[Mono-winforms-list] Patch for bug 426305

Dick Porter dporter at codicesoftware.com
Thu Mar 31 14:26:07 EDT 2011

On 31/03/2011 7:24PM, Sebastien Pouliot wrote:
> On Thu, 2011-03-31 at 17:00 +0100, Dick Porter wrote:
>> Hi all
>> I've just added a patch to
>> https://bugzilla.novell.com/show_bug.cgi?id=426305 and am copying it
>> here too for review.
>> It removes the premultiplication when loading PNGs, as no other image
>> format does the same.  It then adds premultiplication when calling
>> assorted Draw*() functions in image.c, except when the graphics context
>> is a memory bitmap (so that if an image is drawn onto another image, it
>> doesn't get premultiplied multiple times.)
>  From the little I recall of the issue it makes sense (but will affect
> performance) to delay the pre-multiplication.
> The other way would be to keep a flag about the state of each image (and
> handle saving correctly, i.e. de-multiplication).

I tried adding a flag to the PNG image when it was loaded, to say that 
it was already premultiplied.  However, it seemed that the image_flags 
got lost along the way when images were manipulated.

I may of course be wrong about that, as I hadn't thought of the image on 
image drawing at that point.

- Dick

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