Introducing LayoutObject::mapToVisibleRectInContainerSpace

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 3b671d8d42b3358bd8d550c09b3042365177e79c..0c834ad1d1175a5dd06b8b893f0eae9bd7ae7070 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -947,13 +947,6 @@ void LayoutBox::applyCachedClipAndScrollOffsetForPaintInvalidation(LayoutRect& p
     flipForWritingMode(paintRect);
     paintRect.move(-scrolledContentOffset()); // For overflow:auto/scroll/hidden.
 
-    // Do not clip scroll layer contents because the compositor expects the whole layer

[leviw_travelin_and_unemployed, 2015/12/09 23:06:26]

You said there's a use that prevents us from asserting don't cross a composited
scrolling boundary, no? Otherwise we should have that assert.

[szager1, 2015/12/09 23:21:26]

The use is IntersectionObserver :)

-    // to be always invalidated in-time.
-    if (usesCompositedScrolling()) {
-        flipForWritingMode(paintRect);
-        return;
-    }
-
     // size() is inaccurate if we're in the middle of a layout of this LayoutBox, so use the
     // layer's size instead. Even if the layer's size is wrong, the layer itself will issue paint invalidations
     // anyway if its size does change.
@@ -1932,7 +1925,7 @@ void LayoutBox::mapRectToPaintInvalidationBacking(const LayoutBoxModelObject* pa
     // FIXME: We ignore the lightweight clipping rect that controls use, since if |o| is in mid-layout,
     // its controlClipRect will be wrong. For overflow clip we use the values cached by the layer.
     rect.setLocation(topLeft);
-    if (o->hasOverflowClip()) {
+    if (o != paintInvalidationContainer && o->hasOverflowClip()) {

[leviw_travelin_and_unemployed, 2015/12/09 23:06:26]

May be worthy of a comment?

[szager1, 2015/12/09 23:21:26]

I'm not exactly sure what the comment should be.  I could copy the comment which
I deleted from applyCachedClipAndScrollOffsetForPaintInvalidation, but that kind
of obscures the fact that we actually do this because it's what works for the
two known applications of this method.  Maybe just a top-level comment on the
method that describe what it does?

         LayoutBox* containerBox = toLayoutBox(o);
         containerBox->applyCachedClipAndScrollOffsetForPaintInvalidation(rect);
         if (rect.isEmpty())