For reference, I've been working to get local and solid color backgrounds painted onto the scrolling contents layer so that we can promote them to layers while maintaining LCD text, see  issue 381840  / https://chromium.googlesource.com/chromium/src/+/9a2cdc8d96d94c736eb5547a7c8c541e58e5759f

Looking into this.

chrishtr@ did some recent work that could be related, see http://crrev.com/2241663002 and comment in LayoutBox.cpp:1040 and PaintInvalidationState.cpp:322 --

// This won't work fully correctly for fixed-position elements, who should receive CSS clip but for whom the current object
// is not in the containing block chain.

Continuing to look.

The comment is about css clip not applied for fixed-position elements when calculating visual rect. It should only cause over-paint-invalidation, but not corrupted rendering.

The visual rect for drawing the background doesn't look right:

{index: 1, client: "0x1860f024248 LayoutBlockFlow DIV id='scroller'", type: "DrawingBoxDecorationBackground", rect: [10.000000,10.000000 185.000000x550.000000], cacheIsValid: true, visualRect: [-10,-10 220x220]},

Sounds like the problem. This is it painting the background into the scrolling contents layer which extends beyond the overflow clip. Where does the visual rect come from?

For non-frame composited scrollers, these changes have some history on visual rect implementation:
http://crrev.com/1844993002
http://crrev.com/1830333002

As an overview, visual rects are obtained via DisplayItemClient::visualRect. In the common case we delegate to the previous paint invalidation rect, see LayoutObject::visualRect(), but there are special cases such as PageOverlay, LinkHighlight, InlineBox, and for scrollable areas as above we made the GraphicsLayer the DisplayItemClient and thus the provider of the visual rect.

There's also some scroller specific stuff around offsetFromLayoutObject:

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp?sq=package:chromium&dr=C&rcl=1471447605&l=443

It looks like the visual rect is getting clipped by the visible area somehow, hmm. 

BoxPainter is specialized for the case where it's painting the background of a paint container into a scrolling contents layer (which I assume is implicitly composited, see BoxPainter::isPaintingBackgroundOfPaintContainerIntoScrollingContentsLayer).

Given that, I am wondering whether in that case we should use the scrolling contents GraphicsLayer as the DisplayItemClient for the background drawing. This would produce the correct bounds. Conceptually this seems reasonable to me, but it's possible there's something I am missing around how composited scrolling is intended to be structured. In any case that background drawing seems like it should have a visual rect sized to the graphics layer size. I'm trying it now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ff27367de0553a7aa38f078e528d19024f2d3668

commit ff27367de0553a7aa38f078e528d19024f2d3668
Author: wkorman <wkorman@chromium.org>
Date: Sat Aug 20 16:58:14 2016

Fix visual rect for background box painting in composited scrollers.

Use the scrolling contents GraphicsLayer as the DisplayItemClient for the
background drawing when we're painting the full background of a composited
scroller.

BUG= 638611 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2254893005
Cr-Commit-Position: refs/heads/master@{#413340}

[modify] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/fast/repaint/overflow-scroll-local-background-text-color-change-expected.png
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/fast/repaint/overflow-scroll-local-background-text-color-change-expected.txt
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/fast/repaint/overflow-scroll-local-background-text-color-change.html
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/fast/scroll-behavior/overflow-scroll-with-local-background-and-text-expected.html
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/fast/scroll-behavior/overflow-scroll-with-local-background-and-text.html
[add] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/paint/invalidation/composited-overflow-with-local-background-expected.png
[modify] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/paint/invalidation/composited-overflow-with-local-background-expected.txt
[modify] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/LayoutTests/paint/invalidation/composited-overflow-with-local-background.html
[modify] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
[modify] https://crrev.com/ff27367de0553a7aa38f078e528d19024f2d3668/third_party/WebKit/Source/core/paint/BoxPainter.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/85b6016cab181514b75fe888f2648b3b70bdd1fe

commit 85b6016cab181514b75fe888f2648b3b70bdd1fe
Author: Rebaseline Bot <blink-rebaseline-bot@chromium.org>
Date: Sat Aug 20 17:58:15 2016

Auto-rebaseline for r413340

https://chromium.googlesource.com/chromium/src/+/ff27367de

BUG= 638611 
TBR=wkorman@chromium.org

Review URL: https://codereview.chromium.org/2254733014 .

Cr-Commit-Position: refs/heads/master@{#413342}

[modify] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/fast/repaint/overflow-scroll-local-background-text-color-change-expected.txt
[rename] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/linux/fast/repaint/overflow-scroll-local-background-text-color-change-expected.png
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/linux/fast/repaint/overflow-scroll-local-background-text-color-change-expected.txt
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/mac-mac10.9/fast/repaint/overflow-scroll-local-background-text-color-change-expected.png
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/mac-mac10.9/paint/invalidation/composited-overflow-with-local-background-expected.png
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/mac/fast/repaint/overflow-scroll-local-background-text-color-change-expected.png
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/mac/paint/invalidation/composited-overflow-with-local-background-expected.png
[add] https://crrev.com/85b6016cab181514b75fe888f2648b3b70bdd1fe/third_party/WebKit/LayoutTests/platform/win/fast/repaint/overflow-scroll-local-background-text-color-change-expected.png

Tested the issue on Latest Chrome# 54.0.2837.0 on Windows, Mac and Linux and is working as intended. Hence adding TE-Verified Labels.

Also attaching screenshot for further reference.
Thank You.

Deleted: 638611.jpg 37.0 KB

	638611.jpg 37.0 KB View Download