scrollable.zig

@@ -1,11 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const input = zterm.input;
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -13,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -42,9 +34,9 @@ const HelloWorldText = packed struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = size.y / 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -65,7 +57,7 @@ pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
     // TODO maybe create own allocator as some sort of arena allocator to have consistent memory usage
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer {
         const deinit_status = gpa.deinit();
         if (deinit_status == .leak) {
@@ -74,7 +66,7 @@ pub fn main() !void {
     }
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -156,10 +148,10 @@ pub fn main() !void {
     defer container.deinit();
 
     // place empty container containing the element of the scrollable Container.
-    var scrollable_top: App.Scrollable = .{ .container = top_box };
+    var scrollable_top: App.Scrollable = .init(top_box, .enabled(.grey));
     try container.append(try App.Container.init(allocator, .{}, scrollable_top.element()));
 
-    var scrollable_bottom: App.Scrollable = .{ .container = bottom_box };
+    var scrollable_bottom: App.Scrollable = .init(bottom_box, .enabled(.white));
     try container.append(try App.Container.init(allocator, .{}, scrollable_bottom.element()));
 
     try app.start();
@@ -177,7 +169,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -190,10 +182,18 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const input = zterm.input;
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/selection.zig

@@ -0,0 +1,97 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var selection: App.Selection(enum {
+        one,
+        two,
+        three,
+    }) = .init(.{
+        .label = "Selection",
+    });
+    var quit_text: QuitText = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .grey },
+        .layout = .{ .padding = .all(5) },
+    }, quit_text.element());
+    defer container.deinit();
+    try container.append(try .init(allocator, .{}, selection.element()));
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        // pre event handling
+        switch (event) {
+            .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
+            .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+            else => {},
+        }
+
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
+            .err = .{
+                .err = err,
+                .msg = "Container Event handling failed",
+            },
+        });
+
+        // post event handling
+        switch (event) {
+            .quit => break,
+            else => {},
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const Error = zterm.Error;
+const App = zterm.App(struct {}, union(enum) {});

examples/errors.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -12,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -38,9 +31,9 @@ const InfoText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -64,18 +57,18 @@ const ErrorNotification = struct {
         return .{ .ptr = this, .vtable = &.{ .handle = handle, .content = content } };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
-            .key => |key| if (!key.isAscii()) return error.UnsupportedKey,
+            .key => |key| if (!key.isAscii()) return zterm.Error.TooSmall,
             .err => |err| this.msg = err.msg,
             else => {},
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         if (this.msg) |msg| {
             const row = size.y -| 2;
@@ -99,12 +92,12 @@ const ErrorNotification = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -137,7 +130,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -150,10 +143,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/grid.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -15,9 +8,9 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -37,12 +30,12 @@ const QuitText = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -93,7 +86,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -106,10 +99,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/horizontal.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -15,9 +8,9 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -37,12 +30,12 @@ const QuitText = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -85,7 +78,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -98,10 +91,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/mixed.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -15,9 +8,9 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -37,12 +30,12 @@ const QuitText = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -101,7 +94,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -114,10 +107,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/vertical.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -15,9 +8,9 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -37,12 +30,12 @@ const QuitText = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -84,7 +77,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -97,10 +90,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/styles/palette.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -12,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -34,12 +27,12 @@ const QuitText = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -60,10 +53,10 @@ pub fn main() !void {
     defer box.deinit();
 
     inline for (std.meta.fields(zterm.Color)) |field| {
-        if (comptime field.value == 0) continue; // zterm.Color.default == 0 -> skip
+        if (field.value == 0) continue; // zterm.Color.default == 0 -> skip
         try box.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = @enumFromInt(field.value) } }, .{}));
     }
-    var scrollable: App.Scrollable = .{ .container = box };
+    var scrollable: App.Scrollable = .init(box, .disabled);
     try container.append(try App.Container.init(allocator, .{}, scrollable.element()));
 
     try app.start();
@@ -80,7 +73,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -93,10 +86,17 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {});

examples/styles/text.zig

@@ -1,10 +1,3 @@
-const std = @import("std");
-const zterm = @import("zterm");
-
-const App = zterm.App(union(enum) {});
-
-const log = std.log.scoped(.default);
-
 const QuitText = struct {
     const text = "Press ctrl+c to quit.";
 
@@ -12,9 +5,9 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         const row = 2;
         const col = size.x / 2 -| (text.len / 2);
@@ -35,24 +28,39 @@ const TextStyles = struct {
     const text = "Example";
 
     pub fn element(this: *@This()) App.Element {
-        return .{ .ptr = this, .vtable = &.{ .content = content } };
+        return .{
+            .ptr = this,
+            .vtable = &.{
+                .minSize = minSize,
+                .content = content,
+            },
+        };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
-        @setEvalBranchQuota(50000);
+    fn minSize(ctx: *anyopaque, size: zterm.Point) zterm.Point {
         _ = ctx;
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        _ = size;
+        return .{
+            .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
+            .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
+        };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        @setEvalBranchQuota(10000);
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         var row: usize = 0;
         var col: usize = 0;
 
         // Color
         inline for (std.meta.fields(zterm.Color)) |bg_field| {
-            if (comptime bg_field.value == 0) continue; // zterm.Color.default == 0 -> skip
+            if (bg_field.value == 0) continue; // zterm.Color.default == 0 -> skip
 
             inline for (std.meta.fields(zterm.Color)) |fg_field| {
-                if (comptime fg_field.value == 0) continue; // zterm.Color.default == 0 -> skip
-                if (comptime fg_field.value == bg_field.value) continue;
+                if (fg_field.value == 0) continue; // zterm.Color.default == 0 -> skip
+                if (fg_field.value == bg_field.value) continue;
 
                 // witouth any emphasis
                 for (text) |cp| {
@@ -64,7 +72,7 @@ const TextStyles = struct {
 
                 // emphasis (no combinations)
                 inline for (std.meta.fields(zterm.Style.Emphasis)) |emp_field| {
-                    if (comptime emp_field.value == 0) continue; // zterm.Style.Emphasis.reset == 0 -> skip
+                    if (emp_field.value == 0) continue; // zterm.Style.Emphasis.reset == 0 -> skip
                     const emphasis: zterm.Style.Emphasis = @enumFromInt(emp_field.value);
 
                     for (text) |cp| {
@@ -85,12 +93,12 @@ const TextStyles = struct {
 pub fn main() !void {
     errdefer |err| log.err("Application Error: {any}", .{err});
 
-    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
     defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -109,16 +117,10 @@ pub fn main() !void {
 
     var box = try App.Container.init(allocator, .{
         .layout = .{ .direction = .vertical },
-        .size = .{
-            .dim = .{
-                .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
-                .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
-            },
-        },
     }, text_styles.element());
     defer box.deinit();
 
-    var scrollable: App.Scrollable = .{ .container = box };
+    var scrollable: App.Scrollable = .init(box, .disabled);
     try container.append(try App.Container.init(allocator, .{}, scrollable.element()));
 
     try app.start();
@@ -135,7 +137,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -148,10 +150,18 @@ pub fn main() !void {
             else => {},
         }
 
-        try renderer.resize();
-        container.resize(renderer.size);
+        container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+
+const App = zterm.App(struct {}, union(enum) {});

src/app.zig

@@ -1,19 +1,4 @@
 //! Application type for TUI-applications
-const std = @import("std");
-const code_point = @import("code_point");
-const event = @import("event.zig");
-const input = @import("input.zig");
-const terminal = @import("terminal.zig");
-const queue = @import("queue.zig");
-
-const mergeTaggedUnions = event.mergeTaggedUnions;
-const isTaggedUnion = event.isTaggedUnion;
-
-const Mouse = input.Mouse;
-const Key = input.Key;
-const Point = @import("point.zig").Point;
-
-const log = std.log.scoped(.app);
 
 /// Create the App Type with the associated user events _E_ which describes
 /// an tagged union for all the user events that can be send through the
@@ -27,74 +12,69 @@ const log = std.log.scoped(.app);
 /// ```zig
 ///   const zterm = @import("zterm");
 ///   const App = zterm.App(
-///       union(enum) {},
+///       struct {}, // empty model
+///       union(enum) {}, // no additional user event's
 ///   );
 ///   // later on create an `App` instance and start the event loop
-///   var app: App = .init;
+///   var app: App = .init(.{}); // provide instance of the model that shall be used
 ///   try app.start();
-///   defer app.stop() catch unreachable;
+///   defer app.stop() catch unreachable; // does not clean-up the resources used in the model
 /// ```
-pub fn App(comptime E: type) type {
-    if (!isTaggedUnion(E)) {
-        @compileError("Provided user event `E` for `App(comptime E: type)` is not of type `union(enum)`.");
-    }
+pub fn App(comptime M: type, comptime E: type) type {
+    if (!isStruct(M)) @compileError("Provided model `M` for `App(comptime M: type, comptime E: type)` is not of type `struct`");
+    if (!isTaggedUnion(E)) @compileError("Provided user event `E` for `App(comptime M: type, comptime E: type)` is not of type `union(enum)`.");
     return struct {
-        pub const Event = mergeTaggedUnions(event.SystemEvent, E);
-        pub const Container = @import("container.zig").Container(Event);
-        const element = @import("element.zig");
-        pub const Element = element.Element(Event);
-        pub const Scrollable = element.Scrollable(Event);
-        pub const Queue = queue.Queue(Event, 256);
-
+        model: Model,
         queue: Queue,
-        thread: ?std.Thread,
-        quit_event: std.Thread.ResetEvent,
-        termios: ?std.posix.termios = null,
-        attached_handler: bool = false,
+        thread: ?Thread = null,
+        quit_event: Thread.ResetEvent,
+        termios: ?posix.termios = null,
+        winch_registered: bool = false,
 
-        pub const SignalHandler = struct {
-            context: *anyopaque,
-            callback: *const fn (context: *anyopaque) void,
-        };
+        // global variable for the registered handler for WINCH
+        var handler_ctx: *anyopaque = undefined;
+        /// registered WINCH handler to report resize events
+        fn handleWinch(_: std.os.linux.SIG) callconv(.c) void {
+            const this: *@This() = @ptrCast(@alignCast(handler_ctx));
+            // NOTE this does not have to be done if in-band resize events are supported
+            // -> the signal might not work correctly when hosting the application over ssh!
+            this.postEvent(.resize);
+        }
 
-        pub const init: @This() = .{
+        pub fn init(model: Model) @This() {
+            return .{
+                .model = model,
                 .queue = .{},
-            .thread = null,
-            .quit_event = .{},
-            .termios = null,
-            .attached_handler = false,
+                .quit_event = .unset,
             };
+        }
 
         pub fn start(this: *@This()) !void {
             if (this.thread) |_| return;
 
-            if (!this.attached_handler) {
-                var winch_act = std.posix.Sigaction{
-                    .handler = .{ .handler = @This().handleWinch },
-                    .mask = std.posix.empty_sigset,
-                    .flags = 0,
-                };
-                std.posix.sigaction(std.posix.SIG.WINCH, &winch_act, null);
-
-                try registerWinch(.{
-                    .context = this,
-                    .callback = @This().winsizeCallback,
-                });
-                this.attached_handler = true;
-
             // post init event (as the very first element to be in the queue - event loop)
             this.postEvent(.init);
+
+            if (!this.winch_registered) {
+                handler_ctx = this;
+                var act = posix.Sigaction{
+                    .handler = .{ .handler = handleWinch },
+                    .mask = posix.sigemptyset(),
+                    .flags = 0,
+                };
+                posix.sigaction(posix.SIG.WINCH, &act, null);
+                this.winch_registered = true;
             }
 
             this.quit_event.reset();
-            this.thread = try std.Thread.spawn(.{}, @This().run, .{this});
+            this.thread = try Thread.spawn(.{}, @This().run, .{this});
 
-            var termios: std.posix.termios = undefined;
+            var termios: posix.termios = undefined;
             try terminal.enableRawMode(&termios);
             if (this.termios) |_| {} else this.termios = termios;
 
-            try terminal.saveScreen();
             try terminal.enterAltScreen();
+            try terminal.saveScreen();
             try terminal.hideCursor();
             try terminal.enableMouseSupport();
         }
@@ -102,8 +82,8 @@ pub fn App(comptime E: type) type {
         pub fn interrupt(this: *@This()) !void {
             this.quit_event.set();
             try terminal.disableMouseSupport();
-            try terminal.exitAltScreen();
             try terminal.restoreScreen();
+            try terminal.exitAltScreen();
             if (this.thread) |thread| {
                 thread.join();
                 this.thread = null;
@@ -112,12 +92,12 @@ pub fn App(comptime E: type) type {
 
         pub fn stop(this: *@This()) !void {
             try this.interrupt();
-            if (this.termios) |*termios| {
+            if (this.termios) |termios| {
                 try terminal.disableMouseSupport();
                 try terminal.showCursor();
-                try terminal.exitAltScreen();
-                try terminal.disableRawMode(termios);
                 try terminal.restoreScreen();
+                try terminal.disableRawMode(&termios);
+                try terminal.exitAltScreen();
             }
             this.termios = null;
         }
@@ -139,27 +119,6 @@ pub fn App(comptime E: type) type {
             this.queue.push(e);
         }
 
-        fn winsizeCallback(ptr: *anyopaque) void {
-            const this: *@This() = @ptrCast(@alignCast(ptr));
-            _ = this;
-            // this.postEvent(.{ .size = terminal.getTerminalSize() });
-        }
-
-        var winch_handler: ?SignalHandler = null;
-
-        fn registerWinch(handler: SignalHandler) !void {
-            if (winch_handler) |_| {
-                @panic("Cannot register another WINCH handler.");
-            }
-            winch_handler = handler;
-        }
-
-        fn handleWinch(_: c_int) callconv(.C) void {
-            if (winch_handler) |handler| {
-                handler.callback(handler.context);
-            }
-        }
-
         fn run(this: *@This()) !void {
             // thread to read user inputs
             var buf: [256]u8 = undefined;
@@ -208,6 +167,9 @@ pub fn App(comptime E: type) type {
                                         // Legacy keys
                                         // CSI {ABCDEFHPQS}
                                         // CSI 1 ; modifier:event_type {ABCDEFHPQS}
+                                        var field_iter = std.mem.splitScalar(u8, sequence[2 .. sequence.len - 1], ';');
+                                        _ = field_iter.next(); // skip first field
+
                                         const key: Key = .{
                                             .cp = switch (final) {
                                                 'A' => input.Up,
@@ -221,22 +183,36 @@ pub fn App(comptime E: type) type {
                                                 'Q' => input.F2,
                                                 'R' => input.F3,
                                                 'S' => input.F4,
-                                                else => unreachable, // switch case prevents in this case form ever happening
+                                                else => unreachable,
+                                            },
+                                            .mod = blk: {
+                                                // modifier_mask:event_type
+                                                var mod: Key.Modifier = .{};
+                                                const field_buf = field_iter.next() orelse break :blk mod;
+                                                var param_iter = std.mem.splitScalar(u8, field_buf, ':');
+                                                const modifier_buf = param_iter.next() orelse unreachable;
+                                                const modifier_mask = fmt.parseUnsigned(u8, modifier_buf, 10) catch break :blk mod;
+                                                if ((modifier_mask -| 1) & 1 != 0) mod.shift = true;
+                                                if ((modifier_mask -| 1) & 2 != 0) mod.alt = true;
+                                                if ((modifier_mask -| 1) & 4 != 0) mod.ctrl = true;
+                                                break :blk mod;
                                             },
                                         };
                                         this.postEvent(.{ .key = key });
                                     },
+                                    'Z' => this.postEvent(.{ .key = .{ .cp = input.Tab, .mod = .{ .shift = true } } }),
                                     '~' => {
                                         // Legacy keys
                                         // CSI number ~
                                         // CSI number ; modifier ~
                                         // CSI number ; modifier:event_type ; text_as_codepoint ~
-                                        var field_iter = std.mem.splitScalar(u8, sequence[2 .. sequence.len - 1], ';');
-                                        const number_buf = field_iter.next() orelse unreachable; // always will have one field
-                                        const number = std.fmt.parseUnsigned(u16, number_buf, 10) catch break;
+                                        var field_iter = mem.splitScalar(u8, sequence[2 .. sequence.len - 1], ';');
 
                                         const key: Key = .{
-                                            .cp = switch (number) {
+                                            .cp = blk: {
+                                                const number_buf = field_iter.next() orelse unreachable; // always will have one field
+                                                const number = fmt.parseUnsigned(u16, number_buf, 10) catch break;
+                                                break :blk switch (number) {
                                                     2 => input.Insert,
                                                     3 => input.Delete,
                                                     5 => input.PageUp,
@@ -255,10 +231,31 @@ pub fn App(comptime E: type) type {
                                                     21 => input.F10,
                                                     23 => input.F11,
                                                     24 => input.F12,
+                                                    25 => input.F13,
+                                                    26 => input.F14,
+                                                    28 => input.F15,
+                                                    29 => input.F16,
+                                                    31 => input.F17,
+                                                    32 => input.F18,
+                                                    33 => input.F19,
+                                                    34 => input.F20,
                                                     // 200 => return .{ .event = .paste_start, .n = sequence.len },
                                                     // 201 => return .{ .event = .paste_end, .n = sequence.len },
-                                                57427 => input.KpBegin,
+                                                    57399...57454 => |code| code,
                                                     else => unreachable,
+                                                };
+                                            },
+                                            .mod = blk: {
+                                                // modifier_mask:event_type
+                                                var mod: Key.Modifier = .{};
+                                                const field_buf = field_iter.next() orelse break :blk mod;
+                                                var param_iter = std.mem.splitScalar(u8, field_buf, ':');
+                                                const modifier_buf = param_iter.next() orelse unreachable;
+                                                const modifier_mask = fmt.parseUnsigned(u8, modifier_buf, 10) catch break :blk mod;
+                                                if ((modifier_mask -| 1) & 1 != 0) mod.shift = true;
+                                                if ((modifier_mask -| 1) & 2 != 0) mod.alt = true;
+                                                if ((modifier_mask -| 1) & 4 != 0) mod.ctrl = true;
+                                                break :blk mod;
                                             },
                                         };
                                         this.postEvent(.{ .key = key });
@@ -267,14 +264,14 @@ pub fn App(comptime E: type) type {
                                     'I' => this.postEvent(.{ .focus = true }),
                                     'O' => this.postEvent(.{ .focus = false }),
                                     'M', 'm' => {
-                                        std.debug.assert(sequence.len >= 4);
+                                        assert(sequence.len >= 4);
                                         if (sequence[2] != '<') break;
 
-                                        const delim1 = std.mem.indexOfScalarPos(u8, sequence, 3, ';') orelse break;
-                                        const button_mask = std.fmt.parseUnsigned(u16, sequence[3..delim1], 10) catch break;
-                                        const delim2 = std.mem.indexOfScalarPos(u8, sequence, delim1 + 1, ';') orelse break;
-                                        const px = std.fmt.parseUnsigned(u16, sequence[delim1 + 1 .. delim2], 10) catch break;
-                                        const py = std.fmt.parseUnsigned(u16, sequence[delim2 + 1 .. sequence.len - 1], 10) catch break;
+                                        const delim1 = mem.indexOfScalarPos(u8, sequence, 3, ';') orelse break;
+                                        const button_mask = fmt.parseUnsigned(u16, sequence[3..delim1], 10) catch break;
+                                        const delim2 = mem.indexOfScalarPos(u8, sequence, delim1 + 1, ';') orelse break;
+                                        const px = fmt.parseUnsigned(u16, sequence[delim1 + 1 .. delim2], 10) catch break;
+                                        const py = fmt.parseUnsigned(u16, sequence[delim2 + 1 .. sequence.len - 1], 10) catch break;
 
                                         const mouse_bits = packed struct {
                                             const motion: u8 = 0b00100000;
@@ -295,12 +292,8 @@ pub fn App(comptime E: type) type {
                                             .x = px -| 1,
                                             .y = py -| 1,
                                             .kind = blk: {
-                                                if (motion and button != Mouse.Button.none) {
-                                                    break :blk .drag;
-                                                }
-                                                if (motion and button == Mouse.Button.none) {
-                                                    break :blk .motion;
-                                                }
+                                                if (motion and button != Mouse.Button.none) break :blk .drag;
+                                                if (motion and button == Mouse.Button.none) break :blk .motion;
                                                 if (sequence[sequence.len - 1] == 'm') break :blk .release;
                                                 break :blk .press;
                                             },
@@ -314,14 +307,14 @@ pub fn App(comptime E: type) type {
                                         // Device Status Report
                                         // CSI Ps n
                                         // CSI ? Ps n
-                                        std.debug.assert(sequence.len >= 3);
+                                        assert(sequence.len >= 3);
                                     },
                                     't' => {
                                         // XTWINOPS
                                         // Split first into fields delimited by ';'
-                                        var iter = std.mem.splitScalar(u8, sequence[2 .. sequence.len - 1], ';');
+                                        var iter = mem.splitScalar(u8, sequence[2 .. sequence.len - 1], ';');
                                         const ps = iter.first();
-                                        if (std.mem.eql(u8, "48", ps)) {
+                                        if (mem.eql(u8, "48", ps)) {
                                             // in band window resize
                                             // CSI 48 ; height ; width ; height_pix ; width_pix t
                                             const width_char = iter.next() orelse break;
@@ -329,9 +322,10 @@ pub fn App(comptime E: type) type {
 
