OpenGL depth buffer to texture (for various image sizes) - opengl

I'm having a problem with the depth buffer. I want to put into a texture. But it doesn't seem to work.
So, here's the piece of code I execute after rendering the objects:
glGenTextures(1, (GLuint*)&_depthTexture);
glBindTexture(GL_TEXTURE_2D, _depthTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
const pair<int, int> &img_size = getImageSize();
glTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32, img_size.first, img_size.second, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, img_size.first, img_size.second);
glClear( GL_DEPTH_BUFFER_BIT );
The thing is (I'm with OpenGL 3.2+), the image for rendering has different size. Most of the time, it won't be a 2^i by 2^j for the size. So, is that a problem ?
Also, the other part of the problem might be in the fragment shader after:
#version 140
uniform sampler2D depthTexture;
uniform ivec2 screenSize;
out vec4 outColor;
void main()
{
vec2 depthCoord = gl_FragCoord.xy / screenSize.xy;
float d = texture2D(depthTexture, depthCoord).x;
outColor = vec4(d, d, d, 1.0);
}
After that, when I render a second time some shapes, I want to use the previous depth (the texture depth buffer), to do some effects.
But seriously... can anyone just show me a piece of code where you can get the depth buffer into a texture? I don't care if it's rendering to the texture or if the texture is extracted after the rendering! As long as I have a texture with the depth value to do the second pass... that's what is important!

http://www.joeforte.net/projects/soft-particles/
this might be a good solution!
At least, it's the full code... might be able to get all the different parts!

You may need a glReadBuffer call. If your context is double-buffered, that would be glReadBuffer( GL_BACK ).
Also, try GL_DEPTH_COMPONENT24, since a 32-bit depth buffer would be unusual, I think.

Related

Calculating color histogram of framebuffer inside compute shader

As the title suggests, I am rendering a scene onto a framebuffer and I am trying to extract the color histogram from that framebuffer inside a compute shader. I am totally new to using compute shaders and the lack of tutorials/examples/keywords has overwhelmed me.
In particular, I am struggling to properly set up the input and output images of the compute shader. Here's what I have:
computeShaderProgram = loadComputeShader("test.computeshader");
int bin_size = 1;
int num_bins = 256 / bin_size;
tex_w = 1024;
tex_h = 768;
GLuint renderFBO, renderTexture;
GLuint tex_output;
//defining output image that will contain the histogram
glGenTextures(1, &tex_output);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex_output);
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_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R16, num_bins, 3, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, NULL);
glBindImageTexture(0, tex_output, 0, GL_FALSE, 0, GL_WRITE_ONLY, GL_R16UI);
//defining the framebuffer the scene will be rendered on
glGenFramebuffers(1, &renderFBO);
glGenTextures(1, &renderTexture);
glBindTexture(GL_TEXTURE_2D, renderTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, W_WIDTH, W_HEIGHT, 0, GL_RGBA, GL_FLOAT, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glBindFramebuffer(GL_FRAMEBUFFER, renderFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, renderTexture, 0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
In the main loop I draw a simple square onto the framebuffer and attempt to pass the framebuffer as input image to the compute shader:
glBindFramebuffer(GL_FRAMEBUFFER, renderFBO);
glDrawArrays(GL_TRIANGLES, 0, 6);
glUseProgram(computeShaderProgram);
//use as input the drawn framebuffer
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, renderFBO);
//use as output a pre-defined texture image
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, tex_output);
//run compute shader
glDispatchCompute((GLuint)tex_w, (GLuint)tex_h, 1);
GLuint *outBuffer = new GLuint[num_bins * 3];
glGetTexImage(GL_TEXTURE_2D, 0, GL_R16, GL_UNSIGNED_INT, outBuffer);
Finally, inside the compute shader I have:
#version 450
layout(local_size_x = 1, local_size_y = 1) in;
layout(rgba32f, binding = 0) uniform readonly image2D img_input;
layout(r16ui, binding = 1) uniform writeonly image2D img_output;
void main() {
// grabbing pixel value from input image
vec4 pixel_color = imageLoad(img_input, ivec2(gl_GlobalInvocationID.xy));
vec3 rgb = round(pixel_color.rgb * 255);
ivec2 r = ivec2(rgb.r, 0);
ivec2 g = ivec2(rgb.g, 1);
ivec2 b = ivec2(rgb.b, 2);
imageAtomicAdd(img_output, r, 1);
imageAtomicAdd(img_output, g, 1);
imageAtomicAdd(img_output, b, 1);
}
I defined the output as a 2d texture image of size N x 3 where N is the number of bins and the 3 accounts for the individual color components. Inside the shader I grab a pixel value from the input image, scale it into the 0-255 range and increment the appropriate location in the histogram.
I cannot verify that this works as intended because the compute shader produces compilation errors, namely:
can't apply layout(r16ui) to image type "image2D"
unable to find compatible overloaded function "imageAtomicAdd(struct image2D1x16_bindless, ivec2, int)"
EDIT: after changing to r32ui the previous error now becomes: qualified actual parameter #1 cannot be converted to less qualified parameter ("im")
How can I properly configure my compute shader?
Is my process correct (at least in theory) and if not, why?
As for your questions:
can't apply layout(r16ui) to image type "image2D"
r16ui can only be applied to unsigned image types, thus you should use uimage2D.
unable to find compatible overloaded function ...
The spec explicitly says that atomic operations can only by applied to 32-bit types (r32i, r32ui, or r32f). Thus you must use a 32-bit texture instead.
Your have other issues in your code too.
glBindTexture(GL_TEXTURE_2D, renderFBO);
You cannot bind an FBO to a texture. You should instead bind the texture that backs the FBO (renderTexture).
Also, you intend to bind a texture to an image uniform rather than a sampler, thus you must use glBindImageTexture or glBindImageTextures rather than glBindTexture. With the later you can bind both images in one call:
GLuint images[] = { renderTexture, tex_output };
glBindImageTextures(0, 2, images);
Your img_output uniform is marked as writeonly. However the atomic image functions expect an unqualified uniform. So remove the writeonly.
You can find all the above information in the OpenGL and GLSL specs, freely accessible from the OpenGL registry.

