Bug fix: moving windows slightly when dragging slider

egui/src/containers/window.rs

@@ -466,8 +466,17 @@ fn move_and_resize_window(ctx: &Context, window_interaction: &WindowInteraction)
             rect.max.y = ctx.round_to_pixel(pointer_pos.y);
         }
     } else {
-        // movement
+        // Movement.
-        rect = rect.translate(pointer_pos - ctx.input().pointer.press_origin()?);
+
+        // We do window interaction first (to avoid frame delay),
+        // but we want anything interactive in the window (e.g. slider) to steal
+        // the drag from us. It is therefor important not to move the window the first frame,
+        // but instead let other widgets to the steal. HACK.
+        if !ctx.input().pointer.any_pressed() {
+            let press_origin = ctx.input().pointer.press_origin()?;
+            let delta = pointer_pos - press_origin;
+            rect = rect.translate(delta);
+        }
     }
 
     Some(rect)

egui/src/context.rs

@@ -293,6 +293,11 @@ impl CtxRef {
                             response.is_pointer_button_down_on = true;
                         }
 
+                        // HACK: windows have low priority on dragging.
+                        // This is so that if you drag a slider in a window,
+                        // the slider will steal the drag away from the window.
+                        // This is needed because we do window interaction first (to prevent frame delay),
+                        // and then do content layout.
                         if sense.drag
                             && (memory.interaction.drag_id.is_none()
                                 || memory.interaction.drag_is_window)