                                             _ = width_char;
                                             _ = height_char;
+                                            this.postEvent(.resize);
                                             // this.postEvent(.{ .size = .{
-                                            //     .x = std.fmt.parseUnsigned(u16, width_char, 10) catch break,
-                                            //     .y = std.fmt.parseUnsigned(u16, height_char, 10) catch break,
+                                            //     .x = fmt.parseUnsigned(u16, width_char, 10) catch break,
+                                            //     .y = fmt.parseUnsigned(u16, height_char, 10) catch break,
                                             // } });
                                         }
                                     },
@@ -347,9 +341,29 @@ pub fn App(comptime E: type) type {
                                     else => {},
                                 }
                             },
+                            0x50 => {
+                                // DCS
+                            },
+                            0x58 => {
+                                // SOS
+                            },
+                            0x5D => {
+                                // OSC
+                            },
                             // TODO parse corresponding codes
-                            // 0x5B => parseCsi(input, &self.buf), // CSI see https://github.com/rockorager/libvaxis/blob/main/src/Parser.zig
-                            else => {},
+                            0x5F => {
+                                // APC
+                                // parse for kitty graphics capabilities
+                            },
+                            else => {
+                                // alt + <char> keypress
+                                this.postEvent(.{
+                                    .key = .{
+                                        .cp = buf[1],
+                                        .mod = .{ .alt = true },
+                                    },
+                                });
+                            },
                         }
                     } else {
                         const b = buf[0];
@@ -357,16 +371,17 @@ pub fn App(comptime E: type) type {
                             0x00 => .{ .cp = '@', .mod = .{ .ctrl = true } },
                             0x08 => .{ .cp = input.Backspace },
                             0x09 => .{ .cp = input.Tab },
-                            0x0a, 0x0d => .{ .cp = input.Enter },
+                            0x0a => .{ .cp = 'j', .mod = .{ .ctrl = true } },
+                            0x0d => .{ .cp = input.Enter },
                             0x01...0x07, 0x0b...0x0c, 0x0e...0x1a => .{ .cp = b + 0x60, .mod = .{ .ctrl = true } },
                             0x1b => escape: {
-                                std.debug.assert(read_bytes == 1);
+                                assert(read_bytes == 1);
                                 break :escape .{ .cp = input.Escape };
                             },
                             0x7f => .{ .cp = input.Backspace },
                             else => {
-                                var iter = code_point.Iterator{ .bytes = buf[0..read_bytes] };
-                                while (iter.next()) |cp| this.postEvent(.{ .key = .{ .cp = cp.code } });
+                                var iter: std.unicode.Utf8Iterator = .{ .bytes = buf[0..read_bytes], .i = 0 };
+                                while (iter.nextCodepoint()) |cp| this.postEvent(.{ .key = .{ .cp = cp } });
                                 continue;
                             },
                         };
@@ -377,5 +392,56 @@ pub fn App(comptime E: type) type {
                 break;
             }
         }
+
+        pub fn panic_handler(msg: []const u8, _: ?*std.builtin.StackTrace, ret_addr: ?usize) noreturn {
+            terminal.disableMouseSupport() catch {};
+            terminal.showCursor() catch {};
+            terminal.restoreScreen() catch {};
+            terminal.disableRawMode(&.{
+                .iflag = .{},
+                .lflag = .{},
+                .cflag = .{},
+                .oflag = .{},
+                .cc = undefined,
+                .line = 0,
+                .ispeed = undefined,
+                .ospeed = undefined,
+            }) catch {};
+            terminal.exitAltScreen() catch {};
+            std.debug.defaultPanic(msg, ret_addr);
+        }
+
+        const element = @import("element.zig");
+        pub const Model = M;
+        pub const Event = mergeTaggedUnions(event.SystemEvent, E);
+        pub const Container = @import("container.zig").Container(Model, Event);
+        pub const Element = element.Element(Model, Event);
+        pub const Alignment = element.Alignment(Model, Event);
+        pub const Button = element.Button(Model, Event, Queue);
+        pub const Input = element.Input(Model, Event, Queue);
+        pub const Progress = element.Progress(Model, Event, Queue);
+        pub const RadioButton = element.RadioButton(Model, Event);
+        pub const Scrollable = element.Scrollable(Model, Event);
+        pub const Selection = element.Selection(Model, Event);
+        pub const Queue = queue.Queue(Event, 256);
     };
 }
+
+const log = std.log.scoped(.app);
+
+const std = @import("std");
+const mem = std.mem;
+const fmt = std.fmt;
+const posix = std.posix;
+const Thread = std.Thread;
+const assert = std.debug.assert;
+const event = @import("event.zig");
+const input = @import("input.zig");
+const terminal = @import("terminal.zig");
+const queue = @import("queue.zig");
+const mergeTaggedUnions = event.mergeTaggedUnions;
+const isTaggedUnion = event.isTaggedUnion;
+const isStruct = event.isStruct;
+const Mouse = input.Mouse;
+const Key = input.Key;
+const Point = @import("point.zig").Point;

src/cell.zig

@@ -1,11 +1,8 @@
-const std = @import("std");
-const Style = @import("style.zig");
+//! Cell type containing content and formatting for each character in the terminal screen.
 
-pub const Cell = @This();
-
-style: Style = .{ .emphasis = &.{} },
 // TODO embrace `zg` dependency more due to utf-8 encoding
 cp: u21 = ' ',
+style: Style = .{ .emphasis = &.{} },
 
 pub fn eql(this: Cell, other: Cell) bool {
     return this.cp == other.cp and this.style.eql(other.style);
@@ -16,10 +13,14 @@ pub fn reset(this: *Cell) void {
     this.cp = ' ';
 }
 
-pub fn value(this: Cell, writer: anytype) !void {
+pub fn value(this: Cell, writer: *std.Io.Writer) !void {
     try this.style.value(writer, this.cp);
 }
 
+const std = @import("std");
+const Style = @import("style.zig");
+const Cell = @This();
+
 test "ascii styled text" {
     const cells: [4]Cell = .{
         .{ .cp = 'Y', .style = .{ .fg = .green, .bg = .grey, .emphasis = &.{} } },
@@ -28,17 +29,15 @@ test "ascii styled text" {
         .{ .cp = 's', .style = .{ .fg = .light_green, .bg = .black, .emphasis = &.{.underline} } },
     };
 
-    var string = std.ArrayList(u8).init(std.testing.allocator);
-    defer string.deinit();
-
-    const writer = string.writer();
+    var writer = std.Io.Writer.Allocating.init(std.testing.allocator);
+    defer writer.deinit();
     for (cells) |cell| {
-        try cell.value(writer);
+        try cell.value(&writer.writer);
     }
     try std.testing.expectEqualSlices(
         u8,
         "\x1b[38;5;10;48;5;8;59mY\x1b[0m\x1b[39;49;59;1;4mv\x1b[0m\x1b[39;49;59;3me\x1b[0m\x1b[38;5;2;48;5;16;59;4ms\x1b[0m",
-        string.items,
+        writer.writer.buffer[0..writer.writer.end],
     );
 }
 
@@ -50,16 +49,14 @@ test "utf-8 styled text" {
         .{ .cp = '┘', .style = .{ .fg = .light_green, .bg = .black, .emphasis = &.{.underline} } },
     };
 
-    var string = std.ArrayList(u8).init(std.testing.allocator);
-    defer string.deinit();
-
-    const writer = string.writer();
+    var writer = std.Io.Writer.Allocating.init(std.testing.allocator);
+    defer writer.deinit();
     for (cells) |cell| {
-        try cell.value(writer);
+        try cell.value(&writer.writer);
     }
     try std.testing.expectEqualSlices(
         u8,
         "\x1b[38;5;10;48;5;8;59m╭\x1b[0m\x1b[39;49;59m─\x1b[0m\x1b[39;49;59m┄\x1b[0m\x1b[38;5;2;48;5;16;59;4m┘\x1b[0m",
-        string.items,
+        writer.writer.buffer[0..writer.writer.end],
     );
 }

src/color.zig

@@ -1,5 +1,3 @@
-const std = @import("std");
-
 pub const Color = enum(u8) {
     default = 0,
     black = 16,
@@ -20,19 +18,23 @@ pub const Color = enum(u8) {
     white,
     // TODO add further colors as described in https://gist.github.com/ConnerWill/d4b6c776b509add763e17f9f113fd25b # Color / Graphics Mode - 256 Colors
 
-    pub inline fn write(this: Color, writer: anytype, comptime coloring: enum { fg, bg, ul }) !void {
+    // TODO might be useful to use the std.ascii stuff!
+
+    pub inline fn write(this: Color, writer: *std.Io.Writer, comptime coloring: enum { fg, bg, ul }) !void {
         if (this == .default) {
             switch (coloring) {
-                .fg => try std.fmt.format(writer, "39", .{}),
-                .bg => try std.fmt.format(writer, "49", .{}),
-                .ul => try std.fmt.format(writer, "59", .{}),
+                .fg => try writer.printAscii("39", .{}),
+                .bg => try writer.printAscii("49", .{}),
+                .ul => try writer.printAscii("59", .{}),
             }
         } else {
             switch (coloring) {
-                .fg => try std.fmt.format(writer, "38;5;{d}", .{@intFromEnum(this)}),
-                .bg => try std.fmt.format(writer, "48;5;{d}", .{@intFromEnum(this)}),
-                .ul => try std.fmt.format(writer, "58;5;{d}", .{@intFromEnum(this)}),
+                .fg => try writer.print("38;5;{d}", .{@intFromEnum(this)}),
+                .bg => try writer.print("48;5;{d}", .{@intFromEnum(this)}),
+                .ul => try writer.print("58;5;{d}", .{@intFromEnum(this)}),
             }
         }
     }
 };
+
+const std = @import("std");

src/container.zig

@@ -1,21 +1,8 @@
-const std = @import("std");
-
-const isTaggedUnion = @import("event.zig").isTaggedUnion;
-
-const Cell = @import("cell.zig");
-const Color = @import("color.zig").Color;
-const Point = @import("point.zig").Point;
-const Style = @import("style.zig");
-const Error = @import("error.zig").Error;
-
-const log = std.log.scoped(.container);
+// FIX known issues:
+// - hold fewer instances of the `Allocator`
 
 /// Border configuration struct
 pub const Border = packed struct {
-    // corners:
-    const rounded_border: [6]u21 = .{ '╭', '─', '╮', '│', '╰', '╯' };
-    const squared_border: [6]u21 = .{ '┌', '─', '┐', '│', '└', '┘' };
-
     /// Color to use for the border
     color: Color = .default,
     /// Configure the corner type to be used for the border
@@ -39,13 +26,12 @@ pub const Border = packed struct {
     } = .{},
 
     pub fn content(this: @This(), cells: []Cell, size: Point) void {
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
-        const frame = switch (this.corners) {
-            .rounded => Border.rounded_border,
-            .squared => Border.squared_border,
+        const frame: [6]u21 = switch (this.corners) {
+            .rounded => .{ '╭', '─', '╮', '│', '╰', '╯' },
+            .squared => .{ '┌', '─', '┐', '│', '└', '┘' },
         };
-        std.debug.assert(frame.len == 6);
 
         // render top and bottom border
         if (this.sides.top or this.sides.bottom) {
@@ -94,8 +80,9 @@ pub const Border = packed struct {
     test "all sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .all,
@@ -106,14 +93,15 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.all.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.all.zon"));
     }
 
     test "vertical sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .vertical,
@@ -124,14 +112,15 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.vertical.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.vertical.zon"));
     }
 
     test "horizontal sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .horizontal,
@@ -142,7 +131,7 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.horizontal.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.horizontal.zon"));
     }
 };
 
