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Rendering to texture - without clearing scene

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Hi, I'm trying to render a small amount of quads to a texture, without rendering the whole scene to the same texture. BUT - only way I've found to achieve this, is to follow this procedure: 1. Copy the current content of the drawing buffer either to a texture, or using accumulation buffer 2. Clear the scene 3. Render the quad(s) to the buffer 4. Copy the content of the buffer to a texture 5. Re-render the original scene using the copy from #1 but needless to say, this involves a lot of (seemingly) un-neccesary and costful operations (mainly step #1, #2 and #5. There HAS to be some better way to achieve this? I have been looking into using framebuffer objects, and although it seems quite like something I could use, my current graphics card are pretty little exciting (and is missing the framebuffer_object extension). Any hints? :) Thanks in advance! Best regards, Hallgeir

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If your card doesn't have the GL_EXT_framebuffer_object extension, you can't do things the easy way, but you may be able to do them the hard way. Do you have the WGL_ARB_pbuffer extension? (Note: You'll need to get that using the wglGetExtensionsStringARB func.)

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I'm guessing the WGL_* stuff are windows specific? Because I have no WGL_ extensions (I use Linux (more accurately, Ubuntu 9.04)). I do however have support for a bunch of GLX_ extensions, among those, the GLX_SGIX_pbuffer extension. Can I assume that it is the same as the WGL_EXT_pbuffer extension?

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Quote:
Original post by hallgeir
I do however have support for a bunch of GLX_ extensions, among those, the GLX_SGIX_pbuffer extension. Can I assume that it is the same as the WGL_EXT_pbuffer extension?
It's the same inasmuch as it does the same sort of thing and is similarly painful compared to FBOs, yes. [grin] That's what you'll want to play with. It's basically a way to create a wholly separate GLX context, one which draws into something that can become a texture directly, with no copying.

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