Add Ui::with_transform, making it possible to transform widgets witho…

…ut creating a new layer

crates/egui/src/layers.rs

@@ -124,10 +124,14 @@ impl PaintList {
         self.0.is_empty()
     }
 
+    pub fn next_idx(&self) -> ShapeIdx {
+        ShapeIdx(self.0.len())
+    }
+
     /// Returns the index of the new [`Shape`] that can be used with `PaintList::set`.
     #[inline(always)]
     pub fn add(&mut self, clip_rect: Rect, shape: Shape) -> ShapeIdx {
-        let idx = ShapeIdx(self.0.len());
+        let idx = self.next_idx();
         self.0.push(ClippedShape { clip_rect, shape });
         idx
     }
@@ -171,6 +175,14 @@ impl PaintList {
         }
     }
 
+    /// Transform each [`Shape`] and clip rectangle in range by this much, in-place
+    pub fn transform_range(&mut self, start: ShapeIdx, end: ShapeIdx, transform: TSTransform) {
+        for ClippedShape { clip_rect, shape } in &mut self.0[start.0..end.0] {
+            *clip_rect = transform.mul_rect(*clip_rect);
+            shape.transform(transform);
+        }
+    }
+
     /// Read-only access to all held shapes.
     pub fn all_entries(&self) -> impl ExactSizeIterator<Item = &ClippedShape> {
         self.0.iter()

crates/egui/src/ui.rs

@@ -2685,6 +2685,34 @@ impl Ui {
 
         (InnerResponse { inner, response }, payload)
     }
+
+    /// Create a new Scope and transform its contents via a [`TSTransform`].
+    /// This only affects visuals, inputs will not be transformed. So this is mostly useful
+    /// to create visual effects on interactions, e.g. scaling a button on hover / click.
+    ///
+    /// Check out [`Context::set_transform_layer`] for a persistent transform that also affects
+    /// inputs.
+    pub fn with_transform<R>(
+        &mut self,
+        transform: emath::TSTransform,
+        add_contents: impl FnOnce(&mut Self) -> R,
+    ) -> InnerResponse<R> {
+        let start_idx = self.ctx().graphics(|gx| {
+            gx.get(self.layer_id())
+                .map(|l| l.next_idx())
+                .unwrap_or(crate::layers::ShapeIdx(0))
+        });
+
+        let r = self.scope_dyn(UiBuilder::new(), Box::new(add_contents));
+
+        self.ctx().graphics_mut(|g| {
+            let list = g.entry(self.layer_id());
+            let end_idx = list.next_idx();
+            list.transform_range(start_idx, end_idx, transform)
+        });
+
+        r
+    }
 }
 
 /// # Menus