@@ -155,20 +144,28 @@ pub const Rectangle = packed struct {
 
     // NOTE caller owns `Cells` slice and ensures that `cells.len == size.x * size.y`
     pub fn content(this: @This(), cells: []Cell, size: Point) void {
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         for (0..size.y) |row| {
             for (0..size.x) |col| {
                 cells[(row * size.x) + col].style.bg = this.fill;
             }
         }
+
+        // DEBUG render corresponding beginning of the rectangle for this `Container` *red*
+        if (comptime build_options.debug) {
+            cells[0].style.fg = .red;
+            cells[0].style.bg = .black;
+            cells[0].cp = 'r'; // 'r' for *rectangle*
+        }
     }
 
     test "fill color overwrite parent fill" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{ .fill = .green },
         }, .{});
         try container.append(try .init(std.testing.allocator, .{
@@ -180,14 +177,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_parent_fill_without_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_fill_without_padding.zon"));
     }
 
     test "fill color padding to show parent fill" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .padding = .all(2),
             },
@@ -202,14 +200,43 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_parent_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_padding.zon"));
+    }
+
+    test "fill color padding to show parent fill (negative padding)" {
+        const event = @import("event.zig");
+        const testing = @import("testing.zig");
+        const Model = struct {};
+
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
+            .layout = .{
+                .padding = .{
+                    .top = -18,
+                    .bottom = -18,
+                    .left = -28,
+                    .right = -28,
+                },
+            },
+            .rectangle = .{ .fill = .green },
+        }, .{});
+        try container.append(try .init(std.testing.allocator, .{
+            .rectangle = .{ .fill = .white },
+        }, .{}));
+        try container.append(try .init(std.testing.allocator, .{}, .{}));
+        defer container.deinit();
+
+        try testing.expectContainerScreen(.{
+            .y = 20,
+            .x = 30,
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_padding.zon"));
     }
 
     test "fill color spacer with padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -230,14 +257,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_padding.zon"));
     }
 
     test "fill color with gap" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -261,14 +289,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_gap.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_gap.zon"));
     }
 
     test "fill color with separator" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -293,38 +322,33 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_separator.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_separator.zon"));
     }
 };
 
 /// Layout configuration struct
 pub const Layout = packed struct {
-    // separator.line:
-    const line: [2]u21 = .{ '│', '─' };
-    const dotted: [2]u21 = .{ '┆', '┄' };
-    const double: [2]u21 = .{ '║', '═' };
-
     /// control the direction in which child elements are laid out
     direction: enum(u1) { horizontal, vertical } = .horizontal,
     /// Padding outside of the child elements
     padding: packed struct {
-        top: u16 = 0,
-        bottom: u16 = 0,
-        left: u16 = 0,
-        right: u16 = 0,
+        top: i16 = 0,
+        bottom: i16 = 0,
+        left: i16 = 0,
+        right: i16 = 0,
 
         /// Create a padding with equivalent padding in all four directions.
-        pub fn all(padding: u16) @This() {
+        pub fn all(padding: i16) @This() {
             return .{ .top = padding, .bottom = padding, .left = padding, .right = padding };
         }
 
         /// Create a padding with equivalent padding in the left and right directions; others directions remain the default value.
-        pub fn horizontal(padding: u16) @This() {
+        pub fn horizontal(padding: i16) @This() {
             return .{ .left = padding, .right = padding };
         }
 
         /// Create a padding with equivalent padding in the top and bottom directions; others directions remain the default value.
-        pub fn vertical(padding: u16) @This() {
+        pub fn vertical(padding: i16) @This() {
             return .{ .top = padding, .bottom = padding };
         }
     } = .{},
@@ -341,14 +365,19 @@ pub const Layout = packed struct {
         } = .line,
     } = .{},
 
+    /// Calculate the absolute offset for the provided `padding` if it is negative to get the absolute padding for the given `size`.
+    pub fn getAbsolutePadding(padding: i16, size: u16) u16 {
+        return if (padding >= 0) @intCast(padding) else size -| @as(u16, @intCast(-padding));
+    }
+
     pub fn content(this: @This(), comptime C: type, cells: []Cell, origin: Point, size: Point, children: []const C) void {
-        std.debug.assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
         if (this.separator.enabled and children.len > 1) {
             const line_cps: [2]u21 = switch (this.separator.line) {
-                .line => line,
-                .dotted => dotted,
-                .double => double,
+                .line => .{ '│', '─' },
+                .dotted => .{ '┆', '┄' },
+                .double => .{ '║', '═' },
             };
             const gap: u16 = (this.gap + 1) / 2;
 
@@ -371,8 +400,11 @@ pub const Layout = packed struct {
                 }
 
                 // DEBUG render corresponding beginning of the separator for this `Container` *red*
-                // cells[anchor].style.fg = .red;
-                // cells[anchor].style.bg = .red;
+                if (comptime build_options.debug) {
+                    cells[anchor].style.fg = .red;
+                    cells[anchor].style.bg = .black;
+                    cells[anchor].cp = 's'; // 's' for *separator*
+                }
             }
         }
     }
@@ -380,8 +412,9 @@ pub const Layout = packed struct {
     test "separator without gaps" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .separator = .{
                     .enabled = true,
@@ -395,14 +428,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_no_gaps.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_no_gaps.zon"));
     }
 
     test "separator without gaps with padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .padding = .all(1),
                 .separator = .{
@@ -417,14 +451,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_no_gaps_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_no_gaps_with_padding.zon"));
     }
 
     test "separator(2x) without gaps" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .direction = .vertical,
                 .separator = .{
@@ -441,14 +476,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps.zon"));
     }
 
     test "separator(2x) with border(all)" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -468,14 +504,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps_with_border.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps_with_border.zon"));
     }
 
     test "separator(2x) with border(all) and padding(all(1))" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -496,14 +533,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps_with_padding.zon"));
     }
 
     test "separator(2x) with border(all) and gap" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -524,14 +562,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_with_gaps_with_border.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_with_gaps_with_border.zon"));
     }
 
     test "separator(2x) with border(all) and gap and padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -553,7 +592,7 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_with_gaps_with_border_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_with_gaps_with_border_with_padding.zon"));
     }
 };
 
@@ -568,16 +607,17 @@ pub const Size = packed struct {
     } = .both,
 };
 
-pub fn Container(comptime Event: type) type {
+pub fn Container(Model: type, Event: type) type {
     if (!isTaggedUnion(Event)) @compileError("Provided user event `Event` for `Container(comptime Event: type)`");
 
-    const Element = @import("element.zig").Element(Event);
+    const Element = @import("element.zig").Element(Model, Event);
     return struct {
-        allocator: std.mem.Allocator,
+        allocator: Allocator,
         origin: Point,
         size: Point,
         properties: Properties,
         element: Element,
+        // TODO this should be renamed to `children`
         elements: std.ArrayList(@This()),
 
         /// Properties for each `Container` to configure their layout,
@@ -591,7 +631,7 @@ pub fn Container(comptime Event: type) type {
         };
 
         pub fn init(
-            allocator: std.mem.Allocator,
+            allocator: Allocator,
             properties: Properties,
             element: Element,
         ) !@This() {
@@ -601,19 +641,17 @@ pub fn Container(comptime Event: type) type {
                 .size = .{},
                 .properties = properties,
                 .element = element,
-                .elements = std.ArrayList(@This()).init(allocator),
+                .elements = try std.ArrayList(@This()).initCapacity(allocator, 2),
             };
         }
 
         pub fn deinit(this: *@This()) void {
-            for (this.elements.items) |*element| {
-                element.deinit();
-            }
-            this.elements.deinit();
+            for (this.elements.items) |*element| element.deinit();
+            this.elements.deinit(this.allocator);
         }
 
         pub fn append(this: *@This(), element: @This()) !void {
-            try this.elements.append(element);
+            try this.elements.append(this.allocator, element);
         }
 
         pub fn reposition(this: *@This(), origin: Point) void {
@@ -622,8 +660,8 @@ pub fn Container(comptime Event: type) type {
             this.element.reposition(origin);
 
             var offset = origin.add(.{
-                .x = layout.padding.left,
-                .y = layout.padding.top,
+                .x = Layout.getAbsolutePadding(layout.padding.left, this.size.x),
+                .y = Layout.getAbsolutePadding(layout.padding.top, this.size.y),
             });
 
             const sides = this.properties.border.sides;
@@ -655,8 +693,8 @@ pub fn Container(comptime Event: type) type {
             };
 
             if (this.elements.items.len > 0) switch (layout.direction) {
-                .horizontal => size.x += layout.padding.left + layout.padding.right,
-                .vertical => size.y += layout.padding.top + layout.padding.bottom,
+                .horizontal => size.x += Layout.getAbsolutePadding(layout.padding.left, this.size.x) + Layout.getAbsolutePadding(layout.padding.right, this.size.x),
+                .vertical => size.y += Layout.getAbsolutePadding(layout.padding.top, this.size.y) + Layout.getAbsolutePadding(layout.padding.bottom, this.size.y),
             };
 
             const sides = this.properties.border.sides;
@@ -697,25 +735,23 @@ pub fn Container(comptime Event: type) type {
                     .y = @max(size.y, this.properties.size.dim.y),
                 },
             };
-            log.debug("fit_size returning: {any}", .{this.size});
             return this.size;
         }
 
         /// growable implicitly requires the root `Container` to have a set a size property to the size of the available terminal screen
         fn grow_resize(this: *@This(), max_size: Point) void {
-            log.debug("grow_size: {any}", .{this.size});
             const layout = this.properties.layout;
             var remainder = switch (layout.direction) {
-                .horizontal => max_size.x -| (layout.padding.left + layout.padding.right),
-                .vertical => max_size.y -| (layout.padding.top + layout.padding.bottom),
+                .horizontal => max_size.x -| (Layout.getAbsolutePadding(layout.padding.left, this.size.x) + Layout.getAbsolutePadding(layout.padding.right, this.size.x)),
+                .vertical => max_size.y -| (Layout.getAbsolutePadding(layout.padding.top, this.size.y) + Layout.getAbsolutePadding(layout.padding.bottom, this.size.y)),
             };
             remainder -|= layout.gap * @as(u16, @truncate(this.elements.items.len -| 1));
 
             if (layout.separator.enabled) remainder -|= @as(u16, @truncate(this.elements.items.len -| 1));
 
             var available = switch (layout.direction) {
-                .horizontal => max_size.y -| (layout.padding.top + layout.padding.bottom),
-                .vertical => max_size.x -| (layout.padding.left + layout.padding.right),
+                .horizontal => max_size.y -| (Layout.getAbsolutePadding(layout.padding.top, this.size.y) + Layout.getAbsolutePadding(layout.padding.bottom, this.size.y)),
+                .vertical => max_size.x -| (Layout.getAbsolutePadding(layout.padding.left, this.size.x) + Layout.getAbsolutePadding(layout.padding.right, this.size.x)),
             };
 
             const sides = this.properties.border.sides;
@@ -788,6 +824,11 @@ pub fn Container(comptime Event: type) type {
                 for (this.elements.items) |child| {
                     if (child.properties.size.grow == .fixed) continue;
 
