Re: Depth Buffer

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Rémi Arnaud (remi++at++remi.engr.sgi.com)
Thu, 25 Sep 1997 13:30:39 -0700 (PDT)

Paul Berridge wrote:
>
> Can anyone tell me how to calculate depth from the value stored in the
> depth buffer?
>
> I guessed that it would be something like:
>
> depth = nearClip*farClip/((1-dBuffVal)*farClip+dBuffVal*nearClip),
>
> which gives depth values between the near and far clip ranges, but the
> results aren't quite right.

 glReadPixels(x,y,1,1,GL_DEPTH_COMPONENT,GL_FLOAT,&f);
 z = 2*far*near / (far+near - (far - near) * (2 * f -1.));

 note that the ReadPixel function accuracy is 16bits linear integer,
 even if the Zbuffer is 23bits compressed.

>
> Alternatively, is there a Performer function I can call to calculate it
> for me?

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