Re: GL transparency/texturing question

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Mon, 18 Mar 1996 21:57:46 +0000

On Mar 18, 1:40pm, Mike Greene wrote:
> Subject: GL transparency/texturing question
>
> Sorry, that this is not a performer question, but I got no response on the
sgi-graphics
> newsgroup. I'm using GL on a High Impact. I'm trying to paste a tree texture
(RGBA) onto
> a transparent rectangle, hoping to show only the body of the tree , but not
the remainig

It's not the rectangle that's transparent it's the alpha information in the
tree image.

> portion of the rectangle. According to the GL manual , page 15-47, this
should
> be possible using msalpha and afunction, but they give no example. My
experience has the texture
> fading along with the rectangle as I lower the alpha. Does anyone have any
code snippets
> illustrating how to do this?

Again this suggests your applying alpha to the polygon rather than in the
texture. Your polygon alpha should be 1.0 (255) your image should contain alpha
= 0.0 (0) around the tree and 1.0 (255) where leaves & trunk are. It sounds
like you've got everything else correct since your tree fades with alpha.

>
> Thanks.
> **********************************************************
> Mike Greene '66 GT-350H
> Huntsville, AL '69 Mach 1 428SCJ
> greene++at++amtec-corp.com '70 Boss 302
> '69 Cobra 428CJ
> '93 SVT Cobra
> **********************************************************
>
>-- End of excerpt from Mike Greene

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