+                    switch (layout.direction) {
+                        .horizontal => if (child.properties.size.grow == .vertical) continue,
+                        .vertical => if (child.properties.size.grow == .horizontal) continue,
+                    }
+
                     const size = switch (layout.direction) {
                         .horizontal => child.size.x,
                         .vertical => child.size.y,
@@ -804,10 +845,8 @@ pub fn Container(comptime Event: type) type {
 
                 size_to_correct = @min(size_to_correct, remainder / growable_children);
                 var overflow: u16 = 0;
-                if (size_to_correct == 0 and remainder > 0) {
-                    // there is some overflow
-                    overflow = remainder;
-                }
+                if (size_to_correct == 0 and remainder > 0) overflow = remainder;
+
                 for (this.elements.items) |*child| {
                     const child_size = switch (layout.direction) {
                         .horizontal => child.size.x,
@@ -817,9 +856,11 @@ pub fn Container(comptime Event: type) type {
                         switch (layout.direction) {
                             .horizontal => if (child.properties.size.grow != .vertical) {
                                 child.size.x += size_to_correct;
+                                remainder -|= size_to_correct;
                             },
                             .vertical => if (child.properties.size.grow != .horizontal) {
                                 child.size.y += size_to_correct;
+                                remainder -|= size_to_correct;
                             },
                         }
                         if (overflow > 0) {
@@ -836,7 +877,6 @@ pub fn Container(comptime Event: type) type {
                                 },
                             }
                         }
-                        remainder -|= size_to_correct;
                     }
                 }
             }
@@ -847,6 +887,7 @@ pub fn Container(comptime Event: type) type {
 
         pub fn resize(this: *@This(), size: Point) void {
             // NOTE assume that this function is only called for the root `Container`
+            this.size = size;
             const fit_size = this.fit_resize();
             // if (fit_size.y > size.y or fit_size.x > size.x) @panic("error: cannot render in available space");
             switch (this.properties.size.grow) {
@@ -864,51 +905,79 @@ pub fn Container(comptime Event: type) type {
             this.grow_resize(this.size);
         }
 
-        pub fn handle(this: *@This(), event: Event) !void {
+        pub fn handle(this: *const @This(), model: *Model, event: Event) !void {
             switch (event) {
                 .mouse => |mouse| if (mouse.in(this.origin, this.size)) {
-                    try this.element.handle(event);
-                    for (this.elements.items) |*element| try element.handle(event);
-                },
-                else => {
-                    try this.element.handle(event);
-                    for (this.elements.items) |*element| try element.handle(event);
+                    // the element receives the mouse event with relative position
+                    assert(mouse.x >= this.origin.x and mouse.y >= this.origin.y);
+                    var relative_mouse: input.Mouse = mouse;
+                    relative_mouse.x -= this.origin.x;
+                    relative_mouse.y -= this.origin.y;
+                    try this.element.handle(model, .{ .mouse = relative_mouse });
                 },
+                else => try this.element.handle(model, event),
             }
+            for (this.elements.items) |*element| try element.handle(model, event);
         }
 
-        pub fn content(this: *const @This()) ![]const Cell {
+        pub fn content(this: *const @This(), model: *const Model) ![]Cell {
             if (this.size.x == 0 or this.size.y == 0) return Error.TooSmall;
+
             const cells = try this.allocator.alloc(Cell, @as(usize, this.size.x) * @as(usize, this.size.y));
-            @memset(cells, .{});
             errdefer this.allocator.free(cells);
+            @memset(cells, .{});
 
             this.properties.layout.content(@This(), cells, this.origin, this.size, this.elements.items);
             this.properties.border.content(cells, this.size);
             this.properties.rectangle.content(cells, this.size);
 
-            try this.element.content(cells, this.size);
+            try this.element.content(model, cells, this.size);
 
-            // DEBUG render corresponding top left corner of this `Container` *red*
-            // cells[0].style.fg = .red;
-            // cells[0].style.bg = .red;
+            // DEBUG render corresponding corners (except top left) of this `Container` *red*
+            if (comptime build_options.debug) {
+                // top right
+                cells[this.size.x -| 1].style.fg = .red;
+                cells[this.size.x -| 1].style.bg = .black;
+                cells[this.size.x -| 1].cp = 'c'; // 'c' for *container*
+                // bottom left
+                cells[this.size.x * (this.size.y -| 1)].style.fg = .red;
+                cells[this.size.x * (this.size.y -| 1)].style.bg = .black;
+                cells[this.size.x * (this.size.y -| 1)].cp = 'c'; // 'c' for *container*
+                // bottom right
+                cells[this.size.x * this.size.y -| 1].style.fg = .red;
+                cells[this.size.x * this.size.y -| 1].style.bg = .black;
+                cells[this.size.x * this.size.y -| 1].cp = 'c'; // 'c' for *container*
+            }
 
             return cells;
         }
     };
 }
 
+const log = std.log.scoped(.container);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const build_options = @import("build_options");
+const input = @import("input.zig");
+const isTaggedUnion = @import("event.zig").isTaggedUnion;
+const Cell = @import("cell.zig");
+const Color = @import("color.zig").Color;
+const Point = @import("point.zig").Point;
+const Style = @import("style.zig");
+const Error = @import("error.zig").Error;
+
 test {
-    _ = Border;
-    _ = Layout;
-    _ = Rectangle;
+    @import("std").testing.refAllDeclsRecursive(@This());
 }
 
 test "Container Fixed and Grow Size Vertical" {
     const event = @import("event.zig");
     const testing = @import("testing.zig");
+    const Model = struct {};
 
-    var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+    var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
         .layout = .{ .direction = .vertical },
     }, .{});
     try container.append(try .init(std.testing.allocator, .{
@@ -926,14 +995,15 @@ test "Container Fixed and Grow Size Vertical" {
     try testing.expectContainerScreen(.{
         .y = 20,
         .x = 30,
-    }, &container, @import("test/container/fixed_grow_vertical.zon"));
+    }, @TypeOf(container), &container, Model, @import("test/container/fixed_grow_vertical.zon"));
 }
 
 test "Container Fixed and Grow Size Horizontal" {
     const event = @import("event.zig");
     const testing = @import("testing.zig");
+    const Model = struct {};
 
-    var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{}, .{});
+    var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{}, .{});
     try container.append(try .init(std.testing.allocator, .{
         .size = .{
             .dim = .{ .x = 5 },
@@ -949,5 +1019,5 @@ test "Container Fixed and Grow Size Horizontal" {
     try testing.expectContainerScreen(.{
         .y = 20,
         .x = 30,
-    }, &container, @import("test/container/fixed_grow_horizontal.zon"));
+    }, @TypeOf(container), &container, Model, @import("test/container/fixed_grow_horizontal.zon"));
 }

src/event.zig

@@ -1,12 +1,5 @@
 //! Events which are defined by the library. They might be extended by user
 //! events. See `App` for more details about user defined events.
-const std = @import("std");
-const input = @import("input.zig");
-const terminal = @import("terminal.zig");
-
-const Key = input.Key;
-const Mouse = input.Mouse;
-const Point = @import("point.zig").Point;
 
 /// System events available to every `zterm.App`
 pub const SystemEvent = union(enum) {
@@ -15,8 +8,11 @@ pub const SystemEvent = union(enum) {
     init,
     /// Quit event to signify the end of the event loop (rendering should stop afterwards)
     quit,
+    /// Resize event to signify that the application should re-draw to resize
+    resize,
     /// Error event to notify other containers about a recoverable error
     err: struct {
+        /// actual error
         err: anyerror,
         /// associated error message
         msg: []const u8,
@@ -25,15 +21,19 @@ pub const SystemEvent = union(enum) {
     key: Key,
     /// Mouse input event
     mouse: Mouse,
-    /// Focus event for mouse interaction
-    /// TODO this should instead be a union with a `Size` to derive which container / element the focus meant for
+    /// Focus event indicating that the application has gained the focus of the user
     focus: bool,
 };
 
+/// Merge the two provided `union(enum)` `A` and `B` to a tagged union containing all fields of both tagged unions in `comptime`.
+/// Declarations are not supported for `comptime` created types, see https://github.com/ziglang/zig/issues/6709 for details.
 pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
-    if (!isTaggedUnion(A) or !isTaggedUnion(B)) {
-        @compileError("Both types for merging tagged unions need to be of type `union(enum)`.");
-    }
+    // TODO maybe it makes sense to have a nested tagged union type (i.e. system: union(enum) and event: union(enum))
+    // - allows re-definition of system / built-in events
+    // - clearly shows which events are system / built-in ones and which are user defined events
+    // - the memory footprint for the nesting is not really harmful
+    if (!isTaggedUnion(A) or !isTaggedUnion(B)) @compileError("Both types for merging tagged unions need to be of type `union(enum)`.");
+
     const a_fields = @typeInfo(A).@"union".fields;
     const a_fields_tag = @typeInfo(A).@"union".tag_type.?;
     const a_enum_fields = @typeInfo(a_fields_tag).@"enum".fields;
@@ -58,11 +58,27 @@ pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
         i += 1;
     }
 
-    const log2_i = @bitSizeOf(@TypeOf(i)) - @clz(i);
+    // NOTE declarations are not supported for `comptime` types: https://github.com/ziglang/zig/issues/6709
+    // -> will lead to a compilation error when constructing the tagged union
+    //    at the end of this function in case at least one of the provided tagged
+    //    unions to merge contains declarations (which in this case can only be the
+    //    user provided one)
+    const a_enum_decls = @typeInfo(A).@"union".decls;
+    const b_enum_decls = @typeInfo(B).@"union".decls;
+    var decls: [a_enum_decls.len + b_enum_decls.len]std.builtin.Type.Declaration = undefined;
+    var j: usize = 0;
+    for (a_enum_decls) |decl| {
+        decls[j] = decl;
+        j += 1;
+    }
+    for (b_enum_decls) |decl| {
+        decls[j] = decl;
+        j += 1;
+    }
 
     const EventType = @Type(.{ .int = .{
         .signedness = .unsigned,
-        .bits = log2_i,
+        .bits = @bitSizeOf(@TypeOf(i)) - @clz(i),
     } });
 
     const Event = @Type(.{ .@"enum" = .{
@@ -80,15 +96,28 @@ pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
     } });
 }
 
-// Determine at `comptime` whether the provided type `E` is an `union(enum)`.
-pub fn isTaggedUnion(comptime E: type) bool {
-    switch (@typeInfo(E)) {
-        .@"union" => |u| {
-            if (u.tag_type) |_| {} else {
+/// Determine whether the provided type `T` is a tagged union: `union(enum)`.
+pub fn isTaggedUnion(comptime T: type) bool {
+    switch (@typeInfo(T)) {
+        .@"union" => |u| if (u.tag_type) |_| {} else {
             return false;
-            }
         },
         else => return false,
     }
     return true;
 }
+
+/// Determine whether the provided type `T` is a `struct`.
+pub fn isStruct(comptime T: type) bool {
+    return switch (@typeInfo(T)) {
+        .@"struct" => |_| true,
+        else => false,
+    };
+}
+
+const std = @import("std");
+const input = @import("input.zig");
+const terminal = @import("terminal.zig");
+const Key = input.Key;
+const Mouse = input.Mouse;
+const Point = @import("point.zig").Point;

src/input.zig

@@ -1,7 +1,4 @@
 //! Input module for `zterm`. Contains structs to represent key events and mouse events.
-const std = @import("std");
-
-const Point = @import("point.zig").Point;
 
 pub const Mouse = packed struct {
     x: u16,
@@ -32,7 +29,7 @@ pub const Mouse = packed struct {
     };
 
     pub fn eql(this: @This(), other: @This()) bool {
-        return std.meta.eql(this, other);
+        return meta.eql(this, other);
     }
 
     pub fn in(this: @This(), origin: Point, size: Point) bool {
@@ -65,9 +62,11 @@ pub const Key = packed struct {
     /// }
     /// ```
     pub fn eql(this: @This(), other: @This()) bool {
-        return std.meta.eql(this, other);
+        return meta.eql(this, other);
     }
 
