Clear absolute clip rects when transform changes

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 041337f6fd6b25e64b4d608d8c43317525dc7f92..2df7c1a26c6b02f59484cdc540b2117a9f001400 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -488,11 +488,25 @@ void RenderLayer::updateLayerPositionsAfterScroll(UpdateLayerPositionsAfterScrol
     // 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;
@@ -504,15 +518,11 @@ void RenderLayer::updateTransform()
 
         // 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();
@@ -3692,8 +3702,7 @@ void RenderLayer::styleChanged(StyleDifference diff, const RenderStyle* oldStyle
 
     updateDescendantDependentFlags();
 
-    if (!oldStyle || !renderer()->style()->transformDataEquivalent(*oldStyle))
-        updateTransform();
+    updateTransform(oldStyle, renderer()->style());
 
     {
         // https://code.google.com/p/chromium/issues/detail?id=343759