Rendering a framebuffer to texture wont work

I am trying to create a depth map in OpenGL and for some reason the framebuffer wont write to the texture, I tried multiple things to fix it but it doesn't seem to work.
Here is what I did:
This is the generation of the framebuffer and the texture:
glGenFramebuffers(1, &_DepthMapFBO);
glBindFramebuffer(GL_FRAMEBUFFER, _DepthMapFBO);
glGenTextures(1, &_DepthMapTex);
glBindTexture(GL_TEXTURE_2D, _DepthMapTex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, DEPTH_TEXTURE_WIDTH, DEPTH_TEXTURE_HEIGHT, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
//glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, _DepthMapTex, 0);
glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, _DepthMapTex, 0);
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
(In the above I tried replacing glTexImage2D with glTexStorage2D and I tried replace glFramebufferTexture with glFramebufferTexture2D, both didn't work)
Then (There is stuff before this but they work find, I checked) I rendered the framebuffer as follows:
_DepthProgram.Use();
// Setting uniforms here
glViewport(0, 0, DEPTH_TEXTURE_WIDTH, DEPTH_TEXTURE_HEIGHT);
glBindFramebuffer(GL_FRAMEBUFFER, _DepthMapFBO);
glClear(GL_DEPTH_BUFFER_BIT);
// Rendering the scene here
glBindFramebuffer(GL_FRAMEBUFFER, 0);
These are the shaders I use:
(Vertex)
#version 410 core
layout(location = 0) in vec3 Position;
uniform mat4 LightSpaceMatrix;
uniform mat4 Model;
void main()
{
gl_Position = LightSpaceMatrix * Model * vec4(Position, 1.0);
}
(Fragment)
#version 410 core
void main()
{
// gl_FragDepth = 0.0;
}
I tried rendering the texture to a plane and it came out totally white (I Checked there was supposed to be other values), As you can see in the fragment shader, I tried to explicitly write to the gl_FragDepth but it didn't change the texture, it kept it white (1.0).
I looked all over the internet and looked at learnopengl.com and everybody seem to be doing the same as me, did I miss something?
(I double checked and I am rendering the texture to the plane right, I replaced the glBindTexture with another one and it rendered the texture)
If I am missing some information please let me know.
EDIT: By the way, I don't get any error with glGetError.

