This patch adds the ability to the subsurf modifier and the multires modifier to preserve and interpolate a models custom normals.
- It checks that the object has custom normals, the option turned on, and auto_smooth checked.
- If it does it calculates the custom normals on the input mesh and removes the CD_FLAG_TEMPORARY flag form the CD_NORMAL custom data layer.
- The subsurf calculation then takes care of the interpolation.
- Then at the end it assigns the custom normals to the result mesh and sets the CD_FLAG_TEMPORARY back onto both meshes.
- For multires modifier it turns off the custom normals when in sculpt mode.