Clip incremental invalidation rects for RenderBox

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index 3d40a296ec8b5e2f8ffab78926531778015280e8..193585a61245226eab182f47f007f1dea4ed0a4d 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -3892,7 +3892,7 @@ void RenderBox::incrementallyInvalidatePaint(const RenderLayerModelObject& paint
     LayoutSize oldBorderBoxSize = computePreviousBorderBoxSize(oldBounds.size());
     LayoutSize newBorderBoxSize = size();
 
-    // If border box size didn't change, RenderBox's incrementallyInvalidatePaint() is good.
+    // If border box size didn't change, RenderObject's incrementallyInvalidatePaint() is good.
     if (oldBorderBoxSize == newBorderBoxSize)
         return;
 
@@ -3916,7 +3916,7 @@ void RenderBox::incrementallyInvalidatePaint(const RenderLayerModelObject& paint
             positionFromPaintInvalidationBacking.y(),
             deltaWidth + borderWidth,
             std::max(oldBorderBoxSize.height(), newBorderBoxSize.height()));
-        invalidatePaintUsingContainer(&paintInvalidationContainer, rightDeltaRect, InvalidationIncremental);
+        invalidatePaintRectClippedByOldAndNewBounds(paintInvalidationContainer, rightDeltaRect, oldBounds, newBounds);
     }
 
     // Invalidate the bottom delta part and the bottom border of the old or new box which has smaller height.
@@ -3930,10 +3930,28 @@ void RenderBox::incrementallyInvalidatePaint(const RenderLayerModelObject& paint
             positionFromPaintInvalidationBacking.y() + smallerHeight - borderHeight,
             std::max(oldBorderBoxSize.width(), newBorderBoxSize.width()),
             deltaHeight + borderHeight);
-        invalidatePaintUsingContainer(&paintInvalidationContainer, bottomDeltaRect, InvalidationIncremental);
+        invalidatePaintRectClippedByOldAndNewBounds(paintInvalidationContainer, bottomDeltaRect, oldBounds, newBounds);
     }
 }
 
+void RenderBox::invalidatePaintRectClippedByOldAndNewBounds(const RenderLayerModelObject& paintInvalidationContainer, const LayoutRect& rect, const LayoutRect& oldBounds, const LayoutRect& newBounds)
+{
+    if (rect.isEmpty())
+        return;
+    LayoutRect rectClippedByOldBounds = intersection(rect, oldBounds);
+    LayoutRect rectClippedByNewBounds = intersection(rect, newBounds);
+    // Invalidate only once if the clipped rects equal.
+    if (rectClippedByOldBounds == rectClippedByNewBounds) {
+        invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByOldBounds, InvalidationIncremental);
+        return;
+    }
+    // Invalidate the bigger one if one contains another. Otherwise invalidate both.
+    if (!rectClippedByNewBounds.contains(rectClippedByOldBounds))
+        invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByOldBounds, InvalidationIncremental);
+    if (!rectClippedByOldBounds.contains(rectClippedByNewBounds))
+        invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByNewBounds, InvalidationIncremental);

[Julien - ping for review, 2014/09/16 18:22:52]

I count 3 cases for the non-equal case. Do we have really enough coverage for
all of them?

[Xianzhu, 2014/09/16 18:36:13]

Yes. The existing layout tests cover the cases. Actually the conditions were
added after I had noticed duplicated invalidation rects without the conditions
for existing layout tests. The new layout test just cover the clipping behavior.

+}
+
 void RenderBox::markForPaginationRelayoutIfNeeded(SubtreeLayoutScope& layoutScope)
 {
     ASSERT(!needsLayout());