Opengl glsl can't mix 2d textures and 3d textures

[Edit2]: Nothing wrong with this code. My shader class didn't load the uniforms correctly.
[Edit]: It seems like I can only use GL_TEXTURE0/texture unit 0 by some reason.
What I want is to draw a 2d texture and a 3d texture, but only the texture with texture unit 0(GL_TEXTURE_0) will work. And I use both of them at the same time in the shader I can't see anything using that shader.
This is the fragment shader code I want to use:
#version 330 core
// Interpolated values from the vertex shaders
in vec3 fragmentColor;
in vec3 fragmentPosition;
// Ouput data
out vec3 color;
uniform sampler3D textureSampler3D;
uniform sampler2D textureSampler2D;
float getInputLight(vec3 pos);
void main(){
// Get the nearest corner
vec3 cornerPosition = vec3(round(fragmentPosition.x), round(fragmentPosition.y), round(fragmentPosition.z));
float light = getInputLight(cornerPosition);
color = (0.5+16*light)*fragmentColor;
}
float getInputLight(vec3 pos) {
if (pos.z <= 0.f)
return texture2D(textureSampler2D, vec2(pos.x/16, pos.y/16)).r;
return texture(textureSampler3D, vec3(pos.x/16, pos.y/16, pos.z/16)).r;
}
But with that I can't see anything made by that shader. If I use this I can see what the 2d textures does.
float getInputLight(vec3 pos) {
if (pos.z <= 0.f)
return texture(textureSampler2D, vec2(pos.x/16, pos.y/16)).r;
return 0.f;
}
If I use this it will work perfectly except that I only have the 3d texture:
float getInputLight(vec3 pos) {
return texture(textureSampler3D, pos/16).r;
}
That means that I can only use one of the textures on the shaders. When I say that I use the 3d texture then I change getInputLight so I it just used the 3d texture. I do the same thing with 2d textures except that I change it to the other version.
This is the c++ code I use to load the 3d texture:
glGenTextures(1, &m_3dTextureBuffer);
glBindTexture(GL_TEXTURE_3D, m_3dTextureBuffer);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage3D(GL_TEXTURE_3D, 0, GL_R8, voxelMatrixWidth, voxelMatrixHeight, voxelMatrixDepth, 0, GL_RED, GL_UNSIGNED_BYTE, (GLvoid*)m_lightData);
This is the code I use to load the 2d texture:
GLuint buffer;
unsigned char *voidData = new unsigned char[256];
// With this I can see if the shader has right data.
for (int i = 0; i < 256; ++i)
voidData[i] = i%16;
glGenTextures(1, &buffer);
glBindTexture(GL_TEXTURE_2D, buffer);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, 16, 16, 0, GL_RED, GL_UNSIGNED_BYTE, (GLvoid*)voidData);
m_3dTextureBuffer = buffer;
This is the code I run before it draws the vertex buffer:
GLint texture3dId = shader->getUniform(1);
GLint texture2dId = shader->getUniform(2);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_3D, m_3dTextureBuffer);
glUniform1i(texture3dId, 0);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, m_2dTextureBuffer);
//glUniform1i(texture3dId,1);
If I use texture unit 0(TEXTURE0) for both 2d texture and 3d texture I get data/pixels of what I expect.
This is a picture of it and it is what I expect:
http://oi57.tinypic.com/3wrbd.jpg
If I use different units I get this random data and it falshes sometimes(every pixel turns black/0 for a frame). The random data doesn't change either. If you look in some direction it doesn't flash and some directions flash faster than others.
http://oi58.tinypic.com/2ltiqoo.jpg
When I swap texture unit of the 3d texture an the 2d texture the same thing happens, but the 2d texture works an the 3d texture fails.
Do you have any idea what it could be?
There was nothing wrong with this code. My shader class didn't load the uniforms correctly.