+    // TODO might be useful to use the std.ascii stuff!
+
     /// Determine if the `Key` is an ascii character that can be printed to
     /// the screen. This means that the code point of the `Key` is an ascii
     /// character between 32 - 255 (with the exception of 127 = Delete) and no
@@ -90,24 +89,25 @@ pub const Key = packed struct {
     }
 
     test "isAscii with ascii character" {
-        try std.testing.expectEqual(true, isAscii(.{ .cp = 'c' }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .ctrl = true } }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .alt = true } }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .alt = true, .ctrl = true } }));
+        try testing.expectEqual(true, isAscii(.{ .cp = 'c' }));
+        try testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .ctrl = true } }));
+        try testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .alt = true } }));
+        try testing.expectEqual(false, isAscii(.{ .cp = 'c', .mod = .{ .alt = true, .ctrl = true } }));
     }
 
     test "isAscii with non-ascii character" {
-        try std.testing.expectEqual(false, isAscii(.{ .cp = Escape }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = Enter }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = Enter, .mod = .{ .alt = true } }));
+        try testing.expectEqual(false, isAscii(.{ .cp = Escape }));
+        try testing.expectEqual(false, isAscii(.{ .cp = Enter }));
+        try testing.expectEqual(false, isAscii(.{ .cp = Enter, .mod = .{ .alt = true } }));
     }
 
     test "isAscii with excluded input.Delete" {
-        try std.testing.expectEqual(false, isAscii(.{ .cp = Delete }));
-        try std.testing.expectEqual(false, isAscii(.{ .cp = Delete, .mod = .{ .alt = false, .ctrl = false } }));
+        try testing.expectEqual(false, isAscii(.{ .cp = Delete }));
+        try testing.expectEqual(false, isAscii(.{ .cp = Delete, .mod = .{ .alt = false, .ctrl = false } }));
     }
 };
 
+// TODO: std.ascii has the escape codes too!
 // codepoints for keys
 pub const Tab: u21 = 0x09;
 pub const Enter: u21 = 0x0D;
@@ -152,21 +152,6 @@ pub const F17: u21 = 57380;
 pub const F18: u21 = 57381;
 pub const F19: u21 = 57382;
 pub const F20: u21 = 57383;
-pub const F21: u21 = 57384;
-pub const F22: u21 = 57385;
-pub const F23: u21 = 57386;
-pub const F24: u21 = 57387;
-pub const F25: u21 = 57388;
-pub const F26: u21 = 57389;
-pub const F27: u21 = 57390;
-pub const F28: u21 = 57391;
-pub const F29: u21 = 57392;
-pub const F30: u21 = 57393;
-pub const F31: u21 = 57394;
-pub const F32: u21 = 57395;
-pub const F33: u21 = 57396;
-pub const F34: u21 = 57397;
-pub const F35: u21 = 57398;
 pub const Kp0: u21 = 57399;
 pub const Kp1: u21 = 57400;
 pub const Kp2: u21 = 57401;
@@ -223,3 +208,8 @@ pub const RightHyper: u21 = 57451;
 pub const RightMeta: u21 = 57452;
 pub const IsoLevel3Shift: u21 = 57453;
 pub const IsoLevel5Shift: u21 = 57454;
+
+const std = @import("std");
+const meta = std.meta;
+const Point = @import("point.zig").Point;
+const testing = std.testing;

src/queue.zig

@@ -1,9 +1,7 @@
 // taken from https://github.com/rockorager/libvaxis/blob/main/src/queue.zig (MIT-License)
 // with slight modifications
-const std = @import("std");
-const assert = std.debug.assert;
 
-/// Thread safe. Fixed size. Blocking push and pop.
+/// Queue implementation. Thread safe. Fixed size. Blocking push and pop. Polling through tryPop and tryPush.
 pub fn Queue(comptime T: type, comptime size: usize) type {
     return struct {
         buf: [size]T = undefined,
@@ -92,6 +90,23 @@ pub fn Queue(comptime T: type, comptime size: usize) type {
             assert(!this.isEmptyLH());
         }
 
+        pub fn lock(this: *QueueType) void {
+            this.mutex.lock();
+        }
+
+        pub fn unlock(this: *QueueType) void {
+            this.mutex.unlock();
+        }
+
+        /// Used to efficiently drain the queue
+        pub fn drain(this: *QueueType) ?T {
+            if (this.isEmptyLH()) return null;
+
+            const result = this.buf[this.mask(this.read_index)];
+            this.read_index = this.mask2(this.read_index + 1);
+            return result;
+        }
+
         fn isEmptyLH(this: QueueType) bool {
             return this.write_index == this.read_index;
         }
@@ -116,7 +131,7 @@ pub fn Queue(comptime T: type, comptime size: usize) type {
         }
 
         /// Returns the length
-        fn len(this: QueueType) usize {
+        pub fn len(this: QueueType) usize {
             const wrap_offset = 2 * this.buf.len *
                 @intFromBool(this.write_index < this.read_index);
             const adjusted_write_index = this.write_index + wrap_offset;
@@ -135,8 +150,12 @@ pub fn Queue(comptime T: type, comptime size: usize) type {
     };
 }
 
+const std = @import("std");
 const testing = std.testing;
+const assert = std.debug.assert;
+const Thread = std.Thread;
 const cfg = Thread.SpawnConfig{ .allocator = testing.allocator };
+
 test "Queue: simple push / pop" {
     var queue: Queue(u8, 16) = .{};
     queue.push(1);
@@ -146,7 +165,6 @@ test "Queue: simple push / pop" {
     try testing.expectEqual(2, queue.pop());
 }
 
-const Thread = std.Thread;
 fn testPushPop(q: *Queue(u8, 2)) !void {
     q.push(3);
     try testing.expectEqual(2, q.pop());
@@ -197,9 +215,9 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
     // still full and the push in the other thread is still blocked
     // waiting for space.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s);
+    std.Thread.sleep(std.time.ns_per_s);
     // Finally, let that other thread go.
-    try std.testing.expectEqual(1, q.pop());
+    try testing.expectEqual(1, q.pop());
 
     // This won't continue until the other thread has had a chance to
     // put at least one item in the queue.
@@ -207,7 +225,7 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
         try Thread.yield();
     // But we want to ensure that there's a second push waiting, so
     // here's another sleep.
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Another spurious wake...
     q.not_full.signal();
@@ -215,10 +233,10 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
     // And another chance for the other thread to see that it's
     // spurious and go back to sleep.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Pop that thing and we're done.
-    try std.testing.expectEqual(2, q.pop());
+    try testing.expectEqual(2, q.pop());
 }
 
 test "Fill, block, fill, block" {
@@ -238,28 +256,28 @@ test "Fill, block, fill, block" {
 
     // Just to make sure the sleeps are yielding to this thread, make
     // sure it took at least 900ms to do the push.
-    try std.testing.expect(then - now > 900);
+    try testing.expect(then - now > 900);
 
     // This should block again, waiting for the other thread.
     queue.push(4);
 
     // And once that push has gone through, the other thread's done.
     thread.join();
-    try std.testing.expectEqual(3, queue.pop());
-    try std.testing.expectEqual(4, queue.pop());
+    try testing.expectEqual(3, queue.pop());
+    try testing.expectEqual(4, queue.pop());
 }
 
 fn sleepyPush(q: *Queue(u8, 1)) !void {
     // Try to ensure the other thread has already started trying to pop.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Spurious wake
     q.not_full.signal();
     q.not_empty.signal();
 
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Stick something in the queue so it can be popped.
     q.push(1);
@@ -268,7 +286,7 @@ fn sleepyPush(q: *Queue(u8, 1)) !void {
         try Thread.yield();
     // Give the other thread time to block again.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Spurious wake
     q.not_full.signal();
@@ -284,8 +302,8 @@ test "Drain, block, drain, block" {
 
     var queue: Queue(u8, 1) = .{};
     const thread = try Thread.spawn(cfg, sleepyPush, .{&queue});
-    try std.testing.expectEqual(1, queue.pop());
-    try std.testing.expectEqual(2, queue.pop());
+    try testing.expectEqual(1, queue.pop());
+    try testing.expectEqual(2, queue.pop());
     thread.join();
 }
 
@@ -299,7 +317,7 @@ test "2 readers" {
     const t1 = try Thread.spawn(cfg, readerThread, .{&queue});
     const t2 = try Thread.spawn(cfg, readerThread, .{&queue});
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
     queue.push(1);
     queue.push(1);
     t1.join();

src/render.zig

@@ -1,18 +1,14 @@
-const std = @import("std");
-const terminal = @import("terminal.zig");
-
-const Cell = @import("cell.zig");
-const Point = @import("point.zig").Point;
+//! Renderer for `zterm`.
 
 /// Double-buffered intermediate rendering pipeline
 pub const Buffered = struct {
-    allocator: std.mem.Allocator,
+    allocator: Allocator,
     created: bool,
     size: Point,
     screen: []Cell,
     virtual_screen: []Cell,
 
-    pub fn init(allocator: std.mem.Allocator) @This() {
+    pub fn init(allocator: Allocator) @This() {
         return .{
             .allocator = allocator,
             .created = false,
@@ -29,9 +25,9 @@ pub const Buffered = struct {
         }
     }
 
-    pub fn resize(this: *@This()) !void {
+    pub fn resize(this: *@This()) !Point {
         const size = terminal.getTerminalSize();
-        if (std.meta.eql(this.size, size)) return;
+        if (meta.eql(this.size, size)) return this.size;
 
         this.size = size;
         const n = @as(usize, this.size.x) * @as(usize, this.size.y);
@@ -52,6 +48,7 @@ pub const Buffered = struct {
             @memset(this.virtual_screen, .{});
         }
         try this.clear();
+        return size;
     }
 
     /// Clear the entire screen and reset the screen buffer, to force a re-draw with the next `flush` call.
@@ -61,10 +58,10 @@ pub const Buffered = struct {
     }
 
     /// Render provided cells at size (anchor and dimension) into the *virtual screen*.
-    pub fn render(this: *@This(), comptime T: type, container: *T) !void {
+    pub fn render(this: *@This(), comptime Container: type, container: *Container, comptime Model: type, model: *const Model) !void {
         const size: Point = container.size;
         const origin: Point = container.origin;
-        const cells: []const Cell = try container.content();
+        const cells: []const Cell = try container.content(model);
 
         if (cells.len == 0) return;
 
@@ -83,13 +80,15 @@ pub const Buffered = struct {
         // free immediately
         container.allocator.free(cells);
 
-        for (container.elements.items) |*element| try this.render(T, element);
+        for (container.elements.items) |*element| try this.render(Container, element, Model, model);
     }
 
