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Submitted by Ben Clayton, posted on September 05, 2003




Image Description, by Ben Clayton



For the last year I've been building my own engine to research into the new effects used in the next generation games, i.e. Doom3. One effect I was interested in was bump-mapping. I decided to give a shot at trying to reproduce the way that Doom3 calculated it's normal maps from high detailed models, to then be placed on a much lower resolution model.

My method uses the Object-Orientated normal map approach. Like most bump-mapping techniques, this approach requires a unique triangle on the normal map per face, so reusing the UV mapping from any texture mapping would not always work. So what I needed was to create a separate normal UV mapping for the model. The normal UV mapping could be created by hand in a modelling program such as 3DS Max, but I liked the idea of writing an Unwrapper, so here it is.

Unlike most unwrappers that already exist; the unwrapper does not try to keep faces that are neighbours on the model as neighbours on the UV map. Why? Because there's no need to. The UV mapping would only be used internally, with no need for any human to try and understand which triangle relates to which face.

So the result is this UV-unwrapper. The method of unwrapping is quite a complicated one, but is basically an ever growing polygon, which uses a horrendously complicated edge matching function to find where to place the next triangle. The white lines you see are the edge of this polygon. By placing the largest triangles first, any gaps formed in the polygon are usually pretty well filled by smaller triangles later on, meaning quite an efficient normal map.

The model in this picture was around 800 polygons, and took about 2 minutes to unwrap. I feel there is more optimisation to follow! Thanks for reading.

Ben Clayton.


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