From 4cde0640c8d804e438d174b6a49159dac09a3475 Mon Sep 17 00:00:00 2001
From: Yves Biener <yves.biener@gmx.de>
Date: Thu, 22 May 2025 23:39:05 +0200
Subject: [PATCH] fix(element/scrollable): adjust anchor for scrollable element
 during resize

---
 src/element.zig | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/element.zig b/src/element.zig
index 8e74454..3beb1ff 100644
--- a/src/element.zig
+++ b/src/element.zig
@@ -109,20 +109,28 @@ pub fn Scrollable(Event: type) type {
 
         fn resize(ctx: *anyopaque, size: Point) void {
             const this: *@This() = @ptrCast(@alignCast(ctx));
-            this.size = size;
+            const last_max_anchor_x = this.container_size.x -| this.size.x;
+            const last_max_anchor_y = this.container_size.y -| this.size.y;
 
+            this.size = size;
             this.container.resize(size);
             if (this.configuration.scrollbar) {
                 if (this.container.properties.size.dim.x > this.size.x or this.container.size.x > this.size.x) this.configuration.y_axis = true;
                 if (this.container.properties.size.dim.y > this.size.y or this.container.size.y > this.size.y) this.configuration.x_axis = true;
 
-                if (this.configuration.x_axis or this.configuration.y_axis)
-                    this.container.resize(.{
-                        .x = this.size.x - if (this.configuration.x_axis) @as(u16, 1) else @as(u16, 0),
-                        .y = this.size.y - if (this.configuration.y_axis) @as(u16, 1) else @as(u16, 0),
-                    });
+                if (this.configuration.x_axis or this.configuration.y_axis) this.container.resize(.{
+                    .x = this.size.x - if (this.configuration.x_axis) @as(u16, 1) else @as(u16, 0),
+                    .y = this.size.y - if (this.configuration.y_axis) @as(u16, 1) else @as(u16, 0),
+                });
             }
 
+            const new_max_anchor_x = this.container.size.x -| size.x;
+            const new_max_anchor_y = this.container.size.y -| size.y;
+
+            // correct anchor if necessary
+            if (new_max_anchor_x < last_max_anchor_x and this.anchor.x > new_max_anchor_x) this.anchor.x = new_max_anchor_x;
+            if (new_max_anchor_y < last_max_anchor_y and this.anchor.y > new_max_anchor_y) this.anchor.y = new_max_anchor_y;
+
             this.container_size = this.container.size;
         }
 
@@ -140,8 +148,8 @@ pub fn Scrollable(Event: type) type {
                         this.anchor.y -|= 1;
                     },
                     Mouse.Button.wheel_down => if (this.container_size.y > this.size.y) {
-                        const max_origin_y = this.container_size.y -| this.size.y;
-                        this.anchor.y = @min(this.anchor.y + 1, max_origin_y);
+                        const max_anchor_y = this.container_size.y -| this.size.y;
+                        this.anchor.y = @min(this.anchor.y + 1, max_anchor_y);
                     },
                     Mouse.Button.wheel_left => if (this.container_size.x > this.size.x) {
                         this.anchor.x -|= 1;