Blender Git Loki

Avoid double matrix multiplication.

Also build transforms with no children as empties.

Camera reader: avoid reading props twice, fix for zero'd clip start.

De-duplicate matrix reading code.

Fix camera reader not using the right time for sampling.

Merge branch 'master' into alembic_basic_io

Setting up transform hierarchy for animated data somewhat works.

There is still some work to be done as in some cases the transform
appears to be mirrored. Though most test files seem to be imported
correctly.

Remove debug print.

Fix missing depsgraph update of new constraint.

Only covers old depsgraph for now.

Move addition of constraint to object class.

Avoid adding modifiers when the data is constant.

Added a new 'Transform Cache' constraint to lookup transformation
matrices from alembic archives.

Fix compile error on Windows.

Fix curve using editnurbs in object mode.

Merge branch 'master' into alembic_basic_io

Initial support to import hair systems.

For the time being, hair are read as curves since this is how alembic
stores them. And since there is no real way to know if an ICurves object
exported from another software is a hair system or not, it will probably
stay like so.

Fix crash when exporting a hair system.

Crash was due to accessing hair data from another thread (through the
export job).

Revert changes done to the transform matrix read/write and axis
conversion code to the state of the original patch.

The rewrite wasn't ideal, and prone to bugs. The idea was to not
hardcode Y-up <-> Z-up conversions but rather let the user choose the
axis during the export/import process, but since the other DCCs commonly
found in VFX pipeline all use a Y-up system, hardcoding everything
should be fine for the time being. This will probably be revisited in
the future if need be.

Merge branch 'master' into alembic_basic_io

Cleanup: const correctness.