OpenGL 3.30 / GLSL 3.30 - MRT outputting black textures

I've been stuck with this problem for about four days now. I'm trying to get my geometry to rendered into an FBO (G-buffer) with three textures (albedo, normal, depth). So far, I've 'somewhat' implemented MRT functionality, but when I use gDEBugger to inspect the textures, they just appear black. No matter what I change, they result in solid black. The actual values outputted are correct, I checked by disabling MRT to make the fragment shader output to back buffer. The textures are being initialized properly, gDEBugger properly displays the parameters I have put for them. But they all just have a solid black (0, 0, 0, 255) fill.
There's hardly any elaborate information on MRTs for GLSL 3.30. I've relied entirely on answered questions here, along with the OpenGL/GLSL docs and tutorials across the web (outdated, but I updated the code). I've probably spent a full day looking for a solution for this problem on Google. If there's something wrong with the ordering of the code, or syntax, please point it out. I don't even know if this implementation is correct anymore...
I'm using Visual C++ 2010, OpenGL 3.30 and GLSL 3.30 (as said in the title). For my libraries, GLFW 3.0 is being used for the windows, input, and OpenGL context, and GLEW 1.10.0 for extensions.
Keep in mind that all of this code is taken from my wrapper class. The ordering of the code is how it is all run at runtime (in other words, it's like as if I didn't have a wrapper class, and all of the code was in main ()).
Initialization Stage
// Initialize textures
glGenTextures (3, tex_ids);
glEnable (GL_TEXTURE_2D);
glBindTexture (GL_TEXTURE_2D, tex_ids[0]); // Diffuse
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);
glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB8, res.x, res.y, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glBindTexture (GL_TEXTURE_2D, tex_ids[1]); // Normal
glTexParameterf (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf (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);
glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB8, res.x, res.y, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glBindTexture (GL_TEXTURE_2D, tex_ids[2]); // Depth
glTexParameterf (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf (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);
glTexImage2D (GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32, res.x, res.y, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
glBindTexture (GL_TEXTURE_2D, 0);
glDisable (GL_TEXTURE_2D);
// Initialize FBO
glEnable (GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tex_ids[0]);
glFramebufferTexture2D ( GL_FRAMEBUFFER,
GL_COLOR_ATTACHMENT0,
GL_TEXTURE_2D,
tex_ids[0],
0 ); // diffuse
glBindTexture(GL_TEXTURE_2D, tex_ids[1]);
glFramebufferTexture2D ( GL_FRAMEBUFFER,
GL_COLOR_ATTACHMENT1,
GL_TEXTURE_2D,
tex_ids[1],
0 ); // normal
glBindTexture(GL_TEXTURE_2D, tex_ids[2]);
glFramebufferTexture2D ( GL_FRAMEBUFFER,
GL_DEPTH_ATTACHMENT,
GL_TEXTURE_2D,
tex_ids[2], 0 ); // depth
glBindFramebuffer (GL_FRAMEBUFFER, 0);
glDisable (GL_TEXTURE_2D);
// Initialize shaders
// Snipped out irrelevant code relating to getting shader source & compiling shaders
glBindFragDataLocation (renderer_1prog, GL_COLOR_ATTACHMENT0, "diffuse_out");
glBindFragDataLocation (renderer_1prog, GL_COLOR_ATTACHMENT1, "normal_out");
glBindFragDataLocation (renderer_1prog, GL_DEPTH_ATTACHMENT, "depth_out");
// More snipped out code relating to linking programs and finalizing
Draw Stage - called on every frame
// Bind everything
glUseProgram (renderer_1prog);
glBindFramebuffer (GL_DRAW_FRAMEBUFFER, fbo_id);
GLenum targ [3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_DEPTH_ATTACHMENT };
glDrawBuffers (3, targ);
// Draw mesh
glEnable (GL_CULL_FACE);
glEnable (GL_DEPTH_TEST);
teshmesh.draw ();
// Unbind fbo
glDisable (GL_CULL_FACE);
glDisable (GL_DEPTH_TEST);
glBindFramebuffer (GL_READ_FRAMEBUFFER, 0);
glBindFramebuffer (GL_DRAW_FRAMEBUFFER, 0);
Vertex Shader
#version 330
layout(location = 0)in vec4 v;
layout(location = 1)in vec3 c;
layout(location = 2)in vec3 n;
out vec4 pos;
out vec3 col;
out vec3 nrm;
uniform mat4 projection;
uniform mat4 view;
uniform mat4 world;
void main () {
gl_Position = projection * view * world * v;
pos = view * world * v;
pos.z = -pos.z / 500.0;
col = c.xyz;
nrm = n;
}
Fragment Shader
#version 330
in vec3 col;
in vec3 nrm;
in vec4 pos;
layout(location = 0) out vec3 diffuse_out;
layout(location = 1) out vec3 normal_out;
layout(location = 2) out vec3 depth_out;
out vec3 o;
void main () {
diffuse_out = col;
normal_out = (nrm / 2.0) + 0.5;
depth_out = vec3 (pos.z, pos.z, pos.z);
}
There are a few problems here. Starting with the smallest:
glBindFragDataLocation (renderer_1prog, GL_COLOR_ATTACHMENT0, "diffuse_out");
glBindFragDataLocation (renderer_1prog, GL_COLOR_ATTACHMENT1, "normal_out");
glBindFragDataLocation (renderer_1prog, GL_DEPTH_ATTACHMENT, "depth_out");
These are pointless. You used layout(location) syntax in your shader to specify this, and that takes priority over OpenGL-provided location settings.
Also, these are wrong. You don't put the FBO buffer attachment name into the location; you put an index into the location. So even if you didn't use layout(location), this is simply incorrect. glBindFragDataLocation will emit an OpenGL error, since the location will most assuredly be larger than GL_MAX_DRAW_BUFFERS​.
Considering how many OpenGL errors your code should emit, I'm rather surprised that your use of gDEBugger didn't tell you about any of these.
glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB8, res.x, res.y, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
GL_RGB8 is not one of the required image formats for render targets. Therefore, the implementation is not required to support it; it may but it doesn't have to. And since you never bothered to check the completeness of the FBO (FYI: you should always do that), you didn't test that this combination of formats is valid.
Never render to a 3-component image. Pick 4, 2, or 1 instead.
GLenum targ [3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_DEPTH_ATTACHMENT };
glDrawBuffers (3, targ);
This is probably your main problem: your glDrawBuffers call fails. glDrawBuffers sets the color buffer outputs. The depth buffer is not a color buffer. There's only one depth buffer, so there's no need to set it.
To write to the depth buffer... well, you shouldn't be writing a user-calculated value to the depth buffer. Just let the regular depth buffer writing handle it. But if you want to (and let me remind you again, you do not), you write to gl_FragDepth. That's what it's for.

