[Webkit-unassigned] [Bug 193108] [ Mojave WK1 ] Some Image tests are flakey failures and are failing in tandem with zoomed in or blank image results

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=193108

Said Abou-Hallawa <sabouhallawa at apple.com> changed:

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                 CC|                            |sabouhallawa at apple.com

--- Comment #7 from Said Abou-Hallawa <sabouhallawa at apple.com> ---
This bug is happening because of a bug in CGWindowListCreateImage() in which it returns the wrong size snapshot when changing the window deviceScaleFactor from 2 to 1.

When running DRT, the bug happens only when running a hidpi test followed by a composite layout test. To fake the hipdi the deviceScaleFactor is set manually to 2. Before running a new test, the deviceScaleFactor has to be set back to 1. But this does not make CGWindowListCreateImage() works correctly in this case.

When createBitmapContextFromWebView() calls CGContextDrawImage(), only the bottom left quarter snapshot is drawn from the snapshot image to the bitmapContext. Most of the layout tests do not draw in this part of the WebView. So the result is seen as blank.

Like what we did in WebViewImpl::takeViewSnapshot() as a workaround for <rdar://problem/17084993>, we have to do similar workaround for DRT function createBitmapContextFromWebView().

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