RE: [Algorithms] Cubemap support
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From: Jon W. <hp...@mi...> - 2001-09-14 16:40:13
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> > Is GeForce the only card to support cube maps? (In both GL and DX) > > What I'd like to know is how much slower a cube-mapped surface is > to render > than a single textured surface? > > Surely it would be six times slower since it has to render the > object six times? No, there's only one texture fetch, which chooses between one of six simultaneously bound textures. The difference between cube map texture coordinate generation and general 2D texture coordinate generation is that the cube map math is higher order than just the single texture matrix transform (and uses normal and possibly eye ray as inputs instead of u,v). Note that cube maps are used for many other things than just environment maps. If you do a true live environment map, then the entire SCENE has to be rendered six times PER OBJECT, plus a last time for actually displaying it; this can get a tad slow. But there are other, more interesting uses of cube maps. I think most modern cards support cube mapping (if they say "EMBM" chances are good, and that started back in the Matrox G400 days :-). Whether they expose the ARB_texture_cube_map extension to OpenGL is up to the driver writers, but as it's an ARB, support is fairly widespread. (I suggest reading the spec for more details about how it's rendered). Cheers, / h+ |