Tweak API to support adding evaluated meshes to main database

One of the usecases is to create mesh from an object is a manner similar to
how Apply Modifiers does it, and have it in the bmain so it can be referenced
by other objects.

This usecase is something what went unnoticed in the previous API changes, so
here is a followup.

Summary of changes:

* bpy.meshes.new_from_object() behaves almost the same as before this change.
  The difference now is that it now ensures all referenced data-blocks are
	original (for example, materials referenced by the mesh).

* object.to_mesh() now creates free-standing Mesh data-block which is outside
  of any bmain. The object owns it, which guarantees the memory never leaks.

  It is possible to force free memory by calling object.to_mesh_clear().

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D4875

1 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_object_types.h b/source/blender/makesdna/DNA_object_types.h
index a73c762e3bf..0b2f3d69bd2 100644
--- a/source/blender/makesdna/DNA_object_types.h
+++ b/source/blender/makesdna/DNA_object_types.h
@@ -43,6 +43,7 @@ struct DerivedMesh;
 struct FluidsimSettings;
 struct GpencilBatchCache;
 struct Ipo;
+struct Mesh;
 struct Material;
 struct Object;
 struct PartDeflect;
@@ -160,6 +161,10 @@ typedef struct Object_Runtime {
    */
   struct Mesh *mesh_deform_eval;
 
+  /* This is a mesh representation of corresponding object.
+   * It created when Python calls `object.to_mesh()`. */
+  struct Mesh *object_as_temp_mesh;
+
   /** Runtime evaluated curve-specific data, not stored in the file. */
   struct CurveCache *curve_cache;