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OpenGL FBO Sampling/Filtering Artifacts

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Hey out there ! I'm pretty new around here, so I apologize in advance for any stupid question, that may have been answered elsewhere. I just googled for a while and couldnt find anything though. I recently got to work with FBOs in OpenGL and use them now as RTT facility for combining various postprocess effects. I like their window independed resolution, unfortunately this seems to be the point I am struggling with now, as I am running into strange blocky artifacts when I render the texture onscreen (by using a quad). It looks a little like moiree mixed with dithering (see image link). The test scene the image is rendered at 800x600 while the texture containing the shadow areas (rendered in a previous pass) is rendered at 256x256. Filtering artifacts[25kb] Increasing the resolution of the texture doesnt help, so I can only guess that its the mapping from a square to the 1.8 ratio I am using for my output. Someone mentioned that filtering of the framebuffers is not specified in the spec and thus driver specific. Has anybody seen anything comparable ? I am using my notebooks ATI mobility 9700 (with Omega Drivers) for the testing right now, couldn't manage to get a hand on a NVIDIA card yet. Any help appreciated, thanks in advance :) Christian

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Just to close this topic :

Tested it on a ATI Radeon 9700 (no mobility this time) and the artifacts are gone.
Seems like a driver issue of the omega drivers *shrugging my shoulders*

Thnx anyway :)

Christian

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rendering a 256x256 sized texture on a polygon of 800x600 is gonna aways look blurry and will be slightly stretched (distorted) use only 256x192 of the 256x256 texture (u will need to change texture coords) or use NPOT etc

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Thanks for the reply ! Blurring/stretching wasn't an issue though, it just seems that the driver couldnt properly blit to the attached texture, so pixels showed up in repetitive patterns at wrong places. *still rather clueless about it*

Thanks anyway :)

Christian

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