CommonFilters - some new filters, and the future

Ok.

In the meantime, could you check this one first?

bugs.launchpad.net/panda3d/+bug/1214782

It’s a very small patch that only fixes the bug that prevented double-threshold light ramps from working in 1.8.1. It would be ideal to base the new features on a source tree that has this fixed.

After the bugfix, my plan of action:

  • Separate the getTexCoordSemantic() change from the rest
  • Modularize CommonFilters (refactor only; no functional changes at this point)
  • Add new cartoon shader (includes changes to both shader generator and CommonFilters)
  • Add these new filters to CommonFilters (maybe one by one?)