Properly repaint RenderLayer's descendants when it moves

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 239 matching lines @@
 void RenderLayer::updateLayerPositionsAfterLayout(const RenderLayer* rootLayer, UpdateLayerPositionsFlags flags)
 {
     TRACE_EVENT0("blink_rendering", "RenderLayer::updateLayerPositionsAfterLayout");
 
     // FIXME: Remove incremental compositing updates after fixing the chicken/egg issues
     // https://code.google.com/p/chromium/issues/detail?id=343756
     DisableCompositingQueryAsserts disabler;
     updateLayerPositionRecursive(flags);
 }
 
+void RenderLayer::markDescendantLayersMayNeedPaintInvalidation()
+{
+    for (RenderLayer* childLayer = firstChild(); childLayer; childLayer = childLayer->nextSibling()) {

[esprehn, 2014/06/24 20:37:07]

We should take a different approach than this and mark a "Forced" update type on
this layer, and then during the walk the Force should make us traverse down the
subtree. What you've added here is going to walk down the subtree over and over
again.

+        childLayer->renderer()->setMayNeedPaintInvalidation(true);
+        childLayer->markDescendantLayersMayNeedPaintInvalidation();
+    }
+}
+
 void RenderLayer::updateLayerPositionRecursive(UpdateLayerPositionsFlags flags)
 {
-    updateLayerPosition();
+    if (updateLayerPosition())
+        markDescendantLayersMayNeedPaintInvalidation();

[esprehn, 2014/06/24 20:37:07]

Doesn't this make us traverse down the same subtree repeatedly?

 
     // Clear our cached clip rect information.
     m_clipper.clearClipRects();
 
     if (hasOverflowControls()) {
         // FIXME: We should figure out the right time to position the overflow controls.
         // This call appears to be necessary to pass some layout test that use EventSender,
         // presumably because the normal time to position the controls is during paint. We
         // probably shouldn't position the overflow controls during paint either...
         scrollableArea()->positionOverflowControls(IntSize());
@@ skipping 3508 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif