Re: How do I overlay Performer scene on X window grafic context?

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Angus Dorbie (dorbie++at++sgi.com)
Mon, 15 Jun 1998 11:21:42 -0700

Scott McMillan wrote:
>
> ISOMURA_MITUGU wrote:
> >
> > I use X window + Motif.
> > I want to draw picture image(Ximage format) to Motif graphic context
> > and I want to overlay Performer scene on it.
> > And Performer image must be half transparent.
> > Please advise me how to do.
>
> Would it make any sense to draw the performer scene first and then
> render the image with alpha on top of the scene?

This would firstly require some destination alpha and some
pretty fancy x support.

How you do this depends on the type of visual you have. You may have
a colour map which would make the blending of one image with another
a bit of a nightmare.

Either way you'll probably have to read image from both buffers,
blend in software and then write the image.

If you use an OpenGL rendering context in the Motif window (it can be
done) then you could introduce 50% alpha to the performer image in
memory after you read from performer but before you glDrawPixels.
Then you can enable blending and drawpixels with source_alpha,
one_minus_source_alpha for the blend.

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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