Blender Git Loki

Prepend importer_ to mesh_utils; parser_ to string_utils.

Move MTLMaterial & float3_to_string to exporter files.

Keeping the branch in sync with D8754 and D8753.

Merge branch 'exporter_n' into soc-2020-io-performance

Move vertex index Vector resize to OBJMesh.

Corrections: correct wrong assert, remove cast.

Simplify material group calculation.

Simplify vertex group calculation.

Add smooth group constants, use "0" instead of "off".

Add polygon element writer selector to OBJWriter.

Add polygon normal indices calculation method to OBJMesh.

Remove depsgraph member variable; use const variables.

Material: Disambiguate mat_nr + 1.

Add method to free mesh; disambiguate triangulate method.

Create MTLWriter object early, add methods for filename and file status.

Cleanup: rename functions, use const, edit comments.

Create IndexOffsets struct instead of array[3].

Make OBJ indices one-based in Writer, not in Object processor.

Early return in a few places.

Fix two consecutive group name `g ...` lines by adding an `else`.

Remove UNUSED macro from poly elements writers.

Break MTLWriter::append_materials into two functions.

Silence unused lambda warning in release build.

Log errors in fopen and fclose.