Fix drag-and-drop preview following emilk#3906

crates/egui/src/context.rs

@@ -2278,9 +2278,13 @@ impl Context {
 impl Context {
     /// Transform the graphics of the given layer.
     ///
+    /// This will also affect input.
+    ///
     /// This is a sticky setting, remembered from one frame to the next.
     ///
     /// Can be used to implement pan and zoom (see relevant demo).
+    ///
+    /// For a temporary transform, use [`Self::transform_layer_shapes`] instead.
     pub fn set_transform_layer(&self, layer_id: LayerId, transform: TSTransform) {
         self.memory_mut(|m| {
             if transform == TSTransform::IDENTITY {
@@ -2291,6 +2295,34 @@ impl Context {
         });
     }
 
+    /// Move all the graphics at the given layer.
+    ///
+    /// Is used to implement drag-and-drop preview.
+    ///
+    /// This only applied to the existing graphics at the layer, not to new graphics added later.
+    ///
+    /// For a persistent transform, use [`Self::set_transform_layer`] instead.
+    #[deprecated = "Use `transform_layer_shapes` instead"]
+    pub fn translate_layer(&self, layer_id: LayerId, delta: Vec2) {
+        if delta != Vec2::ZERO {
+            let transform = emath::TSTransform::from_translation(delta);
+            self.transform_layer_shapes(layer_id, transform);
+        }
+    }
+
+    /// Transform all the graphics at the given layer.
+    ///
+    /// Is used to implement drag-and-drop preview.
+    ///
+    /// This only applied to the existing graphics at the layer, not to new graphics added later.
+    ///
+    /// For a persistent transform, use [`Self::set_transform_layer`] instead.
+    pub fn transform_layer_shapes(&self, layer_id: LayerId, transform: TSTransform) {
+        if transform != TSTransform::IDENTITY {
+            self.graphics_mut(|g| g.entry(layer_id).transform(transform));
+        }
+    }
+
     /// Top-most layer at the given position.
     pub fn layer_id_at(&self, pos: Pos2) -> Option<LayerId> {
         self.memory(|mem| {

crates/egui/src/layers.rs

@@ -227,8 +227,17 @@ impl GraphicLayers {
             }
 
             // Also draw areas that are missing in `area_order`:
-            for shapes in order_map.values_mut() {
-                all_shapes.append(&mut shapes.0);
+            for (id, list) in order_map {
+                let layer_id = LayerId::new(order, *id);
+
+                if let Some(transform) = transforms.get(&layer_id) {
+                    for clipped_shape in &mut list.0 {
+                        clipped_shape.clip_rect = *transform * clipped_shape.clip_rect;
+                        clipped_shape.shape.transform(*transform);
+                    }
+                }
+
+                all_shapes.append(&mut list.0);
             }
         }
 

crates/egui/src/ui.rs

@@ -2177,7 +2177,7 @@ impl Ui {
             if let Some(pointer_pos) = self.ctx().pointer_interact_pos() {
                 let delta = pointer_pos - response.rect.center();
                 self.ctx()
-                    .set_transform_layer(layer_id, emath::TSTransform::from_translation(delta));
+                    .transform_layer_shapes(layer_id, emath::TSTransform::from_translation(delta));
             }
 
             InnerResponse::new(inner, response)