SLIM is a state of the art UV unwrapping algorithm invented at the IGL institute of ETH Zurich. Thanks to its iterative nature, it is superior to all algorithms currently implemented in Blender in the following terms:
- it can unwrap complex meshes with much less distortion (even with no seams applied).
- the user gains control over the “unwrap quality” / “computing time” tradeoff. More iterations means less distorted UV map, but more time is required to compute it.
- it can be used to effectively minimize stretch on meshes already unwrapped (Minimize Stretch operator).
Angle Based method (implemented in Blender)
First let’s take a look how the algorithms currently supported by Blender deal with unwrapping the mesh. The picture below shows a result from the Angle Based method. Note how UVs are stretched at the center and border (red color). Due to stretching the texture is unevenly laid on the mesh – compare big texture squares at the top of the head with small squares around the neck.
Conformal method (implemented in Blender)
Next picture shows a result of the second algorithm available in Blender: “Conformal”. As you can see it doesn’t do any better – there is a lot of stretching in the texture as well:
SLIM method (to be implemented in this proposal)
Now let’s check how SLIM will deal with this task. Remember that SLIM is an iterative algorithm – more iterations means better result, but also more time required to compute it. The next pictures show SLIM results after different number of iterations:
As you can see just 5 SLIM iterations is enough to achieve a less stretched UV map than the maps generated by the Blender methods. After 10 iterations, we get a map with much less distortion (the texture is laid on the mesh much more evenly). What is more 10 iterations of the algorithm can be computed in a very short time (similar to the time required for methods already implemented in Blender). When we proceed to 50 iterations, the result doesn’t change significantly, what indicates that we can stop on that number. We got a very decently unwrapped UV map with no single seam.
For more details regarding SLIM watch an Aurel’s presentation regarding his original implementation for Blender 2.7 (not merged into the official codebase): https://www.youtube.com/watch?v=PLUoLQUK3-s.