Custom Character Program

Is this a 3D or 2D game? For 3D, the easiest way would probably be to assign various matrices to the seperate sections of the model (or possibly a vertex shader) then modify those appropriately.

I don't know of any online resources but I can relate some things we do in our game.

Basically character customization comes down to 3 things:
1) Meshes
2) Textures
3) Shaders

Each model is made up of several different meshes on a skeleton model (we use cal3d format. Check them out on sourceforge). So for example we can have different head/torso/leg meshes. We also have 'optional' meshes for things like beards or different hair styles.

From there we can define different textures for those meshes to give them different 'looks'. At some point we will be building dynamic textures so we can do things like tatooes on the body.

As a final step we can apply a shader to these textures so they can be many different colours/looks.

I would think on how you define your customization system would depend on what your model system/Engine supports.

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Andrew