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<TITLE> [Mono-osx] [Mono-winforms-list] DrawImage alpha blend broken in libgdiplus
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<H1>[Mono-osx] [Mono-winforms-list] DrawImage alpha blend broken in libgdiplus</H1>
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<B>Sebastien Pouliot</B>
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<A HREF="mailto:mono-osx%40lists.ximian.com?Subject=%5BMono-osx%5D%20%5BMono-winforms-list%5D%20DrawImage%20alpha%20blend%20broken%20in%0A%09libgdiplus&In-Reply-To=49DCC9FB.8070007%40yessoftware.com"
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TITLE="[Mono-osx] [Mono-winforms-list] DrawImage alpha blend broken in libgdiplus">sebastien.pouliot at gmail.com
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</A><BR>
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<I>Wed Apr 8 13:33:43 EDT 2009</I>
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<!--beginarticle-->
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<PRE>Hello Alex,
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The patch looks good. However this kind of fix has been known to cause
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regression in the past.
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Could you supply unit tests that ensure that the image can be saved and
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reloaded correctly ? (modifying your previous sample code should be
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easy).
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With this (and if all existing tests pass successfully) I'll be able to
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commit your patch.
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Thanks!
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Sebastien
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On Wed, 2009-04-08 at 18:59 +0300, Alex Shulgin wrote:
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><i> Alex Shulgin wrote:
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</I>><i> > Hi,
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</I>><i> >
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</I>><i> > I believe that alpha blending is broken in libgdiplus.
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</I>><i>
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</I>><i> I've located the problem. It is due to the inconsistent handling of
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</I>><i> PixelFormat32bppPArgb (premultiplied alpha) in libgdiplus.
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</I>><i>
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</I>><i> In the attached patch I've added the check on PArgb to DrawImageRect in
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</I>><i> analogy with texturebrush.c and fixed pngcodec.c to set pixel format to
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</I>><i> PArgb if premultiplication was done.
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</I>><i>
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</I>><i> This fixes my demo program and there's no visible regressions in a
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</I>><i> fairly complex application which originally revealed the problem.
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</I>><i>
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</I>><i> If the feeling is such that this is appropriate patch, I'd add the same
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</I>><i> handling for places like this (there's few).
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</I>><i>
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</I>><i> --
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</I>><i> Regards,
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</I>><i> Alex
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</I>><i>
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</I>><i> _______________________________________________
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</I>><i> Mono-winforms-list maillist - <A HREF="http://lists.ximian.com/mailman/listinfo/mono-osx">Mono-winforms-list at lists.ximian.com</A>
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</I>><i> <A HREF="http://lists.ximian.com/mailman/listinfo/mono-winforms-list">http://lists.ximian.com/mailman/listinfo/mono-winforms-list</A>
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</I>
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</PRE>
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