I am trying to implement cascaded shadow maps but I am having a strange issue with my FBO. As far as I can tell I am completely unable to write to the attached depth-texture. Even using glClear(GL_DEPTH_BUFFER_BIT) and trying various different clear values, I am unable to see any changes in the texture when I render it to the screen.

Here's a peek at some of my code:

bool CascadedShadowMap::Initialize(unsigned int WindowWidth, unsigned int WindowHeight)
{
m_width = WindowWidth;
m_height= WindowHeight;
 
    // Create the FBO
    glGenFramebuffers(1, &m_fbo);
 
    // Create the depth buffer
    glGenTextures(1, &m_shadowMap);
    glBindTexture(GL_TEXTURE_2D, m_shadowMap);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32, 2 * WindowWidth, 2 * WindowHeight, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, m_fbo);
    glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, m_shadowMap, 0);
 
    // Disable writes to the color buffer
    glDrawBuffer(GL_NONE);
 
 
    GLenum Status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
 
    if (Status != GL_FRAMEBUFFER_COMPLETE) {
        vDebugOut("error initializing shadow map! -CasadedShadowMap.cpp");
 
return false;
    }
 
    return true;
}
 

The debug message is not printed so I know the frame buffer is complete. I also made sure the function is being called.

Here's where the texture should be cleared:

 
void vGraphics::fillShadowTextureDirectionalCascadedMap()
{
 
m_noFragmentShader->enable();
 
glPushAttrib(GL_VIEWPORT_BIT);
 
cascaded_shadow_map->BindForWriting();
 
cascaded_shadow_map->Clear();
 
// Rendering models commented out for now. Trying to get Clear() to work.
/* 
...
*/
 
glPopAttrib();
 
m_noFragmentShader->disable();
}
 

[/code]

The methods "BindForReading" and "Clear" shown above are implemented like so:

 
void CascadedShadowMap::BindForWriting()
{
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, m_fbo);
}
 
void CascadedShadowMap::Clear()
{
glViewport(0, 0, 2* m_width, 2 * m_height);
glDepthMask(GL_TRUE);
glEnable(GL_DEPTH_TEST);
glDisable(GL_STENCIL_TEST);
glDrawBuffer(GL_NONE);
glDisable(GL_DEPTH_CLAMP);
glClearDepth(0.25f);
glClear(GL_DEPTH_BUFFER_BIT);
}
 

As you can see I'm setting a lot of options to try to make absolutely certain that nothing will prevent the GBuffer from getting cleared.

Now, just before my light pass, have:

m_dirLightShader->enable();
cascaded_shadow_map->BindForReading(7);
m_dirLightShader->setCascadedShadowUnit(7);

Here's the code for the two functions above.

void vDirectionalLightShader::setCascadedShadowUnit(GLuint textureUnit)
{
glUniform1i(m_unif_casc_shadow_map_id, textureUnit);
}
...
void  CascadedShadowMap::BindForReading(GLenum TextureUnit)
{
glEnable(GL_TEXTURE_2D);
    glActiveTexture(TextureUnit);
    glBindTexture(GL_TEXTURE_2D, m_shadowMap);
}

Now at the end of my fragment shader in my light pass (or "texture render pass" if you will):

 
float mapSample = (texture(gCascadedShadowMap, TexCoord).x);
 
FragColor =   vec4(mapSample,mapSample,mapSample,1);
 
}
 

first thing i'd check is if the texture you are writing to is somehow still bound, on ANY texture unit

can't think of anything else

I don't think thats it. I'm not using the texture for anything else.

(edit) Being doing more testing and it would appear that the depth clearing is being applied to my g-buffer (previously bound frame buffer) and not to the shadow FBO. I can't see why though, I am definitely binding the shadow FBO before clearing the depth buffer.

Fixed a small bug - I forgot to reset the glClearDepth to 1.0f after setting it to 0.25f. But still not working.

I think it has something to do with my gBuffer. My gBuffer has 4 color textures and a depth/stencil texture attached to its FBO. The shadow map FBO has only a depth texture attached. When I do my light pass I have my g-buffer fbo bound, and then I bind the shadow-map's shadow texture to an appropriate texture unit. It appears as if the gBuffer cannot "see" the shadow texture sitting in the unbound FBO. By my understanding I thought this would work but is there some technicality here that I'm not aware of?