[webkit-changes] [WebKit/WebKit] 3614ef: Web content renders blank on tab switch.

[mattwoodrow]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 3614ef890007d387d7a8dc9c809eb80d645c275b
      https://github.com/WebKit/WebKit/commit/3614ef890007d387d7a8dc9c809eb80d645c275b
  Author: Matt Woodrow <mattwoodrow at apple.com>
  Date:   2023-12-19 (Tue, 19 Dec 2023)

  Changed paths:
    M Source/WebKit/GPUProcess/graphics/RemoteImageBufferSet.cpp

  Log Message:
  -----------
  Web content renders blank on tab switch.
https://bugs.webkit.org/show_bug.cgi?id=266655
<rdar://119735082>

Reviewed by Simon Fraser.

m_previouslyPaintedRect is used to minimize the copy-forward rect when we know the new
front buffer is also previous-previous-front-buffer (N-2). In that case we only need to
copy the pixels drawn last time (into N-1), minus the pixel we're going to draw this time.

If the buffer is N-2, but it's been purged, then that also needs to skip the optimization,
so we clear m_previouslyPaintedRect.

* Source/WebKit/GPUProcess/graphics/RemoteImageBufferSet.cpp:
(WebKit::RemoteImageBufferSet::ensureBufferForDisplay):

Canonical link: https://commits.webkit.org/272304@main