Blender Git Loki

Speedup for constraints update from python script

General idea is to avoid actual calculation from property update()
callback and tag things for update later instead.

That said, pose constraint flags are now tagged for update and
handled as a part of object update. In the new depsgraph it'll
be a nice dedicated operation node.

Also avoid updating disabled flags for all the modifiers. This
part of the path is not totally optimal since it'll still need
to iterate over bones in order to get pchan, but to optimize it
further would be nice to find a way to avoid pchan requirement
all together.

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D1191