OpenGL, how to use depthbuffer from framebuffer as usual depth buffer

opengl framebuffer depth-buffer
ShPavel picture ShPavel · Mar 28, 2012 · Viewed 8k times · Source

I have frame buffer, with depth component and 4 color attachments with 4 textures

I draw some stuff into it and unbind the buffer after, using 4 textures for fragment shader (deferred lighting). Later i want to draw some more stuff on the screen, using the depth buffer from my framebuffer, is it possible?

I tried binding the framebuffer again and specifying glDrawBuffer(GL_FRONT), but it does not work.

Answer

Christian Rau picture Christian Rau · Mar 28, 2012

Like Nicol already said, you cannot use an FBOs depth buffer as the default framebuffer's depth buffer directly.

But you can copy the FBO's depth buffer over to the default framebuffer using the EXT_framebuffer_blit extension (which should be core since GL 3):

glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, 
                  GL_DEPTH_BUFFER_BIT, GL_NEAREST);

If this extension is not supported (which I doubt when you already have FBOs), you can use a depth texture for the FBO's depth attachment and render this to the default framebuffer using a textured quad and a simple pass through fragment shader that writes into gl_FragDepth. Though this might be slower than just blitting it over.

Related questions

Render depth from framebuffer texture

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 …

Read More
What's the concept of and differences between Framebuffer and Renderbuffer in OpenGL?

I'm confused about concept of Framebuffer and Renderbuffer. I know that they're required to render, but I want to understand them before use. I know some bitmap buffer is required to store the temporary drawing result. The back buffer. And …

Read More
OpenGL: Trouble with Render to Texture & Framebuffer Object

I'd like to render a scene to an initially empty texture. To do so, I use a Framebuffer Object to which I attach an empty 2d texture and a depth buffer. After the set up, as for testing, I draw …

Read More