I am rendering a scene to FBO as my render target whose size is 8 times the size of the orignal screen in OpenGL. Now i wan to downsample the texture generated by FBO to the size of the screen so as to achieve spatial anti aliasing. How do i achieve the down sampling ? Please provide implementation details.
Note : If there is a better way of doing anti aliasing in FBOs please mention that too. I am trying to remove the aliasing in the image attached below.

enter image description here

  • 2
    \$\begingroup\$ I feel sorry for your GPU \$\endgroup\$ Commented Nov 16, 2011 at 2:34
  • \$\begingroup\$ How are you drawing the grid? \$\endgroup\$ Commented Nov 16, 2011 at 8:27
  • \$\begingroup\$ @NicolBolas a texture for 1X1 sqaure block and then I am mapping it all over the grid. \$\endgroup\$
    – snape
    Commented Nov 16, 2011 at 8:34

1 Answer 1


Since your render target is exactly 8 times the size of the screen, I'd just use glGenerateMipmap, after setting glTexParameteri(..., GL_TEXTURE_MAX_LEVEL, 3);. Then, just blit or whatever from mipmap level 3, and you're done.

But really, you're wasting a lot of performance by not using multisampling+aniso. Supersampling won't give you much that you won't get with multisampling and anisotropic filtering, and your rendering will be that much faster for it.

  • \$\begingroup\$ You could also replace blitting with simply drawing a textured sprite that covers the screen area exactly, that also works for non power of 2 scaling. \$\endgroup\$ Commented Nov 16, 2011 at 11:14

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