# glReadPixels() generating artifacts

**URL:** <https://forums.imgtec.com/t/glreadpixels-generating-artifacts/1500>\
**Category:** PowerVR Insider\
**Created:** [August 16, 2012, 7:00pm UTC](https://forums.imgtec.com/t/glreadpixels-generating-artifacts/1500 "2012-08-16T19:00:57Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![iceman](https://avatars.discourse-cdn.com/v4/letter/i/46a35a/32.png) [@iceman](https://forums.imgtec.com/u/iceman)\
**Post date:** [August 16, 2012, 7:00pm UTC](https://forums.imgtec.com/t/glreadpixels-generating-artifacts/1500/1 "2012-08-16T19:00:57Z")

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I have noticed that with the SGX545 driver, glReadPixels() reads the framebuffer prior to it has been rendered to, at sufficiently small viewports. Is this a known driver bug?

  

Thanks.

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**Author:** ![JoeDavis](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/joedavis/32/71_2.png) [@JoeDavis](https://forums.imgtec.com/u/JoeDavis)\
**Post date:** [September 5, 2012, 7:43am UTC](https://forums.imgtec.com/t/glreadpixels-generating-artifacts/1500/2 "2012-09-05T07:43:16Z")

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Hi iceman,  
  
Can you share an image that highlights this problem?  
  
a glReadPixels() will force the GPU to kick a render. Once the render is complete, the GPU will stall until the CPU has finished its call to glReadPixels() (i.e. the data has been retrieved).  
  
Thanks,  
Joe