mirror

a technique called projective textureing is commenly used for this task. also, a VERY expensive hack is to draw all geometry twice. suppose I got a world, and the ground level is the y = 0 plane, suppse you also have a lake on the ground level, simply draw the lake as a open shape(no cover like a hole in the ground) and draw all the geometry again but with the y values negated ie scale the y direction by -1. this is just a stupid fun thing to do. if you're doing a serious project you should use projective texturing, as that is much faster and can easily be modified to fake the wavey like textures in the water, like in half life 2.

check out this link
http://www.gamedev.net/reference/articles/article2138.asp

Tim

@Timw:
I don´t know exactly, but I would say you don´t get around that "hack" even with projective texturing? I mean, projective texturing is nice, but you need some texture to project, and that texture is normally generated in kind of reflection "pre-pass", where you do the same thing you described as "hack", namely rendering the whole scene mirrored at the plane, but saving the result to the texture you later on project onto the water plane. Am I mistaken?

I thought of that right after I did the post lol. ya they're both similiar I guess. the other approach is done in one pass, but I dont know which would be faster. the projective textureing is still much more flexible with regards to the special effects you can do wtih it, also, you could calculate frenel stuff, anyone know which is faster for pure mirror reflecitons?

For a pure planar mirror, I would have expected a stencil-based technique to be the most efficient. No point rendering it all into a texture if you're only going to render that texture out as a quad.