Paint very slow when horizontally resizing (CSS gradient)

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[James Robinson]

When viewing the page: http://www.apple.com/safari/features.html vertical resizes are taking a very long time (500ms+, sometimes multiple seconds) which causes the entire browser to seize up, the window to go white, etc.  

Instrumentation points to the time being spent in ScrollView::paint() and children.  Layout time is very very short, it appears there's something horrible going on in the rasterizing code.

This behavior appears on the Windows and Mac WebKit nightlies, Safari 4 beta on Windows and Mac, and in the Chromium port.

[Cameron Zwarich (cpst)]

A similar thing occurs with full-screen zoom.

[Mark Rowe (bdash)]

<rdar://problem/6618196>

[James Robinson]

Created attachment 27932 [details]
Reduced testcase

The critical bits are:

*) background: -webkit-gradient
*) lots of text on a fixed-width element
*) resizing the window to smaller than the width of the text-containing element, forcing a clip.

It appears to perform worse on OS X compared to Safari 4 beta on Windows or Chromium.

Created attachment 27941 [details]
Another reduction

A smaller reduction. The border is critical.

The problem seems to happen when Image::drawTiled() chooses to call GeneratedImage::drawPattern() instead of GeneratedImage::draw(), namely when the destination rect is not contained in the tile rect. GeneratedImage::drawPattern() proceeds to allocate a potentially huge image buffer, draw into it, create an image out of it (copying the data in the process), and then use that image as a pattern.

Created attachment 27996 [details]
Intersect the destination rect passed to darwTiledImage() with the dirty rect

Comment on attachment 27996 [details]
Intersect the destination rect passed to darwTiledImage() with the dirty rect

Going to add a test case

Created attachment 27997 [details]
Intersect the destination rect passed to darwTiledImage() with the dirty rect

[Simon Fraser (smfr)]

Comment on attachment 27997 [details]
Intersect the destination rect passed to darwTiledImage() with the dirty rect

r-me

Fixed in <http://trac.webkit.org/changeset/41238>. See also bug 24178.

[Simon Fraser (smfr)]

*** Bug 24956 has been marked as a duplicate of this bug. ***