CODEWITHSUNDEEP
openglglslgpgpu
Frederik Slijkerman
Frederik Slijkerman

Reputation: 6529

How to cancel a blocking OpenGL call

I'm investigating GPGPU programming with OpenGL + GLSL. One problem is that if you have a shader that takes a long time to finish, it seems to be impossible to cancel it.

After setting up everything, I issue the final glReadPixels call which blocks until all pixels have been rendered to a framebuffer. Depending on the shader, this could take a long time, even seconds. Is there a way to cancel the call (from another thread) or even query the progress? What happens if you set up an infinite loop in a shader?

Upvotes: 0

Views: 679

Answers (2)

Unick
Unick

Reputation: 674

What happens if you set up an infinite loop in a shader?

I think you will get crash of video driver.

Upvotes: 0

fen
fen

Reputation: 10115

instead of glReadPixels you could use PixelBufferObjects which are not blocking. glReadPixels will wait (in your main thread) for the results, but PBO will continue... somewhere later in the code you can check if the data in PBO are available.

http://www.songho.ca/opengl/gl_pbo.html

http://www.opengl.org/wiki/Pixel_Buffer_Object

if you need some more advanced calculations then you may want to use OpenCL, that will give you more flexibility.

Upvotes: 3

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