[Mono-bugs] [Bug 80323][Nor] Changed - Incorrect ColorMatrix alpha processing

bugzilla-daemon at bugzilla.ximian.com bugzilla-daemon at bugzilla.ximian.com
Wed Dec 20 16:03:27 EST 2006

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Changed by sebastien at ximian.com.


--- shadow/80323	2006-12-20 14:17:26.000000000 -0500
+++ shadow/80323.tmp.16416	2006-12-20 16:03:27.000000000 -0500
@@ -113,6 +113,18 @@
 bitmap (which contains 255,255,155,155) [1] and this cause [2] a
 "fainter" color value to be drawn (255,255,255,255 instead of
 [1] this is ok and happens on both MS and Mono
 [2] this isn't correct and it's a bug
+------- Additional Comments From sebastien at ximian.com  2006-12-20 16:03 -------
+The alpha bug is that Cairo use pre-multipled alpha (where 50% red ==
+0x80800000 not 0x80ff0000) and Mono matrix-computed colors (RGB)
+weren't multiplied by A/255. This results in fainter colors (only)
+when alpha was used in the matrix, which wasn't checked by our test
+suite. I'll convert your test application into unit tests.
+This also seems to fix the blue background issue, but some flicker
+makes it hard to be 100% sure (I will do more tests, by outputing
+bitmap color values, to be sure).

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