Clear absolute clip rects when transform changes

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 470 matching lines @@
     }
 
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->updateLayerPositionsAfterScroll(flags);
 
     // We don't update our reflection as scrolling is a translation which does not change the size()
     // of an object, thus RenderReplica will still repaint itself properly as the layer position was
     // updated above.
 }
 
-void RenderLayer::updateTransform()
+void RenderLayer::updateTransformationMatrix()
 {
+    if (m_transform) {
+        RenderBox* box = renderBox();
+        ASSERT(box);
+        m_transform->makeIdentity();
+        box->style()->applyTransform(*m_transform, box->pixelSnappedBorderBoxRect().size(), RenderStyle::IncludeTransformOrigin);
+        makeMatrixRenderable(*m_transform, compositor()->hasAcceleratedCompositing());
+    }
+}
+
+void RenderLayer::updateTransform(const RenderStyle* oldStyle, RenderStyle* newStyle)
+{
+    if (oldStyle && newStyle->transformDataEquivalent(*oldStyle))
+        return;
+
     // hasTransform() on the renderer is also true when there is transform-style: preserve-3d or perspective set,
     // so check style too.
-    bool hasTransform = renderer()->hasTransform() && renderer()->style()->hasTransform();
+    bool hasTransform = renderer()->hasTransform() && newStyle->hasTransform();
     bool had3DTransform = has3DTransform();
 
     bool hadTransform = m_transform;
     if (hasTransform != hadTransform) {
         if (hasTransform)
             m_transform = adoptPtr(new TransformationMatrix);
         else
             m_transform.clear();
 
         // Layers with transforms act as clip rects roots, so clear the cached clip rects here.
         m_clipper.clearClipRectsIncludingDescendants();
+    } else if (hasTransform) {
+        m_clipper.clearClipRectsIncludingDescendants(AbsoluteClipRects);
     }
 
-    if (hasTransform) {
-        RenderBox* box = renderBox();
-        ASSERT(box);
-        m_transform->makeIdentity();
-        box->style()->applyTransform(*m_transform, box->pixelSnappedBorderBoxRect().size(), RenderStyle::IncludeTransformOrigin);
-        makeMatrixRenderable(*m_transform, compositor()->hasAcceleratedCompositing());
-    }
+    updateTransformationMatrix();
 
     if (had3DTransform != has3DTransform())

[ajuma, 2014/06/17 23:21:39]

We don't need to also check this in the post-layout update (when
updateTransformationMatrix is called by
RenderBox::updateLayerTransformAfterLayout), since the z-coordinate of
transform-origin is always expressed as a length rather than as a percent of box
size, so won't be changed by layout.

         dirty3DTransformedDescendantStatus();
 }
 
 static RenderLayer* enclosingLayerForContainingBlock(RenderLayer* layer)
 {
     if (RenderObject* containingBlock = layer->renderer()->containingBlock())
         return containingBlock->enclosingLayer();
     return 0;
 }
 
@@ skipping 3157 matching lines @@
     if (!oldStyle || !renderer()->style()->reflectionDataEquivalent(oldStyle)) {
         ASSERT(!oldStyle || diff.needsFullLayout());
         updateReflectionInfo(oldStyle);
     }
 
     if (RuntimeEnabledFeatures::cssCompositingEnabled())
         m_blendInfo.updateBlendMode();
 
     updateDescendantDependentFlags();
 
-    if (!oldStyle || !renderer()->style()->transformDataEquivalent(*oldStyle))
-        updateTransform();
+    updateTransform(oldStyle, renderer()->style());
 
     {
         // https://code.google.com/p/chromium/issues/detail?id=343759
         DisableCompositingQueryAsserts disabler;
         updateFilters(oldStyle, renderer()->style());
     }
 
     compositor()->updateStyleDeterminedCompositingReasons(this);
 
     setNeedsCompositingInputsUpdate();
@@ skipping 157 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif