NickName:benitosub Ask DateTime:2011-09-12T20:48:50

iPhone Dev: Render Depth Buffer to Texture results in black texture

EDIT: I took FBOs out of the equation to make sure the problem wasn't coming from there, so now I am just doing the following:

setup texture:

GLuint FB0Texture;
glGenTextures(1, &FB0Texture);
glBindTexture(GL_TEXTURE_2D, FB0Texture);
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_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_COMPONENT16, size.width, size.height, 
                 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, 0);

and then to render:

[self drawScene];

[(EAGLView *)self.view bindFB0];

glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, 320, 480);

[self drawFullScreenQuad]; (it's actually not full screen so I can see both the 3d scene and the resulting texture)

and I get the same results! Black texture if I setup FB0Texture as a "DEPTH_COMPONENT" texture, but normal scene if I setup FB0Texture as a regular GL_RGBA texture...

So I guess I am either setting up the depth texture wrong, or is it possible I am doing something wrong in the rendering which would result in the RGBA texture looking normal but the depth texture being screwed? GL_DEPTH_TEST is enabled and working fine (models look correct) so I think there is nothing wrong with the actual rendering, but at this point I am desperate for clues ...

Please help!

// END OF EDIT

I am trying to implement some basic shadow mapping on iphone, but I am stuck at rendering the depth values to a texture ... This is driving me crazy, I am obviously doing something wrong but cannot figure out what it is ...

So what I am doing :

setup default framebuffer, attach color render buffer and depth render buffer
setup a new framebuffer (call it FB0), attach a texture to the depth component

Then when I render:

draw scene to FB0
switch to default framebuffer
draw full screen quad using FB0 as a texture

And I get ... nothing! (well I get a full white texture)

If I attach the texture to the color component of FB0 instead of the depth component, everything works fine, as in I draw the scene to FB0, then use FB0 as a texture to draw a full screen quad, and I see exactly what I would see if I was drawing directly to the default framebuffer.

However when I attach the texture to the depth component, all I get is this white screen / texture.

Some code:

setup buffers:

// Create default framebuffer object.
glGenFramebuffers(1, &defaultFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);

// Create color render buffer and allocate backing store.
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);

// Create depth render buffer
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, 320, 480); 
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);


// Create Depth Map Frame Buffer

glGenFramebuffers(1, &FB0);
glBindFramebuffer(GL_FRAMEBUFFER, FB0);

// Attach texture to depth component        

glGenTextures(1, &FB0Texture);
glBindTexture(GL_TEXTURE_2D, FB0Texture);
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_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_COMPONENT, size.width, size.height, 
                 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT, 0);

glFramebufferTexture2D(GL_FRAMEBUFFER, 
                       GL_DEPTH_ATTACHMENT, 
                       GL_TEXTURE_2D, 
                       FB0Texture, 
                       0);

If I check the status of the framebuffers after this I get no error messages, so I am assuming the buffers are created correctly.

Then in the rendering:

[(EAGLView *)self.view setFB0]; (just binds the framebuffer)

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

[self drawScene];

[(EAGLView *)self.view setFramebuffer]; (binds back the default frame buffer)

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

[(EAGLView *)self.view bindFB0Texture];

[self drawFullScreenQuad];

[(EAGLView *)self.view presentFramebuffer];

At this point I would expect to see a black and white texture with levels of gray indicating the depth, but instead I just get a solid white quad / texture.

Again, if I attach FB0Texture to GL_COLOR_ATTACHMENT0 instead of GL_DEPTH_ATTACHMENT everything works as expected, my scene gets rendered to the texture correctly. So I guess the problem is coming from how I am attaching the texture, or maybe the order in which I am doing stuff ?

Copyright Notice：Content Author:「benitosub」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/7388128/iphone-dev-render-depth-buffer-to-texture-results-in-black-texture