Simplified version of my deferred rendering looks like this:

  • bind fbo1
  • clear color and depth buffers
  • gbuffer stage (gbuffer contains only these pixels which pass a depth test)
  • unbind fbo1

  • bind fbo2

  • clear color buffer
  • draw a full screen quad, shading stage (render to the texture for some post processing effects)
  • unbind fbo2

  • clear color and depth buffers

  • draw a full screen quad and render to the default framebuffer

How to combine that with the forward rendering ?


1 Answer 1


Copy the depth information to the la-buffer and then render normally to the la-buffer using forward shading. All you need to do to copy over the depth information is add this to the light accumulation fragment shader:

gl_FragDepth = texture(depthBuffer, texCoord).r;
  • \$\begingroup\$ The gbuffer(fbo1) contains a depth texture and a depth attachment. When fbo1 is bound I set glDrawBuffers and I use a gbuffer shader. So after that (when fbo1 is still bound) I should switch a shader program and use a forward rendering !? \$\endgroup\$
    – Irbis
    Feb 4, 2013 at 18:18
  • \$\begingroup\$ No, you need to render to the la-buffer or the default framebuffer. You need to make sure that the la-buffer has a depth attachment. \$\endgroup\$
    – jmegaffin
    Feb 4, 2013 at 18:23
  • \$\begingroup\$ Ok, now the la-buffer has a depth attachment. I render (forward rendering) to the default framebuffer at the end (after a full screen quad) but the result of the forward rendering is behind a full screen quad. I checked that using glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); How the depth data is moved from fbo1 to fbo2 ? Maybe here something is wrong. \$\endgroup\$
    – Irbis
    Feb 4, 2013 at 22:35
  • \$\begingroup\$ In the light accumulation shader, read in the depth value from the g-buffer and output it to the la-buffer using gl_FragDepth. \$\endgroup\$
    – jmegaffin
    Feb 5, 2013 at 0:39
  • \$\begingroup\$ You shouldn't need to copy the depth value anywhere. Just attach the same depth buffer to both FBOs. \$\endgroup\$ Feb 5, 2013 at 1:06

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