I''m trying to build a heat effect for my flight simulator ( www.web-discovery.net ). I was suggested to achieve that rendering the screen to a texture and then tweaking and warping the texture. i don''t know if i understood it correctly, but rendering to a texture means that i have to render the geometry twice, the first time to build the texture, the second time to draw on the screen. In my sim i have about 60000 triangles rendered on screen, so that would be very slow, even using the ARB extension. Right ? Advices needed ...

there are a few tweaks that accelerates the "double rendering" hassle.
The first trick being : you can get the texture for the precedent picture which has already been rendered on screen. You''re always one-frame-too-late but in general it doesn''t matter, especially for effects that distorts the picture (such as refraction in the heat effect). The other problem with this trick is that you need to get the texture from the screen, but some extensions allow to render directly in the texture (techniques known as render-to-texture) which has some advantages (slightly faster, slightly more flexible). If you''re using the render-to-texture extension, I think you have to render the scene twice. In that case, you can render a low-resolution scene (low-polygonal for instance) in the texture which will significantly speed up without lowering image quality that much.