     /// Write *virtual screen* to alternate screen (should be called once and last during each render loop iteration in the main loop).
     pub fn flush(this: *@This()) !void {
+        try terminal.hideCursor();
         // TODO measure timings of rendered frames?
-        const writer = terminal.writer();
+        var cursor_position: ?Point = null;
+        var writer = terminal.writer();
         const s = this.screen;
         const vs = this.virtual_screen;
         for (0..this.size.y) |row| {
@@ -97,14 +96,36 @@ pub const Buffered = struct {
                 const idx = (row * this.size.x) + col;
                 const cs = s[idx];
                 const cvs = vs[idx];
+
+                // update the latest found cursor position
+                if (cvs.style.cursor) {
+                    assert(cursor_position == null);
+                    cursor_position = .{
+                        .x = @truncate(col),
+                        .y = @truncate(row),
+                    };
+                }
+
                 if (cs.eql(cvs)) continue;
 
                 // render differences found in virtual screen
-                try terminal.setCursorPosition(.{ .y = @truncate(row + 1), .x = @truncate(col + 1) });
-                try cvs.value(writer);
+                try terminal.setCursorPosition(.{ .y = @truncate(row), .x = @truncate(col) });
+                try cvs.value(&writer);
                 // update screen to be the virtual screen for the next frame
                 s[idx] = vs[idx];
             }
         }
+        if (cursor_position) |point| {
+            try terminal.showCursor();
+            try terminal.setCursorPosition(point);
+        }
     }
 };
+
+const std = @import("std");
+const meta = std.meta;
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const terminal = @import("terminal.zig");
+const Cell = @import("cell.zig");
+const Point = @import("point.zig").Point;

src/root.zig

@@ -17,7 +17,6 @@ pub const Renderer = @import("render.zig");
 // Container Configurations
 pub const Border = container.Border;
 pub const Rectangle = container.Rectangle;
-pub const Scroll = container.Scroll;
 pub const Layout = container.Layout;
 
 pub const Cell = @import("cell.zig");

src/style.zig

@@ -7,11 +7,13 @@
 
 // taken from https://github.com/rockorager/libvaxis/blob/main/src/Cell.zig (MIT-License)
 // with slight modifications
-const std = @import("std");
 
-const Color = @import("color.zig").Color;
-
-pub const Style = @This();
+fg: Color = .default,
+bg: Color = .default,
+ul: Color = .default,
+cursor: bool = false,
+ul_style: Underline = .off,
+emphasis: []const Emphasis,
 
 pub const Underline = enum {
     off,
@@ -34,39 +36,42 @@ pub const Emphasis = enum(u8) {
     strikethrough,
 };
 
-fg: Color = .default,
-bg: Color = .default,
-ul: Color = .default,
-ul_style: Underline = .off,
-emphasis: []const Emphasis,
-
 pub fn eql(this: Style, other: Style) bool {
-    return std.meta.eql(this, other);
+    return meta.eql(this, other);
 }
 
-pub fn value(this: Style, writer: anytype, cp: u21) !void {
+// TODO might be useful to use the std.ascii stuff!
+
+pub fn value(this: Style, writer: *std.Io.Writer, cp: u21) !void {
     var buffer: [4]u8 = undefined;
-    const bytes = try std.unicode.utf8Encode(cp, &buffer);
-    std.debug.assert(bytes > 0);
+    const bytes = try unicode.utf8Encode(cp, &buffer);
+    assert(bytes > 0);
     // build ansi sequence for 256 colors ...
     // foreground
-    try std.fmt.format(writer, "\x1b[", .{});
+    try writer.printAscii("\x1b[", .{});
     try this.fg.write(writer, .fg);
     // background
-    try std.fmt.format(writer, ";", .{});
+    try writer.printAsciiChar(';', .{});
     try this.bg.write(writer, .bg);
     // underline
     // FIX assert that if the underline property is set that the ul style and the attribute for underlining is available
-    try std.fmt.format(writer, ";", .{});
+    try writer.printAsciiChar(';', .{});
     try this.ul.write(writer, .ul);
     // append styles (aka attributes like bold, italic, strikethrough, etc.)
-    for (this.emphasis) |attribute| try std.fmt.format(writer, ";{d}", .{@intFromEnum(attribute)});
-    try std.fmt.format(writer, "m", .{});
+    for (this.emphasis) |attribute| try writer.print(";{d}", .{@intFromEnum(attribute)});
+    try writer.printAsciiChar('m', .{});
     // content
-    try std.fmt.format(writer, "{s}", .{buffer[0..bytes]});
-    try std.fmt.format(writer, "\x1b[0m", .{});
+    try writer.printAscii(buffer[0..bytes], .{});
+    try writer.printAscii("\x1b[0m", .{});
 }
 
 // TODO implement helper functions for terminal capabilities:
 // - links / url display (osc 8)
 // - show / hide cursor?
+
+const std = @import("std");
+const unicode = std.unicode;
+const meta = std.meta;
+const assert = std.debug.assert;
+const Color = @import("color.zig").Color;
+const Style = @This();

src/terminal.zig

@@ -1,15 +1,3 @@
-const std = @import("std");
-const code_point = @import("code_point");
-const ctlseqs = @import("ctlseqs.zig");
-const input = @import("input.zig");
-
-const Key = input.Key;
-const Point = @import("point.zig").Point;
-const Size = @import("point.zig").Point;
-const Cell = @import("cell.zig");
-
-const log = std.log.scoped(.terminal);
-
 // Ref: https://vt100.net/docs/vt510-rm/DECRPM.html
 pub const ReportMode = enum {
     not_recognized,
@@ -21,89 +9,95 @@ pub const ReportMode = enum {
 
 /// Gets number of rows and columns in the terminal
 pub fn getTerminalSize() Size {
-    var ws: std.posix.winsize = undefined;
-    _ = std.posix.system.ioctl(std.posix.STDIN_FILENO, std.posix.T.IOCGWINSZ, @intFromPtr(&ws));
+    var ws: posix.winsize = undefined;
+    _ = posix.system.ioctl(posix.STDIN_FILENO, posix.T.IOCGWINSZ, @intFromPtr(&ws));
     return .{ .x = ws.col, .y = ws.row };
 }
 
 pub fn saveScreen() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.save_screen);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.save_screen);
 }
 
 pub fn restoreScreen() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.restore_screen);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.restore_screen);
 }
 
 pub fn enterAltScreen() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.smcup);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.smcup);
 }
 
 pub fn exitAltScreen() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.rmcup);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.rmcup);
 }
 
 pub fn clearScreen() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.clear_screen);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.clear_screen);
 }
 
 pub fn hideCursor() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.hide_cursor);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.hide_cursor);
 }
 
 pub fn showCursor() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.show_cursor);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.show_cursor);
 }
 
 pub fn setCursorPositionHome() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.home);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.home);
 }
 
 pub fn enableMouseSupport() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.mouse_set);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.mouse_set);
 }
 
 pub fn disableMouseSupport() !void {
-    _ = try std.posix.write(std.posix.STDIN_FILENO, ctlseqs.mouse_reset);
+    _ = try posix.write(posix.STDIN_FILENO, ctlseqs.mouse_reset);
 }
 
 pub fn read(buf: []u8) !usize {
-    return try std.posix.read(std.posix.STDIN_FILENO, buf);
+    return try posix.read(posix.STDIN_FILENO, buf);
 }
 
 pub fn write(buf: []const u8) !usize {
-    return try std.posix.write(std.posix.STDIN_FILENO, buf);
+    return try posix.write(posix.STDIN_FILENO, buf);
 }
 
-fn contextWrite(context: @This(), data: []const u8) anyerror!usize {
-    _ = context;
-    return try std.posix.write(std.posix.STDOUT_FILENO, data);
+fn drainFn(w: *std.Io.Writer, data: []const []const u8, splat: usize) error{WriteFailed}!usize {
+    _ = w;
+    if (data.len == 0 or splat == 0) return 0;
+    var len: usize = 0;
+
+    for (data) |bytes| len += posix.write(posix.STDOUT_FILENO, bytes) catch return error.WriteFailed;
+
+    return len;
 }
 
-const Writer = std.io.Writer(
-    @This(),
-    anyerror,
-    contextWrite,
-);
-
-pub fn writer() Writer {
-    return .{ .context = .{} };
+// TODO I now need to add that much, for just the one function above?
+pub fn writer() std.Io.Writer {
+    return .{
+        .vtable = &.{
+            .drain = drainFn,
+            .flush = std.Io.Writer.noopFlush,
+        },
+        .buffer = &.{},
+    };
 }
 
 pub fn setCursorPosition(pos: Point) !void {
     var buf: [64]u8 = undefined;
-    const value = try std.fmt.bufPrint(&buf, "\x1b[{d};{d}H", .{ pos.y, pos.x });
-    _ = try std.posix.write(std.posix.STDIN_FILENO, value);
+    const value = try std.fmt.bufPrint(&buf, "\x1b[{d};{d}H", .{ pos.y + 1, pos.x + 1 });
+    _ = try posix.write(posix.STDIN_FILENO, value);
 }
 
 pub fn getCursorPosition() !Size.Position {
     // Needs Raw mode (no wait for \n) to work properly cause
     // control sequence will not be written without it.
-    _ = try std.posix.write(std.posix.STDIN_FILENO, "\x1b[6n");
+    _ = try posix.write(posix.STDIN_FILENO, "\x1b[6n");
 
     var buf: [64]u8 = undefined;
 
     // format: \x1b, "[", R1,..., Rn, ";", C1, ..., Cn, "R"
-    const len = try std.posix.read(std.posix.STDIN_FILENO, &buf);
+    const len = try posix.read(posix.STDIN_FILENO, &buf);
 
     if (!isCursorPosition(buf[0..len])) {
         return error.InvalidValueReturned;
@@ -166,8 +160,8 @@ pub fn isCursorPosition(buf: []u8) bool {
 ///
 /// `bak`: pointer to store termios struct backup before
 /// altering, this is used to disable raw mode.
-pub fn enableRawMode(bak: *std.posix.termios) !void {
-    var termios = try std.posix.tcgetattr(std.posix.STDIN_FILENO);
+pub fn enableRawMode(bak: *posix.termios) !void {
+    var termios = try posix.tcgetattr(posix.STDIN_FILENO);
     bak.* = termios;
 
     // termios flags used by termios(3)
@@ -192,20 +186,20 @@ pub fn enableRawMode(bak: *std.posix.termios) !void {
     termios.cflag.CSIZE = .CS8;
     termios.cflag.PARENB = false;
 
-    termios.cc[@intFromEnum(std.posix.V.MIN)] = 1;
-    termios.cc[@intFromEnum(std.posix.V.TIME)] = 0;
+    termios.cc[@intFromEnum(posix.V.MIN)] = 1;
+    termios.cc[@intFromEnum(posix.V.TIME)] = 0;
 
-    try std.posix.tcsetattr(
-        std.posix.STDIN_FILENO,
+    try posix.tcsetattr(
+        posix.STDIN_FILENO,
         .FLUSH,
         termios,
     );
 }
 
