[webkit-reviews] review requested: [Bug 5909] overlapping element leaves trail when scrolling iframe (affects Gmail) : [Attachment 12985] check layer hierarchy for overlap

[bugzilla-request-daemon at macosforge.org]

Antti Koivisto <koivisto at iki.fi> has asked  for review:
Bug 5909: overlapping element leaves trail when scrolling iframe (affects
Gmail)
http://bugs.webkit.org/show_bug.cgi?id=5909

Attachment 12985: check layer hierarchy for overlap
http://bugs.webkit.org/attachment.cgi?id=12985&action=edit

------- Additional Comments from Antti Koivisto <koivisto at iki.fi>
Crawl the layer hierarchy for potential frame overlaps, use slow repaints if
something is found. It should handle common cases well and does not activate
slow repaints unnecessarily.

Check is done from frame paint() which is not too nice. Don't know where else
to put it, layer positioning is sort-of paint time thing. Caching could speed
it up in expense of added compexity. Not sure if it is really worthwhile.