Re: Alpha information in lrectwrite

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Tue, 23 Apr 1996 16:50:03 +0100

On Apr 23, 4:21pm, Morten Eriksen wrote:
> Subject: Alpha information in lrectwrite
> I'm fiddling around with the lrectwrite() function to try to make the
> alpha component of the color values work correctly. No combination of
> zfunction(), zwritemask() and zbuffer() seems to work for me, so my
> question is how should I set the state of GL to make the alpha
> component work?

blendfunction is what you need.

> And how is the alpha component connected to the level
> of transparency (is 0x00 or 0xff complete transparency?)?
>

Depends on your blendfunction parameters. Usually 0x00 is transparent &
blendfunction (BF_SA, BF_MSA) is used. This would reverse if you switched the
blendfunction arguments. You have lots of flexibility to do lots of things with
your blendfunction.

> What I want to do is basically have a cursor drawn, over the 3D
> graphics, in PostDraw() with some completely transparent areas.
>
> Regards,
> Morten Eriksen
>
>-- End of excerpt from Morten Eriksen

-- 
Angus Dorbie,
The Reality Centre,
Silicon Graphics Ltd, UK
dorbie++at++reading.sgi.com

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