 /// Reverts `enableRawMode` to restore initial functionality.
-pub fn disableRawMode(bak: *std.posix.termios) !void {
-    try std.posix.tcsetattr(
-        std.posix.STDIN_FILENO,
+pub fn disableRawMode(bak: *const posix.termios) !void {
+    try posix.tcsetattr(
+        posix.STDIN_FILENO,
         .FLUSH,
         bak.*,
     );
@@ -215,13 +209,13 @@ pub fn disableRawMode(bak: *std.posix.termios) !void {
 pub fn canSynchornizeOutput() !bool {
     // Needs Raw mode (no wait for \n) to work properly cause
     // control sequence will not be written without it.
-    _ = try std.posix.write(std.posix.STDIN_FILENO, "\x1b[?2026$p");
+    _ = try posix.write(posix.STDIN_FILENO, "\x1b[?2026$p");
 
     var buf: [64]u8 = undefined;
 
     // format: \x1b, "[", "?", "2", "0", "2", "6", ";", n, "$", "y"
-    const len = try std.posix.read(std.posix.STDIN_FILENO, &buf);
-    if (!std.mem.eql(u8, buf[0..len], "\x1b[?2026;") or len < 9) {
+    const len = try posix.read(posix.STDIN_FILENO, &buf);
+    if (!mem.eql(u8, buf[0..len], "\x1b[?2026;") or len < 9) {
         return false;
     }
 
@@ -238,3 +232,16 @@ fn getReportMode(ps: u8) ReportMode {
         else => ReportMode.not_recognized,
     };
 }
+
+const log = std.log.scoped(.terminal);
+
+const std = @import("std");
+const mem = std.mem;
+const posix = std.posix;
+const assert = std.debug.assert;
+const ctlseqs = @import("ctlseqs.zig");
+const input = @import("input.zig");
+const Key = input.Key;
+const Point = @import("point.zig").Point;
+const Size = @import("point.zig").Point;
+const Cell = @import("cell.zig");

src/testing.zig

@@ -1,23 +1,12 @@
 //! Testing namespace for `zterm` to provide testing capabilities for `Containers`, `Event` handling, `App`s and `Element` implementations.
-const std = @import("std");
-const event = @import("event.zig");
-const Container = @import("container.zig").Container;
-
-const Cell = @import("cell.zig");
-const DisplayWidth = @import("DisplayWidth");
-const Point = @import("point.zig").Point;
-
-// TODO how would I describe the expected screens?
-// - including styling?
-// - compare generated strings instead? -> how would this be generated for the user?
 
 /// Single-buffer test rendering pipeline for testing purposes.
 pub const Renderer = struct {
-    allocator: std.mem.Allocator,
+    allocator: Allocator,
     size: Point,
     screen: []Cell,
 
-    pub fn init(allocator: std.mem.Allocator, size: Point) @This() {
+    pub fn init(allocator: Allocator, size: Point) @This() {
         const screen = allocator.alloc(Cell, @as(usize, size.x) * @as(usize, size.y)) catch @panic("testing.zig: Out of memory.");
         @memset(screen, .{});
 
@@ -45,10 +34,10 @@ pub const Renderer = struct {
         @memset(this.screen, .{});
     }
 
-    pub fn render(this: *@This(), comptime T: type, container: *const T) !void {
+    pub fn render(this: *@This(), comptime T: type, container: *const T, comptime Model: type, model: *const Model) !void {
         const size: Point = container.size;
         const origin: Point = container.origin;
-        const cells: []const Cell = try container.content();
+        const cells: []const Cell = try container.content(model);
 
         if (cells.len == 0) return;
 
@@ -69,7 +58,7 @@ pub const Renderer = struct {
         // free immediately
         container.allocator.free(cells);
 
-        for (container.elements.items) |*element| try this.render(T, element);
+        for (container.elements.items) |*element| try this.render(T, element, Model, model);
     }
 
     pub fn save(this: @This(), writer: anytype) !void {
@@ -85,6 +74,8 @@ pub const Renderer = struct {
 /// Create a .zon file containing the expected `Cell` slice using the `zterm.testing.Renderer.save` method:
 ///
 /// ```zig
+/// const Model = struct {};
+/// var model: Model = .{};
 /// const file = try std.fs.cwd().createFile("test/container/border/all.zon", .{ .truncate = true });
 /// defer file.close();
 ///
@@ -92,8 +83,8 @@ pub const Renderer = struct {
 /// var renderer: testing.Renderer = .init(allocator, size);
 /// defer renderer.deinit();
 ///
-/// try container.handle(.{ .size = size });
-/// try renderer.render(Container(event.SystemEvent), &container);
+/// try container.handle(&model, .{ .size = size });
+/// try renderer.render(@TypeOf(container), &container, Model, &.{});
 /// try renderer.save(file.writer());
 /// ```
 ///
@@ -102,7 +93,8 @@ pub const Renderer = struct {
 /// Then later load that .zon file at compile time and run your test against this `Cell` slice.
 ///
 /// ```zig
-/// var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+/// const Model = struct {};
+/// var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
 ///     .border = .{
 ///         .color = .green,
 ///         .sides = .all,
@@ -113,54 +105,81 @@ pub const Renderer = struct {
 /// try testing.expectContainerScreen(.{
 ///     .rows = 20,
 ///     .cols = 30,
-/// }, &container, @import("test/container/border.all.zon"));
+/// }, @TypeOf(container), &container, Model, @import("test/container/border.all.zon"));
 /// ```
-pub fn expectContainerScreen(size: Point, container: *Container(event.SystemEvent), expected: []const Cell) !void {
-    const allocator = std.testing.allocator;
+pub fn expectContainerScreen(size: Point, comptime T: type, container: *T, comptime Model: type, expected: []const Cell) !void {
+    const allocator = testing.allocator;
     var renderer: Renderer = .init(allocator, size);
     defer renderer.deinit();
 
-    try renderer.resize(size);
     container.resize(size);
     container.reposition(.{});
-    try renderer.render(Container(event.SystemEvent), container);
+    try renderer.render(T, container, Model, &.{});
 
     try expectEqualCells(.{}, renderer.size, expected, renderer.screen);
 }
 
+/// Taken from: https://codeberg.org/atman/zg/src/branch/master/src/DisplayWidth.zig
+/// Owned by https://codeberg.org/atman licensed under MIT all credits for this function go to him
+fn center(allocator: Allocator, str: []const u8, total_width: usize, pad: []const u8) ![]u8 {
+    if (str.len > total_width) return error.StrTooLong;
+    if (str.len == total_width) return try allocator.dupe(u8, str);
+
+    if (pad.len > total_width or str.len + pad.len > total_width) return error.PadTooLong;
+
+    const margin_width = @divFloor((total_width - str.len), 2);
+    if (pad.len > margin_width) return error.PadTooLong;
+
+    const extra_pad: usize = if (total_width % 2 != str.len % 2) 1 else 0;
+    const pads = @divFloor(margin_width, pad.len) * 2 + extra_pad;
+
+    var result = try allocator.alloc(u8, pads * pad.len + str.len);
+    var bytes_index: usize = 0;
+    var pads_index: usize = 0;
+
+    while (pads_index < pads / 2) : (pads_index += 1) {
+        @memcpy(result[bytes_index..][0..pad.len], pad);
+        bytes_index += pad.len;
+    }
+
+    @memcpy(result[bytes_index..][0..str.len], str);
+    bytes_index += str.len;
+
+    pads_index = 0;
+    while (pads_index < pads / 2 + extra_pad) : (pads_index += 1) {
+        @memcpy(result[bytes_index..][0..pad.len], pad);
+        bytes_index += pad.len;
+    }
+
+    return result;
+}
+
 /// This function is intended to be used only in tests. Test if the two
 /// provided cell arrays are identical. Usually the `Cell` slices are
 /// the contents of a given screen from the `zterm.testing.Renderer`. See
 /// `zterm.testing.expectContainerScreen` for an example usage.
 pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actual: []const Cell) !void {
-    const allocator = std.testing.allocator;
+    const allocator = testing.allocator;
 
-    try std.testing.expectEqual(expected.len, actual.len);
-    try std.testing.expectEqual(expected.len, @as(usize, size.y) * @as(usize, size.x));
+    try testing.expectEqual(expected.len, actual.len);
+    try testing.expectEqual(expected.len, @as(usize, size.y) * @as(usize, size.x));
 
     var expected_cps = try std.ArrayList(Cell).initCapacity(allocator, size.x);
-    defer expected_cps.deinit();
+    defer expected_cps.deinit(allocator);
 
     var actual_cps = try std.ArrayList(Cell).initCapacity(allocator, size.x);
-    defer actual_cps.deinit();
+    defer actual_cps.deinit(allocator);
 
-    var output = try std.ArrayList(u8).initCapacity(allocator, expected_cps.capacity * actual_cps.capacity + 5 * size.y);
-    defer output.deinit();
+    var allocating_writer = std.Io.Writer.Allocating.init(allocator);
+    defer allocating_writer.deinit();
 
-    var buffer = std.io.bufferedWriter(output.writer());
-    defer buffer.flush() catch {};
-
-    const writer = buffer.writer();
+    var writer = &allocating_writer.writer;
     var differ = false;
 
-    const dwd = try DisplayWidth.DisplayWidthData.init(allocator);
-    defer dwd.deinit();
-    const dw: DisplayWidth = .{ .data = &dwd };
-
-    const expected_centered = try dw.center(allocator, "Expected Screen", size.x, " ");
+    const expected_centered = try center(allocator, "Expected Screen", size.x, " ");
     defer allocator.free(expected_centered);
 
-    const actual_centered = try dw.center(allocator, "Actual Screen", size.x, " ");
+    const actual_centered = try center(allocator, "Actual Screen", size.x, " ");
     defer allocator.free(actual_centered);
 
     try writer.print("Screens are not equivalent.\n{s} ┆ {s}\n", .{ expected_centered, actual_centered });
@@ -176,8 +195,8 @@ pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actu
 
             if (!expected_cell.eql(actual_cell)) differ = true;
 
-            try expected_cps.append(expected_cell);
-            try actual_cps.append(actual_cell);
+            try expected_cps.append(allocator, expected_cell);
+            try actual_cps.append(allocator, actual_cell);
         }
 
         // write screens both formatted to buffer
@@ -190,12 +209,22 @@ pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actu
     if (!differ) return;
 
     // test failed
-    try buffer.flush();
+    debug.lockStdErr();
+    defer debug.unlockStdErr();
 
-    std.debug.lockStdErr();
-    defer std.debug.unlockStdErr();
-
-    const std_writer = std.io.getStdErr().writer();
-    try std_writer.writeAll(output.items);
+    var stdout_buffer: [1024]u8 = undefined;
+    var stdout = std.fs.File.stdout().writer(&stdout_buffer);
+    const stdout_writer = &stdout.interface;
+    try stdout_writer.writeAll(writer.buffer[0..writer.end]);
+    try stdout_writer.flush();
     return error.TestExpectEqualCells;
 }
+
+const std = @import("std");
+const debug = std.debug;
+const testing = std.testing;
+const Allocator = std.mem.Allocator;
+const event = @import("event.zig");
+const Container = @import("container.zig").Container;
+const Cell = @import("cell.zig");
+const Point = @import("point.zig").Point;