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View Full Version : shadow texture lookup always returns 0



strattonbrazil
11-18-2011, 08:36 AM
I'm trying to implement dual-paraboloid shadow mapping. The shadow maps I'm rendering look correct, but I believe something is wrong with my configuration because even if I change my GL_TEXTURE_COMPARE_FUNC to GL_ALWAYS, I still seem to get 0 back from my texture(...) function in GLSL.

Create two depth textures


// depth map setup
glGenTextures(2, depthMaps);
for (int i = 0; i < 2; i++) {
glBindTexture(GL_TEXTURE_2D, depthMaps[i]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_R_TO_TEXTURE );

// I would expect setting this to GL_ALWAYS, the texture(...) lookup in my
// GLSL code would always return 1 regardless of what I pass it
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
glBindTexture(GL_TEXTURE_2D, 0);
}


Render the scene from my light, setup the size/format of my texture, and copy my read buffer into it. I also do a glReadPixels(...) just to save my depth buffer off to a file to make sure its rendering correctly (light-projection setup correctly and reading from correct buffer).


renderSceneFromLight(...);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32, shadowXres, shadowYres, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, 0); checkGL("glteximage2d to depth texture");
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, shadowXres, shadowYres); checkGL("copytexsubimage2d to depth texture");
glReadPixels(0, 0, shadowXres, shadowYres, GL_DEPTH_COMPONENT, GL_FLOAT, pixels); checkGL("read pixels from depth buffer");


Finally, I render my scene from the camera-perspective perspective.


setupShader(...);
if (depthMaps != 0) {
QString depthMapNames[] = { "depthMapP", "depthMapN" };
for (int i = 0; i < 2; i++) {
glActiveTexture(GL_TEXTURE0+i);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, depthMaps[i]); checkGL("bind depth texture");
shader->setUniformValue(depthMapNames[i].toStdString().c_str(), depthMaps[i]); checkGL("set dm texture uniform");
std::cout << shader->uniformLocation(depthMapNames[i]) << std::endl; // valid locations returned
}
}
renderScene();


In my GLSL code I have the light intensity multiplied against the value returned from the texture(...) lookup. From what I can tell though, the value returned is always zero.


float res = 0.5;
if (alpha >= 0.5) { // user 1st hemisphere
res = texture(depthMapP, hemiShadowLookup0);
} else { // use 2nd hemisphere
res = texture(depthMapN, hemiShadowLookup1);
}
float lightIntensity = uniformLightIntensity * res;


I'm setting the uniform sampler values in the shader to the texture handles. I'm always confused if I should be passing them or the texture units. Passing the texture handles (generated by glGenTextures) doesn't raise an error from my GL error check, even though this documentation/example (binding samplers (http://www.opengl.org/wiki/GLSL_Sampler#Binding_textures_to_samplers)) seems to be passing texture units?

Anyway, maybe I'm misunderstanding something, but I thought that regardless of the contents of my shadow map or the texture coordinates passed to it, if the texture is setup/bound correctly (in C++ and in the shader) and the comparison function is set to GL_ALWAYS, it should always return 1, right?

Alfonse Reinheart
11-18-2011, 09:24 AM
I'm setting the uniform sampler values in the shader to the texture handles. I'm always confused if I should be passing them or the texture units.

Texture units.


Passing the texture handles (generated by glGenTextures) doesn't raise an error from my GL error check

That's probably because you only have a few textures and your implementation just so happens to allocate them starting at 1.

strattonbrazil
11-18-2011, 05:53 PM
I'm setting the uniform sampler values in the shader to the texture handles. I'm always confused if I should be passing them or the texture units.

Texture units.


Passing the texture handles (generated by glGenTextures) doesn't raise an error from my GL error check

That's probably because you only have a few textures and your implementation just so happens to allocate them starting at 1.

That was indeed my problem. Sending texture units (starting at 0 instead of GL_TEXTURE0) fixed the lookup issue. Thanks.