Texture coordinates: how to calculate them?

Is there a formula that i can use to calcu开发者_如何学Clate texture coordinates for a complex object not something like cube or sphere?

The texture coordinates are usually set manually by whoever creates the model, using the modelling package.

There are ways of automating the whole process, to a great extent. The results may not be much use if somebody is going to draw the texture based on the UV coordinates, and if you ask the impossible (e.g., mapping a sphere exactly, with no distortion and no seams) then you may not get perfect results -- but for processes such as light mapping this is a common approach.

Levy's LSCM is one approach, as used in Blender, for example. See http://alice.loria.fr/index.php/publications.html?Paper=lscm@2002

Direct3D9 has a UV unwrap tool in its D3DX library; I'm not sure what algorithm it uses, and the documentation isn't amazing, but it does work. See http://msdn.microsoft.com/en-us/library/bb206321(VS.85).aspx

(Most 3D modelling packages have some kind of automated UV unwrap, too, but in general they never seem to have had too much time spent on them. Presumably the expectation is that somebody will want to go through and fix it up by hand afterwards anyway.)