Bug 100719 – [Qt] Rendering a scaled canvas with shadowBlur is incorrect and really slow

• Component: WebKit Qt
• Status: RESOLVED INVALID

Created attachment 171357 [details]
Screenshot and demo C++ Qt project

OS X version: 10.8.2
Qt version: 4.8.1

Load shadow-blur-test.html in a QWebView. It renders two identical red squares with a drop shadow. The left square has a scale of 1 and the right square has a scale of 0.01.

Expected:
Both the left and right renderings should look the same.

Instead:
The left rendering is rendered correctly but the right rendering only has a drop shadow along the vertical edges. In addition, rendering the right square takes 13 seconds vs 1 millisecond for the left square. It seems that QtWebKit renders the shadow at a huge resolution and then downsamples afterwards.

Workaround:
Don't use the canvas transform API and do all transforms manually instead.

[Jocelyn Turcotte]

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