I'm getting some artifacts when I try to use a colour attachment on an FBO. I'm saving my first pass as a texture, then passing it as an input to an anti-aliasing shader. The result is, as below, some weird noise and an enforced black background. The AA is applied fine.


GL.BindFramebuffer(FramebufferTarget.FramebufferExt, _hndFBO);
GL.BindTexture(TextureTarget.Texture2D, 0);
GL.DrawBuffer((DrawBufferMode) FramebufferAttachment.ColorAttachment0Ext);
GL.Viewport(0, 0, _intWidth, _intHeight);
//Do rendering here
GL.BindFramebuffer(FramebufferTarget.FramebufferExt, 0);

Any ideas? Need more code?


1 Answer 1


Are you clearing the back buffer before you render to it each frame?

I'm assuming magenta is "transparent" in the first picture. If so, the parts of the back-buffer where there is no terrain are not affected. Residual data could very well account for what you are seeing.

  • \$\begingroup\$ PS: the anti-aliased terrain looks lovely! \$\endgroup\$
    – drxzcl
    Aug 15, 2010 at 11:18
  • \$\begingroup\$ Yeah, that looks like a classic "didn't clear the buffer" issue. \$\endgroup\$
    – JasonD
    Aug 15, 2010 at 11:58
  • \$\begingroup\$ Fixed it! I was clearing the buffer too early it seems. I had figured that was the issue initially but after trying a few combinations it wasn't helping and I, mistakenly, moved on. @Ranieri Thanks :) I've got a version with a higher LOD: facebook.com/… Still plenty of work to go... \$\endgroup\$
    – Rushyo
    Aug 15, 2010 at 12:35
  • \$\begingroup\$ (Only started playing with OpenGL this week) \$\endgroup\$
    – Rushyo
    Aug 15, 2010 at 12:36
  • \$\begingroup\$ Hmmm.. spoke too soon. That killed the AA... Ah well. I'll have a poke around. Least I'm sure of where to look now. Thanks! \$\endgroup\$
    – Rushyo
    Aug 15, 2010 at 12:40

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