Cubemap shadow mapping not working

Question

I\'m attempting to create omnidirectional/point lighting in openGL version 3.3. I\'ve searched around on the internet and this site, but so far I have not been able to accomplis

Answer 1

If you leave the fragment depth to OpenGL to determine you can take advantage of hardware hierarchical Z optimizations. Basically, if you ever write to gl_FragDepth in a fragment shader (without using the newfangled conservative depth GLSL extension) it prevents hardware optimizations called hierarchical Z. Hi-Z, for short, is a technique where rasterization for some primitives can be skipped on the basis that the depth values for the entire primitive lies behind values already in the depth buffer. But it only works if your shader never writes an arbitrary value to gl_FragDepth.

If instead of writing a fragment's distance from the light to your cube map, you stick with traditional depth you should theoretically get higher throughput (as occluded primitives can be skipped) when writing your shadow maps.

Then, in your fragment shader where you sample your depth cube map, you would convert the distance values into depth values by using a snippet of code like this (where f and n are the far and near plane distances you used when creating your depth cube map):

float VectorToDepthValue(vec3 Vec)
{
    vec3 AbsVec = abs(Vec);
    float LocalZcomp = max(AbsVec.x, max(AbsVec.y, AbsVec.z));

    const float f = 2048.0;
    const float n = 1.0;
    float NormZComp = (f+n) / (f-n) - (2*f*n)/(f-n)/LocalZcomp;
    return (NormZComp + 1.0) * 0.5;
}

Code borrowed from SO question: Omnidirectional shadow mapping with depth cubemap

So applying that extra bit of code to your shader, it would work out to something like this:

void main () {
    float shadowDepth = texture(shadowMap, ShadowCoord.xyz/ShadowCoord.w).x;
    float testDepth   = VectorToDepthValue(lightPos - PositionWorldSpace);
    if (shadowDepth < testDepth)
        visibility = 0.1;
}