Premultiplied alpha handle for driver

[Siarhei Siamashka]

On Tuesday 01 June 2010, Jonathan Morton wrote:
> On Mon, 2010-05-31 at 10:42 +0800, Huang, FrankR wrote:
> > We know the premultiplied alpha will be used sometimes in blend. Is
> > that used in the graphics driver?
>
> XRender always expects premultiplied alpha in images.  Your previous
> example, with ARGB values of (100,255,0,0) is therefore an invalid pixel
> vector, since the R channel is greater than the A channel.

This is not necessarily invalid. It's more like "additive blending" feature
which is even used by some people:
http://home.comcast.net/~tom_forsyth/blog.wiki.html#[[Premultiplied%20alpha]]

-- 
Best regards,
Siarhei Siamashka