Avoid using backing store for compositing layers that just need to clip

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Simon Fraser (smfr)]

If an element becomes composited because it clips a composited child, then we currently draw it into backing store (a flashy tiled layer if necessary). We should just draw it into the window background of we can.

[Simon Fraser (smfr)]

<rdar://problem/5667730>

[Simon Fraser (smfr)]

Created attachment 137188 [details]
Patch

[WebKit Review Bot]

Comment on attachment 137188 [details]
Patch

Attachment 137188 [details] did not pass chromium-ews (chromium-xvfb):
Output: http://queues.webkit.org/results/12402479

New failing tests:
compositing/geometry/preserve-3d-switching.html
compositing/backing/no-backing-for-perspective.html
compositing/backing/no-backing-for-clip-overlap.html
compositing/overflow/overflow-positioning.html
compositing/backing/no-backing-for-clip.html

[WebKit Review Bot]

Created attachment 137210 [details]
Archive of layout-test-results from ec2-cr-linux-04

The attached test failures were seen while running run-webkit-tests on the chromium-ews.
Bot: ec2-cr-linux-04  Port: <class 'webkitpy.common.config.ports.ChromiumXVFBPort'>  Platform: Linux-2.6.35-28-virtual-x86_64-with-Ubuntu-10.10-maverick

[Dean Jackson]

Comment on attachment 137188 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=137188&action=review

r+ assuming test failures are misleading or updated.

> Source/WebCore/rendering/RenderLayerCompositor.cpp:1363
> +        || renderer->isTransparent() || renderer->hasMask() || renderer->hasReflection() || renderer->hasFilter()

I'd prefer these on separate lines just because every other test is, but I don't really care.

[Simon Fraser (smfr)]

http://trac.webkit.org/changeset/114283

[Adrienne Walker]

(In reply to comment #6)
> http://trac.webkit.org/changeset/114283

So, I'm confused.  The test failures were neither misleading nor updated.   How did this get checked in without fixing that?

Unsurprisingly, this exact same set of tests is now failing on the Chromium bots:  http://trac.webkit.org/changeset/114303/trunk/LayoutTests/platform/chromium/test_expectations.txt

[Simon Fraser (smfr)]

All of the compositing tests pass on Mac.

> compositing/geometry/preserve-3d-switching.html

This needs to be rebaselined for chromium.

> compositing/backing/no-backing-for-perspective.html
> compositing/backing/no-backing-for-clip-overlap.html
> compositing/backing/no-backing-for-clip.html

For some reason chromium has different layer sizes than Mac, I've no idea why. I suggest adding platform-specific results.

> compositing/overflow/overflow-positioning.html

This looks like a colorspace change.