WIP - mask a view's layer by its view coordinates

ui/views/view.cc

Index: ui/views/view.cc
diff --git a/ui/views/view.cc b/ui/views/view.cc
index b6cd9d0e97f9345128f754a62f0b80e15fa2430f..3ef145ae65955ed8919eabcfc377555e43eb785c 100644
--- a/ui/views/view.cc
+++ b/ui/views/view.cc
@@ -821,6 +821,9 @@ void View::Paint(const ui::PaintContext& parent_context) {
       clip_path_in_parent.offset(GetMirroredX(), y());
       clip_recorder.ClipPathWithAntiAliasing(clip_path_in_parent);
     }
+  } else {
+    DCHECK(layer());
+    clip_recorder.ClipRect(GetVisibleBounds());

[sky, 2016/11/29 18:08:13]

Is this really enough? What happens if an animation occurs that effectively
moves the layer. Wouldn't the clip move with the layer, which isn't really waht
you want.

[Evan Stade, 2016/11/29 18:38:01]

when the layer is moved that affects the view's transform (as per GetTransform),
which is taken into account in GetVisibleBounds.

[sky, 2016/11/29 20:27:09]

That's assuming you end up here, right? If the layer is moved that is not
necessarily the case.

   }
 
   ui::TransformRecorder transform_recorder(context);
@@ -1379,10 +1382,12 @@ void View::PreferredSizeChanged() {
 }
 
 bool View::GetNeedsNotificationWhenVisibleBoundsChange() const {
-  return false;
+  return true;
 }
 
 void View::OnVisibleBoundsChanged() {
+  if (layer())
+    SchedulePaint();
 }
 
 // Tree operations -------------------------------------------------------------