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 b806e2cf2df5a3e0ef3cacef92aae2d3646e6ae2..bc83648c4ce63ea7b3bda57571e8f54cd04546ad 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -4099,7 +4099,7 @@ 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;
 
@@ -4123,7 +4123,7 @@ void RenderBox::incrementallyInvalidatePaint(const RenderLayerModelObject& paint
             positionFromPaintInvalidationContainer.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.
@@ -4137,10 +4137,26 @@ void RenderBox::incrementallyInvalidatePaint(const RenderLayerModelObject& paint
             positionFromPaintInvalidationContainer.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 they equal;
+    // - Invalidate the bigger one if one contains another;
+    // - Otherwise invalidate both.
+    bool equal = rectClippedByOldBounds == rectClippedByNewBounds;

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

(FYI as it's on the old patch) coding style violation: booleans should include a
verb (usually be or do).

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

Acknowledged.

+    if (equal || !rectClippedByNewBounds.contains(rectClippedByOldBounds))
+        invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByOldBounds, InvalidationIncremental);
+    if (!equal && !rectClippedByOldBounds.contains(rectClippedByNewBounds))
+        invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByNewBounds, InvalidationIncremental);

[dsinclair, 2014/09/16 15:24:01]

This maybe a bit easier to read if the conditions are broken apart.

if (rectClippedByOldBounds == rectClippedByNewBounds) {
  invalidatePaintUsingContainer(..., rectClipedByOldBounds, ...);
  return;
}

if (!rectClippedByNewBounds.contains(rectClippedByOldBounds))
  invalidatePaintUsingContainer(..., rectClippedByOldBounds, ...)

if (!rectClippedByOldBounds.contains(rectClippedByNewBounds))
  invalidatePaintUsingContainer(..., rectClippedByNewBounds))

[Xianzhu, 2014/09/16 15:53:27]

Good idea. Done.

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