[Webkit-unassigned] [Bug 260505] New: [CoordinatedGraphics] Incomplete rendering after 10s inactivity without hardware acceleration

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=260505

            Bug ID: 260505
           Summary: [CoordinatedGraphics] Incomplete rendering after 10s
                    inactivity without hardware acceleration
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKit2
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: tomoki.imai at sony.com
                CC: kkinnunen at apple.com

Created attachment 467379

  --> https://bugs.webkit.org/attachment.cgi?id=467379&action=review

The reproduction steps using WebKitGTK MiniBrowser

Test Environment:
- Ubuntu 22.04
- webkit 267033 at main (https://github.com/WebKit/WebKit/commit/718ac9d)

Steps:
- Launch WebKitGTK MiniBrowser
- Make "Hardware Accelerated Policy" "never" from the preferences
- Navigate to https://webkit.org/
- Scroll down to the bottom of page (where there is no animation displayed)
- Focus to another window (for example terminal application)
- Wait 10s
- Focus MiniBrowser again

Actual Result:
- The content of website disappears.

Expected Result:
- The content of website should be displayed.

Our Invesitgation Note:
This seems to be a regression from 263118 at main (bug 255392). The backing store is discarded and not properly recovered.
There was another fix 266511 at main but unfortunately it doesn't fix the issue completely.

We see the same issue on WinCairo if it is configured to use DrawingAreaProxyCoordinatedGraphics. The default one is DrawingAreaProxyWC so it doesn't reproduce the issue without settings.

https://github.com/WebKit/WebKit/blob/1d5fbefb714166eebf47d4b06477332bb39b3a32/Source/WebKit/UIProcess/win/PageClientImpl.cpp#L57-L60

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