Bug 641770. Ensure that the cliprect for a layer is interpreted in the coordinate system of its container in MarkLeafLayersCoveredByOpaque. r=bas

gfx/layers/basic/BasicLayers.cpp

@@ -1259,6 +1259,7 @@ TransformIntRect(nsIntRect& aRect, const gfxMatrix& aMatrix,
 // This implementation assumes that GetEffectiveTransform transforms
 // all layers to the same coordinate system. It can't be used as is
 // by accelerated layers because of intermediate surfaces.
+// aClipRect and aRegion are in that global coordinate system.
 static void
 MarkLeafLayersCoveredByOpaque(Layer* aLayer, const nsIntRect& aClipRect,
                               nsIntRegion& aRegion)
@@ -1267,7 +1268,6 @@ MarkLeafLayersCoveredByOpaque(Layer* aLayer, const nsIntRect& aClipRect,
   BasicImplData* data = ToData(aLayer);
   data->SetCoveredByOpaque(PR_FALSE);
 
-  const nsIntRect* clipRect = aLayer->GetEffectiveClipRect();
   nsIntRect newClipRect(aClipRect);
 
   // Allow aLayer or aLayer's descendants to cover underlying layers
@@ -1277,14 +1277,21 @@ MarkLeafLayersCoveredByOpaque(Layer* aLayer, const nsIntRect& aClipRect,
     newClipRect.SetRect(0, 0, 0, 0);
   }
 
+  {
+    const nsIntRect* clipRect = aLayer->GetEffectiveClipRect();
     if (clipRect) {
       nsIntRect cr = *clipRect;
+      // clipRect is in the container's coordinate system. Get it into the
+      // global coordinate system.
+      if (aLayer->GetParent()) {
         gfxMatrix tr;
-    if (aLayer->GetEffectiveTransform().Is2D(&tr)) {
+        if (aLayer->GetParent()->GetEffectiveTransform().Is2D(&tr)) {
           TransformIntRect(cr, tr, ToInsideIntRect);
-      newClipRect.IntersectRect(newClipRect, cr);
         } else {
-      newClipRect.SetRect(0, 0, 0, 0);
+          cr.SetRect(0, 0, 0, 0);
+        }
+      }
+      newClipRect.IntersectRect(newClipRect, cr);
     }
   }