Repaint non-stacking-context composited children when they scroll.

Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060
Committed: https://crrev.com/188d4f93b86d9640ccf1f05f85e08694e358fc14
Cr-Commit-Position: refs/heads/master@{#402612}

[skobes, 2016-06-28 20:11:41]

Patchset #1 (id:1) has been deleted

[skobes, 2016-06-28 20:11:48]

Patchset #1 (id:20001) has been deleted

[skobes, 2016-06-28 20:18:33]

The CQ bit was checked by skobes@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-06-28 20:20:01]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[skobes, 2016-06-28 21:36:12]

The CQ bit was checked by skobes@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-06-28 21:37:10]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[skobes, 2016-06-28 21:53:10]

Description was changed from

==========
Repaint non-stacking-context composited children when they scroll.

BUG=596060
==========

to

==========
Repaint non-stacking-context composited children when they scroll.

When a scroller is not using composited scrolling, PaintLayerScrollableArea must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with transforms.

BUG=596060
==========

[skobes, 2016-06-28 21:54:16]

Description was changed from

==========
Repaint non-stacking-context composited children when they scroll.

When a scroller is not using composited scrolling, PaintLayerScrollableArea must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with transforms.

BUG=596060
==========

to

==========
Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060
==========

[skobes, 2016-06-28 21:58:50]

skobes@chromium.org changed reviewers:
+ chrishtr@chromium.org, vollick@chromium.org

[chrishtr, 2016-06-28 22:33:06]

https://codereview.chromium.org/2107903002/diff/60001/third_party/WebKit/Sour...
File third_party/WebKit/Source/core/paint/PaintLayer.cpp (right):

https://codereview.chromium.org/2107903002/diff/60001/third_party/WebKit/Sour...
third_party/WebKit/Source/core/paint/PaintLayer.cpp:650: // negative z-index
descendants into an ancestor's GraphicsLayer.
Couldn't this happen for positive z-index also? What prevents that?

[skobes, 2016-06-28 22:55:53]

https://codereview.chromium.org/2107903002/diff/60001/third_party/WebKit/Sour...
File third_party/WebKit/Source/core/paint/PaintLayer.cpp (right):

https://codereview.chromium.org/2107903002/diff/60001/third_party/WebKit/Sour...
third_party/WebKit/Source/core/paint/PaintLayer.cpp:650: // negative z-index
descendants into an ancestor's GraphicsLayer.
On 2016/06/28 22:33:06, chrishtr wrote:
> Couldn't this happen for positive z-index also? What prevents that?

The child's normal flow and positive z-index content paints into the child's own
(main) GraphicsLayer.

PaintLayerPainter::paintLayerContents implements the conditional painting of
negative z-index content based on PaintLayerFlags.

[chrishtr, 2016-06-28 23:33:18]

lgtm

[commit-bot: I haz the power, 2016-06-28 23:36:26]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-06-28 23:36:27]

Dry run: This issue passed the CQ dry run.

[skobes, 2016-06-28 23:52:17]

The CQ bit was checked by skobes@chromium.org

[commit-bot: I haz the power, 2016-06-28 23:53:41]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-06-29 00:23:23]

Description was changed from

==========
Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060
==========

to

==========
Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060
==========

[commit-bot: I haz the power, 2016-06-29 00:23:24]

Committed patchset #2 (id:60001)

[commit-bot: I haz the power, 2016-06-29 00:26:14]

Description was changed from

==========
Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060
==========

to

==========
Repaint non-stacking-context composited children when they scroll.

When a PaintLayerScrollableArea is not using composited scrolling, it must
usually issue a paint invalidation for every scroll, but it can skip the
invalidation if all scrolling content is composited.  This optimization was
added by http://crrev.com/27239004.

However, one subtlety was not accounted for: a composited child that is not a
stacking context paints negative z-index content into the GraphicsLayer of the
nearest stacking-context ancestor.  If we have such a child, we must still issue
the invalidation.

Note that any any transform-related property creates a stacking context (see
call to setZIndex(0) in StyleAdjuster::adjustComputedStyle), so this will not
de-optimize scrollers that force compositing with translateZ(0) or similar.

BUG=596060

Committed: https://crrev.com/188d4f93b86d9640ccf1f05f85e08694e358fc14
Cr-Commit-Position: refs/heads/master@{#402612}
==========

[commit-bot: I haz the power, 2016-06-29 00:26:15]

Patchset 2 (id:??) landed as
https://crrev.com/188d4f93b86d9640ccf1f05f85e08694e358fc14
Cr-Commit-Position: refs/heads/master@{#402612}