Invalidate the bigger rect if one rect contains the other in LayoutObject::fullyInvalidateRect()

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 0c6f807ad672cb735dc2bb633c22be393993eedb..fe5d7bcd8d996a955627057b95c6b58c5df8c755 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -1581,11 +1581,16 @@ void LayoutObject::incrementallyInvalidatePaint(const LayoutBoxModelObject& pain
 
 void LayoutObject::fullyInvalidatePaint(const LayoutBoxModelObject& paintInvalidationContainer, PaintInvalidationReason invalidationReason, const LayoutRect& oldBounds, const LayoutRect& newBounds)

[pdr., 2016/04/12 03:01:22]

This logic took me a while to reason through. It's correct, but I wonder if we
could make it easier to understand without affecting the compiled result? Maybe
something like the following where we don't re-use invalidationRect:

// The following logic avoids invalidating twice if one set of bounds contains
the other.
if (!oldBounds.contains(newBounds)) {
    LayoutRect invalidation = newBounds;
    adjustInvalidationRectForCompositedScrolling(invalidation,
paintInvalidationContainer);
    invalidatePaintUsingContainer(paintInvalidationContainer, invalidation,
invalidationReason);

    // Early out when the old bounds have already been invalidated.
    if (newBounds.contains(oldBounds))
       return;
}
LayoutRect invalidation = oldBounds;
adjustInvalidationRectForCompositedScrolling(invalidation,
paintInvalidationContainer);
invalidatePaintUsingContainer(paintInvalidationContainer, invalidation,
invalidationReason);

[Xianzhu, 2016/04/12 16:47:50]

Done (except that oldBounds and newBounds inversed to keep the sequence the same
as before if both need invalidation).

 {
-    // Otherwise do full paint invalidation.
     LayoutRect invalidationRect = oldBounds;
+    bool oneRectContainsTheOther = true;
+    if (newBounds.contains(oldBounds))
+        invalidationRect = newBounds;
+    else if (!oldBounds.contains(newBounds))
+        oneRectContainsTheOther = false;
+
     adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
     invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, invalidationReason);
-    if (newBounds != oldBounds) {
+    if (!oneRectContainsTheOther) {
         invalidationRect = newBounds;
         adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
         invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, invalidationReason);