Write depth buffer from Cg and then read it from OpenGL

I'd like to create a shadow map with cg. I have written an opengl program and 2 pixel shaders (with 2 vertex shader). In the first pixel shader, I write the DEPTH register, and in the OpenGL program I read this to a texture. In the second pixel shader I'd like to read from this texture, however it seems to contain only 0 values. There is another texture in both shaders, I don't know if that van be a problem, but I don't think so.
The first shader is like this:
void main( in float3 point : TEXCOORD0,
out float3 color : COLOR,
out float depth : DEPTH)
{
// here I calculate the distances (c)
color = float3(c, c, c);
depth = c;
}
In the OpenGL program I created a texture for the depth component:
glGenTextures(1, &shadowtex_id);
glBindTexture(GL_TEXTURE_2D, shadowtex_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, RES, RES, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
Enabled the GL_DEPTH_TEST, then after displaying the objects:
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, RES, RES);
then in the second shader:
float depth = tex2D(shadow_array, depthcoord);
// depthcoord is the actual point's coordinate's in the light's coordinate system
// epsilon is a very small number
if (this_depth < depth + epsilon) {
color = float3(depth, depth, depth);
}
And all I'm getting is an all black screen. I tried various things, and I've come to that conclusion, that it seems like my
uniform sample2D shadow_array
is containing only 0 values. Because if I change depth's value for example to 0.2, then it's working, so I think the problem is either with the reading from the z-buffer, or reading the shadow map's texture. So how can I save the z-buffer's content to a texture in opengl?