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List:       webkit-changes
Subject:    [webkit-changes] [WebKit/WebKit] 77e5bb: Corrupt tiles when scrolling and selecting text qu...
From:       mattwoodrow <noreply () github ! com>
Date:       2024-01-31 18:33:26
Message-ID: WebKit/WebKit/push/refs/heads/main/14b3ba-77e5bb () github ! com
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  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 77e5bb39107371558f6ee94cf74b988d3231ab41
      https://github.com/WebKit/WebKit/commit/77e5bb39107371558f6ee94cf74b988d3231ab41
  Author: Matt Woodrow <mattwoodrow@apple.com>
  Date:   2024-01-31 (Wed, 31 Jan 2024)

  Changed paths:
    A LayoutTests/compositing/repaint/needs-no-display-volatile-repaint-expected.html
    A LayoutTests/compositing/repaint/needs-no-display-volatile-repaint.html
    M Source/WebKit/GPUProcess/graphics/RemoteRenderingBackend.cpp

  Log Message:
  -----------
  Corrupt tiles when scrolling and selecting text quickly.
https://bugs.webkit.org/show_bug.cgi?id=268430
<rdar://121934201>

Reviewed by Simon Fraser.

If ensureBufferForDisplay returns SwapBuffersDisplayRequirement::NeedsNoDisplay, then we don't want
to call prepareForDisplay. The latter copies pixels from the old front buffer into the new one,
and when no display is required there wasn't a front/back swap, so no copy needed.

This caused issues because we also set 'm_previouslyPaintedRect` to the (empty!) dirty area,
effectively recording that the front and back buffers were identical, despite it likely
not being true. The next attempt to paint these buffers would omit a back-to-front copy,
thinking the buffers were identical, and then we'd do a partial update on top of stale content.

This happens when scrolling, since scrolling tiles get pooled (and made volatile), then
recycled.

* LayoutTests/compositing/repaint/needs-no-display-volatile-repaint-expected.html: Added.
* LayoutTests/compositing/repaint/needs-no-display-volatile-repaint.html: Added.
* Source/WebKit/GPUProcess/graphics/RemoteRenderingBackend.cpp:
(WebKit::RemoteRenderingBackend::prepareImageBufferSetsForDisplay):
(WebKit::RemoteRenderingBackend::prepareImageBufferSetsForDisplaySync):

Canonical link: https://commits.webkit.org/273838@main


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