[Bf-committers] Cloth modifier -> Field weights -> unique vertex group and weight painting for each force type

[Peter Hoppe]

In Blender, I've been experimenting with the cloth modifier. One feature I am missing is to assign weight painted vertex
groups to the resp. cloth field weights in the physics context. This sort of weighting is already possible in the "Cloth
Stiffness Scaling" in the physics section.

This would allow for setups where (for example) we have a mesh with a vertex group x which is weight painted so that x
has got a force field weight of 1 in the center and a force field weight of 0.5 in the outer parts.

In extension to this, one could make all force types in the "Cloth Field Weights" section assignable to separate vertex
groups, each one with its own weight painting. This would make setups possible where (for example) we have a mesh which
in it's center responds to a force field, weight 1), a bit outside the center it responds to a force field, weight 0.5
and in the outer rim it responds to a wind field, weight 1.

Development wise, I am happy to look into this - however, I'd need some pointers where to start:

* Which documentation do I need to consult?
* If it can be done with a plugin, which part of the plugin API do I use?
* If it needs some development below the plugin layer, which parts would I need to consider?
* Any hints of how to bind the feature into the GUI?
* I assume that this new feature would present some challenges when it comes to saving blender files - how could this
vertex group and weight paint information be incorporated?

I don't expect this to be easy to implement - it would probably involve some measure of battling it through. But it
would be a fun project for me to do, plus I'd be learning in the process. Any hints are much appreciated! At the moment
I am using Blender 2.62 on Kubuntu 12.04, 64 bit.

Thank you so much for your consideration!