[Webkit-unassigned] [Bug 25956] Canvas' composition is incorrect when alpha=0

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri May 22 00:53:30 PDT 2009


hamaji at chromium.org changed:

           What    |Removed                     |Added
  Attachment #30577|                            |review?
               Flag|                            |

------- Comment #2 from hamaji at chromium.org  2009-05-22 00:53 PDT -------
(From update of attachment 30577)
This is the reason why I introduced failing test cases in the previous patch:


This optimization was introduced 3 years ago. At this time, fillRect() always
calls fillRectSourceOver() so that this optimization was OK. So, I guess the
current behavior (when alpha is zero, all fillrect operations are skipped even
if the composite mode is 'copy') is not intentional.


Fortunately, Skia has the similar optimization path inside Skia and Skia checks
the composition mode if it is safe to do this optimization. I don't know if CG
has similar logic, but anyway I think this patch won't reduce performance
significantly as alpha=0 cases may be rare.

I also made error messages of the layout test case better, and added test case
for path and fill.

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