[webkit-changes] [WebKit/WebKit] 2a5bd0: Make ::backdrop renderers use background layers wh...

[Tim Nguyen]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 2a5bd0ff38736fcfe4df01b8098012b8d0a1fbff
      https://github.com/WebKit/WebKit/commit/2a5bd0ff38736fcfe4df01b8098012b8d0a1fbff
  Author: Tim Nguyen <ntim at apple.com>
  Date:   2022-12-07 (Wed, 07 Dec 2022)

  Changed paths:
    M LayoutTests/TestExpectations
    M LayoutTests/compositing/no-compositing-when-full-screen-is-present-expected.txt
    M LayoutTests/compositing/no-compositing-when-full-screen-is-present.html
    M LayoutTests/fullscreen/full-screen-layer-dump-expected.txt
    M LayoutTests/fullscreen/full-screen-layer-dump.html
    M LayoutTests/platform/gtk/compositing/no-compositing-when-full-screen-is-present-expected.txt
    M Source/WebCore/rendering/RenderElement.cpp
    M Source/WebCore/rendering/RenderLayerBacking.cpp
    M Source/WebCore/rendering/RenderLayerCompositor.cpp
    M Source/WebCore/rendering/RenderObject.h

  Log Message:
  -----------
  Make ::backdrop renderers use background layers when possible
https://bugs.webkit.org/show_bug.cgi?id=248148
rdar://102566049

Reviewed by Simon Fraser.

Right now, when rotating in fullscreen on iPad, there are white gaps around the edges. This was avoided by RenderFullscreen using
"background layers" that are 3x the size with a negative offset. Now that RenderFullscreen is gone, we need to target ::backdrop
pseudo elements that have:

- The same rect as the RenderView
- position: fixed, since position: absolute can allow scrolling away from the ::backdrop, since the containing block is the ICB
- No transforms/clips/masks (since they intentionally do not cover the whole screen)

Also clean up remainders of RenderFullscreen which has been removed in 255641 at main.

* LayoutTests/compositing/no-compositing-when-full-screen-is-present-expected.txt:
* LayoutTests/compositing/no-compositing-when-full-screen-is-present.html:
* LayoutTests/platform/gtk/compositing/no-compositing-when-full-screen-is-present-expected.txt:
Update test expectations to reflect that ::backdrop is now layer backed in fullscreen.

* LayoutTests/TestExpectations:
* LayoutTests/fullscreen/full-screen-layer-dump-expected.txt:
* LayoutTests/fullscreen/full-screen-layer-dump.html:
Make test expectation more clear in the description to avoid regressing this test again, and update test expectation to reflect that "background layers" now work again.

* Source/WebCore/rendering/RenderElement.cpp:
(WebCore::RenderElement::propagateStyleToAnonymousChildren):
* Source/WebCore/rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::RenderLayerBacking):
* Source/WebCore/rendering/RenderLayerCompositor.cpp:
(WebCore::isDescendantOfFullScreenLayer):
Consider the fullscreen element's associated ::backdrop as fullscreen layer, otherwise the renderer is never layer-backed meaning we can't use "background layers".
We avoid backing non-fullscreen layers to optimize for power usage.

* Source/WebCore/rendering/RenderObject.h:
(WebCore::RenderObject::isAttachment const):
(WebCore::RenderObject::isAnonymousBlock const):
(WebCore::RenderObject::isRenderFullScreen const): Deleted.
(WebCore::RenderObject::isRenderFullScreenPlaceholder const): Deleted.

Canonical link: https://commits.webkit.org/257538@main