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Cyraxx

OpenGL Multiple Passes

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Cyraxx    122
Hey. When I create vertex and fragment shaders in ATI's RenderMonkey I have the option to render a pass to a texture and thereby having multiple passes in my shader. How do I do the same thing with my OpenGL code, that is I need to render one pass to a texture and then use this texture in a second pass etc. ?

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JavaCoolDude    670
1-set your view port to the dimensions of your texture
2-render your stuff normally
3-bind the texture where you want the result to be rendererd and use glCopyTexSubImage2D
4-Tada :D
Well there are other alternatives such as the use of FBOs and Pixel buffers, let me know if you would like to know more about them :)

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Cyraxx    122
Thanks for the reply.

This seems to work, but is there a way to dump the Z-buffer to texture as well? I'm trying to do some tranparency stuff and it would be helpful to have access to the Z-buffer?

Maybe FBOs and Pixel buffers are the answer? :) (I have no idea what those are.)

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stroma    218
"glReadPixels" function easy to use to get depth value, but it is really slow. some more function can be used for this but i recommend you to get the values from fragment shader. gl_color.z is the z-buffer value for that pixel.

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Optus    422
I thought you could do it with glCopyTexSubImage2D, but it appears you cannot. You will want to use glCopyTexImage2D (Does the same thing, someone tell me why you would want to use glCopyTexSubImage2D instead, please). This may be slower, then SubImage, but i'm not sure. This function takes a parameter "internal format" that you can set to GL_DEPTH_COMPONENT, to copy the z buffer.

SIDE NOTE: JCD, How'd it go with nvidia???

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