Re: [Algorithms] Cubemap support
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From: Paul F. <pf...@at...> - 2001-09-17 09:42:00
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Jon Watte wrote: > > > 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. But surely you can see more than one of the cube reflection's faces on the surface of a reflective sphere, for example? > 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. Sure, like per-pixel lighting. I'd have thought that dual-peraboloid would be faster and more correct (less distortion) than cube-mapping for that kind of thing? > 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). Do you have any references for the definitive rendering algorithm for cube-mapping? I can only find very vague stuff. Actually, whilest I'm at it, do you know of any references for EMBM - I thought only cards which could do dependent texture reads were capable of EMBM? Cheers, Paul. |