Blender Git Loki

CMake: Keep unconditional code together.

Review update: Fix exporter UI issues:

Simplify frame correction logic.

Not reset bitflags checkbox.

Use INT_MIN, not -INT_MAX.

Simplify tool-tips.

Review update: fix UI text; add comments.

Variable type change for `forward_axis` and `up_axis`.

Minor fixes, use scoped_timer for export too.

Export loop normals not vertex normals.

Don't write default scale and translation.

Also fix debug warning of material not found.

Add asserts to catch unchanged values.

Cleanup: comments and rna warning.

Not expose MPoly to writer. Write normals correctly

Write vertex normals only of smooth shaded polygons, otherwise
write face normals.

Keep normal indices in writer only since OBJMesh doesn't need to know
about export parameters. (will remove more such items from OBJMesh
later on.)

Keep MPoly related operations inside OBJMesh only & don't expose it to
Writer.

Hide Nurb from Writer. Rename OBJNurbs as per object type.

Add exporter specific code.

Files like `io_obj.c` which contain both importer and exporter code
are also here.

Differential Revision: https://developer.blender.org/D8754

Fix UI tooltips, layout, frame setting.

Fix NodetreeRef crashing due to null nodetree.

Move uv_indices in OBJMesh. Save some memory.

Since OBJMesh has dynamically allocated space in smooth groups
and uv_indices (which can be a lot), destruct objects that have
been written.

Use `const` at some places.

Remove export_params_ from OBJNurbs.

Review update: fix exporter UI.

Remove export_params_ member from OBJMesh.

Review update: use float3, std::optional, c_str()

split nurbs function into two.

Add material name append if material groups are specified.

fix smooth groups calculation

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

Review update: fix exporter UI.

Change bsdf values as per illum values.

Set defaults of MTLMaterial that is useful for importer.
For exporter, asserts have been added.