[whatwg] [canvas] globalCompositeOperation poorly defined
L. David Baron
dbaron at dbaron.org
Thu Jun 22 18:50:39 PDT 2006
The values of globalCompositeOperation are very poorly defined:
http://www.whatwg.org/specs/web-apps/current-work/#globalcompositeoperation
Some math is probably needed; prose alone seems unlikely to be
sufficient.
I made a quick test at:
http://dbaron.org/tests/canvas/composite-operations
Trunk Mozilla and Opera 9 do not interoperate on at least the following
(ignoring differences that could be attributed to rounding):
source-atop
source-over (the default!)
destination-atop
lighter
darker
xor
(Safari seems to show the colors as either random noise (latest for
10.3/PPC) or blank (latest for 10.4/Intel).)
Looking at Mozilla's code, it implements "copy" and "source-over" as the
same thing; from the code I'd guess that "source-over" was the incorrect
one, and this test seems to agree.
-David
--
L. David Baron <URL: http://dbaron.org/ >
Technical Lead, Layout & CSS, Mozilla Corporation
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available
URL: <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/attachments/20060622/aca43799/attachment-0001.pgp>
More information about the whatwg
mailing list