obj: vertex colors support in importer and exporter

Adds support for vertex colors to OBJ I/O.

Importer:

- Supports both "xyzrgb" and "MRGB" vertex color formats.
- Whenever vertex color is present in the file for a model, it is
  imported and a Color attribute is created (per-vertex, full float
  color data type). Color coming from the file is assumed to be sRGB,
  and is converted to linear upon import.

Exporter:

- Option to export the vertex colors. Defaults to "off", since not
  all 3rd party software supports vertex colors.
- When the option is "on", if a mesh has a color attribute layer,
  the active one is exported in "xyzrgb" form. If the mesh has
  per-face-corner colors, they are averaged on the vertices.
  Colors are converted from linear to sRGB upon export.

Reviewed By: Howard Trickey
Differential Revision: https://developer.blender.org/D15159

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/io/wavefront_obj/importer/obj_import_objects.hh b/source/blender/io/wavefront_obj/importer/obj_import_objects.hh
index b67ba46af03..69babc26bb0 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_objects.hh
+++ b/source/blender/io/wavefront_obj/importer/obj_import_objects.hh
@@ -26,6 +26,7 @@ struct GlobalVertices {
   Vector<float3> vertices;
   Vector<float2> uv_vertices;
   Vector<float3> vertex_normals;
+  Vector<float3> vertex_colors;
 };
 
 /**
@@ -102,6 +103,8 @@ struct Geometry {
 
   int vertex_start_ = 0;
   int vertex_count_ = 0;
+  int vertex_color_start_ = 0;
+  int vertex_color_count_ = 0;
   /** Edges written in the file in addition to (or even without polygon) elements. */
   Vector<MEdge> edges_;