Change the resize cursor when you reach the resize limit (#4275)

For panels and `DragValue`: if you cannot resize more in one direction,
reflect that in the choice of mouse cursor


![resize-cursor-2](https://github.com/emilk/egui/assets/1148717/f95176d3-eab9-48cf-b7bd-3182312551d9)

crates/egui/src/containers/panel.rs

@@ -228,8 +228,8 @@ impl SidePanel {
 
         let available_rect = ui.available_rect_before_wrap();
         let mut panel_rect = available_rect;
+        let mut width = default_width;
         {
-            let mut width = default_width;
             if let Some(state) = PanelState::load(ui.ctx(), id) {
                 width = state.rect.width();
             }
@@ -249,9 +249,8 @@ impl SidePanel {
 
                 if is_resizing {
                     if let Some(pointer) = resize_response.interact_pointer_pos() {
-                        let width = (pointer.x - side.side_x(panel_rect)).abs();
-                        let width =
-                            clamp_to_range(width, width_range).at_most(available_rect.width());
+                        width = (pointer.x - side.side_x(panel_rect)).abs();
+                        width = clamp_to_range(width, width_range).at_most(available_rect.width());
                         side.set_rect_width(&mut panel_rect, width);
                     }
                 }
@@ -296,7 +295,14 @@ impl SidePanel {
         }
 
         if resize_hover || is_resizing {
-            ui.ctx().set_cursor_icon(CursorIcon::ResizeHorizontal);
+            let cursor_icon = if width <= width_range.min {
+                CursorIcon::ResizeEast
+            } else if width < width_range.max {
+                CursorIcon::ResizeHorizontal
+            } else {
+                CursorIcon::ResizeWest
+            };
+            ui.ctx().set_cursor_icon(cursor_icon);
         }
 
         PanelState { rect }.store(ui.ctx(), id);
@@ -684,12 +690,13 @@ impl TopBottomPanel {
 
         let available_rect = ui.available_rect_before_wrap();
         let mut panel_rect = available_rect;
+
+        let mut height = if let Some(state) = PanelState::load(ui.ctx(), id) {
+            state.rect.height()
+        } else {
+            default_height.unwrap_or_else(|| ui.style().spacing.interact_size.y)
+        };
         {
-            let mut height = if let Some(state) = PanelState::load(ui.ctx(), id) {
-                state.rect.height()
-            } else {
-                default_height.unwrap_or_else(|| ui.style().spacing.interact_size.y)
-            };
             height = clamp_to_range(height, height_range).at_most(available_rect.height());
             side.set_rect_height(&mut panel_rect, height);
             ui.ctx()
@@ -707,8 +714,8 @@ impl TopBottomPanel {
 
                 if is_resizing {
                     if let Some(pointer) = resize_response.interact_pointer_pos() {
-                        let height = (pointer.y - side.side_y(panel_rect)).abs();
-                        let height =
+                        height = (pointer.y - side.side_y(panel_rect)).abs();
+                        height =
                             clamp_to_range(height, height_range).at_most(available_rect.height());
                         side.set_rect_height(&mut panel_rect, height);
                     }
@@ -755,7 +762,14 @@ impl TopBottomPanel {
         }
 
         if resize_hover || is_resizing {
-            ui.ctx().set_cursor_icon(CursorIcon::ResizeVertical);
+            let cursor_icon = if height <= height_range.min {
+                CursorIcon::ResizeSouth
+            } else if height < height_range.max {
+                CursorIcon::ResizeVertical
+            } else {
+                CursorIcon::ResizeNorth
+            };
+            ui.ctx().set_cursor_icon(cursor_icon);
         }
 
         PanelState { rect }.store(ui.ctx(), id);

crates/egui/src/containers/window.rs

@@ -697,6 +697,7 @@ impl ResizeInteraction {
         let top = self.top.any();
         let bottom = self.bottom.any();
 
+        // TODO(emilk): use one-sided cursors for when we reached the min/max size.
         if (left && top) || (right && bottom) {
             ctx.set_cursor_icon(CursorIcon::ResizeNwSe);
         } else if (right && top) || (left && bottom) {

crates/egui/src/widgets/drag_value.rs

@@ -525,8 +525,16 @@ impl<'a> Widget for DragValue<'a> {
             .sense(Sense::click_and_drag())
             .min_size(ui.spacing().interact_size); // TODO(emilk): find some more generic solution to `min_size`
 
+            let cursor_icon = if value <= *clamp_range.start() {
+                CursorIcon::ResizeEast
+            } else if value < *clamp_range.end() {
+                CursorIcon::ResizeHorizontal
+            } else {
+                CursorIcon::ResizeWest
+            };
+
             let response = ui.add(button);
-            let mut response = response.on_hover_cursor(CursorIcon::ResizeHorizontal);
+            let mut response = response.on_hover_cursor(cursor_icon);
 
             if ui.style().explanation_tooltips {
                 response = response.on_hover_text(format!(
@@ -552,7 +560,7 @@ impl<'a> Widget for DragValue<'a> {
                 )));
                 state.store(ui.ctx(), response.id);
             } else if response.dragged() {
-                ui.ctx().set_cursor_icon(CursorIcon::ResizeHorizontal);
+                ui.ctx().set_cursor_icon(cursor_icon);
 
                 let mdelta = response.drag_delta();
                 let delta_points = mdelta.x - mdelta.y; // Increase to the right and up