Environment Maps ?

Hi !!

An environment map is nothing else than a normal texture. Environment mapping is a different algo than texture mapping. Normal texture mapped objects have fixed UV (so texture coordinates) for every vertex. They do not change even when they are rotated.
With environment mapping, the uv's are changing when you rotate the object. So the uv's are fixed by the environment. The best example would be a sphere. While with normal texture mapping you would see the texture of different sides when you rotate the sphere (imagine a sphere with an earth texture map, first you see Europe than america, then asia, india, and so on). With Environment mapping you always see Europe even when you rotate the object, because the uv's aren't fixed to the object but fixed to the environment. I hope this is understandable.
This is normally used to create great mirror and specular lighting effects.
I hope this helps.

Phillip

Hi, I think (but I'm not sure) that an environment map is also used for 3D "backdrops". The best example I can think of is the sky textures in Quake2. The sky texture moves differently than the other textures b/c it's in the background. Someone please correct me on this if I'm wrong.

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<Diego>

The term usually refers to what Phillip describes (with an added notice that the UV texture coordinates are generated based on the vertex normals).

Quake2's background was a skybox, so no texture coordinate generation going on there. Without going to deep into it, a skybox is a cube mapped with textures taken from an environment rendered with 180 FOV. When it's projected in the scene, it's projected to infinity (no depth writes) and rotates with the viewpoint.

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Scott Franke [druid-]
sfranke@usc.edu
druid-'s GL Journal
http://www.gamedev.net/opengl