Render depth from framebuffer texture

Question

I've been trying to add SSAO (based on the tutorial here: http://john-chapman-graphics.blogspot.co.nz/2013/01/ssao-tutorial.html) to a project of mine and I've gotten stuck on rendering the depth correctly.

I have created a framebuffer texture to draw the depth to each frame. The texture itself looks correct when I draw it to a quad but I can't figure out how to correctly apply it to the whole scene.

Here's what the regular scene looks like:

And here's the applied depth texture:

Currently in my fragment shader I just use my regular texture coordinates (TexCoord0) to draw the depth texture. I'm guessing I need to change this but I don't have a clue what to change it to. Here's the relevant fragment shader code:

#version 330 core

in vec2 TexCoord0;

smooth in vec3 vNormal;
smooth in vec3 vWorldPos;
in mat4 ProjectionMatrix;

uniform sampler2D uDepthTex;

layout(location = 0) out vec4 FragColor;

void main()
{
    FragColor = texture(uDepthTex, TexCoord0);
}

I'm at a bit of a loss as to how to fix this. I've read a lot of sample code online which seems to use regular texture coordinates to draw the depth.

EDIT: Here's my framebuffer setup code:

glGenFramebuffers(1, &ssaoFramebufferID);
glBindFramebuffer(GL_FRAMEBUFFER, ssaoFramebufferID);

glGenTextures(1, &ssaoDepthTextureID);
glBindTexture(GL_TEXTURE_2D, ssaoDepthTextureID);

glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT24, 1024, 1024, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE);

glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, ssaoDepthTextureID, 0);

glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);

glBindFramebuffer(GL_FRAMEBUFFER, 0);

And the depth pass code I call each frame before regular draw:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glBindTexture(GL_TEXTURE_2D, 0);
glBindFramebuffer(GL_FRAMEBUFFER, ssaoFramebufferID);
glViewport(0, 0, 1024, 1024);

depthShader.Bind();
depthShader.SetUniformMatrixfv("depthMVP", camera.GetViewMatrix() * Matrix4::Perspective(60, aspectRatio, 0.1f, 10.0f));

DrawScene(true);

glBindFramebuffer(GL_FRAMEBUFFER, 0);
glViewport(0, 0, width, height);

My depth shaders, vertex:

#version 330 core

layout(location = 0) in vec3 Position;

uniform mat4 depthMVP;

void main() {
    gl_Position = depthMVP * vec4(Position, 1.0);
}

fragment:

#version 330 core

layout(location = 0) out float fragmentdepth;

void main() {
    fragmentdepth = gl_FragCoord.z;
}

EDIT2: The glClear call where it currently is gives me a completely black texture. Putting it below the first glViewport call gives the depth image I displayed above though:

glBindTexture(GL_TEXTURE_2D, 0);
glBindFramebuffer(GL_FRAMEBUFFER, ssaoFramebufferID);
glViewport(0, 0, 1024, 1024);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

Answer 1

I managed to get it working thanks to some help in the comments:

My code is now as follows, fragment shader:

#version 330 core

in vec2 TexCoord0;

smooth in vec3 vNormal;
smooth in vec3 vWorldPos;
in mat4 ProjectionMatrix;

uniform sampler2D uDepthTex;
uniform float uWidth;
uniform float uHeight;

layout(location = 0) out vec4 FragColor;

void main()
{
    vec2 res = gl_FragCoord.xy / vec2(uWidth, uHeight);
    FragColor = texture(uDepthTex, res);
}

Framebuffer creation:

glGenFramebuffers(1, &ssaoFramebufferID);
glBindFramebuffer(GL_FRAMEBUFFER, ssaoFramebufferID);

glGenTextures(1, &ssaoDepthTextureID);
glBindTexture(GL_TEXTURE_2D, ssaoDepthTextureID);

glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, 1024, 768, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE);

Depth draw code:

glBindFramebuffer(GL_FRAMEBUFFER, ssaoFramebufferID);
glViewport(0, 0, 1024, 768);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

depthShader.Bind();

glDisable(GL_ALPHA_TEST);

depthShader.SetUniformMatrixfv("depthMVP", Matrix4::Perspective(60, aspectRatio, 0.1f, 10.0f) * camera.GetViewMatrix());

DrawScene();

glBindFramebuffer(GL_FRAMEBUFFER, 0);
glViewport(0, 0, width, height);
glEnable(GL_ALPHA_TEST);