Depth texture white in shader

Question

I am trying to implement shadow mapping into my project and am stuck at this problem: If I'm reading the shadow map values with glReadPixels and linearize those values, I am getting exactly the value I was looking for: ranging from 0 to 1. But when I am doing the exact same calculation in my shader, everything, where I rendered an object, is white. Another thing I noticed(which i assume is directly linked to my problem) is that if I am changing glClearDepth to anything different than 1, the output of my shader is black and the output of glReadPixels after linearizing is not anymore the value I wanted but anything else.

Here is the code where I am creating the depth texture:

glBindTexture(GL_TEXTURE_2D, _textures[GBTEXTURE_DEPTH]);  
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, width, height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE);

glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, _textures[GBTEXTURE_DEPTH], 0);

And here is the fragment shader:

in vec2 fragUV;
uniform sampler2D tex;

float zfar = 1000.0f;
float znear = 1.0f;

float linearize(float depth)
{
    return (-zfar * znear / (depth * (zfar - znear) - zfar)) / zfar;
}

out vec4 finalColor;
void main(void){
    float depth = texture2D(tex, fragUV).r;
    depth = linearize(depth);

    finalColor = vec4(depth);
}

I am doing the exact same calculation on the CPU, with correct values as a result.

I hope I described my problem with enough details for you to help me.

Answer 1

Make sure that you call glEnable(GL_DEPTH_TEST) when you are binding your depth buffer for rendering. Preferably just before you call glBindFramebuffer(GL_FRAMEBUFFER, (GLuint)Index);