GLSL - Incorrect results when retrieving values from shadow cubemap - c++

Question

When using cubemaps I'm getting inconsistent results in my shaders as opposed to my program.
For testing purposes I wrote a test-program that simply creates a depth cubemap texture and writes '1' to all sides of it:
unsigned int frameBuffer;
glGenFramebuffers(1,&frameBuffer);
unsigned int texture;
glGenTextures(1,&texture);
glBindFramebuffer(GL_FRAMEBUFFER,frameBuffer);
glBindTexture(GL_TEXTURE_CUBE_MAP,texture);
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_DEPTH_TEXTURE_MODE,GL_LUMINANCE);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_COMPARE_FUNC,GL_LEQUAL);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_COMPARE_MODE,GL_COMPARE_R_TO_TEXTURE);
unsigned int width = 512;
unsigned int height = 512;
for(unsigned int i=0;i<6;i++)
{
glTexImage2D(
GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,
0,
GL_DEPTH_COMPONENT16,
width,height,
0,GL_DEPTH_COMPONENT,
GL_FLOAT,
0
);
glFramebufferTexture2D(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,texture,0);
}
unsigned int status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if(status != GL_FRAMEBUFFER_COMPLETE)
return;
float *data = new float[width *height];
for(unsigned long long i=0;i<(width *height);i++)
data[i] = 1.f;
for(unsigned int i=0;i<6;i++)
{
glTexSubImage2D(
GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,
0,
0,
0,
width,height,
GL_DEPTH_COMPONENT,
GL_FLOAT,
&data[0]
);
}
delete[] data;
// Check to see if data has been written correctly
data = new float[width *height];
for(unsigned int i=0;i<6;i++)
{
glFramebufferTexture2D(GL_READ_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,texture,0);
glReadPixels(0,0,width,height,GL_DEPTH_COMPONENT,GL_FLOAT,&data[0]);
for(unsigned long long j=0;j<(width *height);j++)
{
if(data[j] != 1.f)
return;
}
}
delete[] data;
// Check end
Rendering:
float screenVerts[18] = {
-1.f,-1.f,0.f,
1.f,-1.f,0.f,
-1.f,1.f,0.f,
-1.f,1.f,0.f,
1.f,-1.f,0.f,
1.f,1.f,0.f
};
unsigned int vertexBuffer;
glGenBuffers(1,&vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);
glBufferData(GL_ARRAY_BUFFER,sizeof(float) *18,&screenVerts[0],GL_STATIC_DRAW);
glUseProgram(shader);
glBindTexture(GL_TEXTURE_CUBE_MAP,texture);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);
glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,(void*)0);
glDrawArrays(GL_TRIANGLES,0,6);
glDisableVertexAttribArray(0);
Vertex Shader:
#version 330 core
layout(location = 0) in vec3 vertPos;
out vec2 UV;
void main()
{
gl_Position = vec4(vertPos,1);
UV = (vertPos.xy +vec2(1,1)) /2.0;
}
Fragment Shader:
#version 330 core
in vec2 UV;
out vec3 color;
uniform samplerCubeShadow testShadow;
void main()
{
color.r = texture(testShadow,vec4(0,0,1,1));
// Just grab the value from a random direction and put it out as red color
}
(I've ported the C++ code from another language, so if you find some syntax errors in there, don't mind those, they're not in the actual code)
glGetError() does not return any errors.
ReadPixels proves that the writing process worked, however the result is a black screen. That means that the texture-call inside the shader returns 0, which should be impossible regardless of what I use as the direction vector.
What am I missing?

Answer 1

You consistently have the arguments for the glBind*() calls reversed. They all take a target as the first argument, and the object id (aka name) as the second argument. Instead of this:
glBindFramebuffer(frameBuffer,GL_FRAMEBUFFER);
glBindTexture(texture,GL_TEXTURE_CUBE_MAP);
glBindBuffer(vertexBuffer,GL_ARRAY_BUFFER);
It should be this:
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
glBindTexture(GL_TEXTURE_CUBE_MAP, texture);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
There are multiple instances of some of these in the code, so make sure that you catch them all.
Other than that, if this is the complete code, you're not rendering to the screen. You have an FBO without color attachment bound, so the output goes nowhere. If you want to render to the screen, you'll need to unbind the FBO:
glBindFramebuffer(GL_FRAMEBUFFER, 0);
You're also leaving the g and b components of the fragment output undefined, since you only write to r.