Blender Git Loki

Depsgraph: Hook up constraints evaluation callback

Quite straightforward. There's one extra flag to the old object where_is
which helps preventing duplicated code needed for old dependency graph
system In the future we'll get rid of this argument and decouple all the
functions in a nice way.

One retarded issue is setting negative scale flag on the object, which
currently happens in both local transform and constraints update.

Bigger issue here is the original object matrix which should be used
as an input for the constraints stack. Currently constraints will operate
on the previous final object matrix when changing the dependencies of the
constraint list.

This is possible to solve by storing intermediate data in the graph
(or somewhere else(, but for until that's nicely implemented we'll probably
couple constraints back. Will investigate this further.