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pallard

How to convert gl_FragDepth to real world depth ?

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Hi,

I am trying to generate a range image in a fragment shader.

I would like to know how to transform the gl_FragDepth (which is a non-linear transformed value of the actual range in the real world) to get the actual range ?

I have tried the following without success:

float MyLinearizeDepth(float z)
{
float n = 1.0; // camera z near
float f = 100.0; // camera z far
return (2.0 * n) / (f + n - z * (f - n));
}

I have used the FrontClipDistance for n and BackClipDistance (I am using JAVA3D) for f . I have my view set-up to look at a flat plane located 50 units in front of the camera. I get an actual range of 0.019 !

What I am doing wrong ?

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Would this not be easier by using gl_FragCoor?

The .z of that contains the window normal z, so you just need to add the near plane distance to it.

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gl_FragCoord.z is the depth value (0 to 1).
gl_FragDepth is a write-only value which lets you modify the depth written to the depth buffer.

http://www.opengl.org/sdk/docs/manglsl/xhtml/gl_FragCoord.xml
http://www.opengl.org/sdk/docs/manglsl/xhtml/gl_FragDepth.xml

To OP: from where did you come up with that equation? It could be right, but I just don't recognize it.

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