Fix T41019: Calculate Mass does not calculate actual volume.

This was a ToDo item, for mesh-based rigid body shapes (trimesh, convex)
the operator was simply using the bounding box volume, which can grossly
overestimate the volume and mass.

Calculating the actual volume of a mesh is not so difficult after all,
see e.g.
http://research.microsoft.com/en-us/um/people/chazhang/publications/icip01_ChaZhang.pdf

This patch also allows calculating the center-of-mass in the same way.
This is currently unused, because the rigid body system assumes the CoM
to be the same as the geometric object center. This is fine most of the
time, adding such user settings for "center-of-mass offset" would also
add quite a bit of complexity in user space, but it could be necessary
at some point. A number of other physical properties could be calculated
using the same principle, e.g. the moment of inertia.

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_rigidbody.h b/source/blender/blenkernel/BKE_rigidbody.h
index 86be3bfe770..c946f3ac9e8 100644
--- a/source/blender/blenkernel/BKE_rigidbody.h
+++ b/source/blender/blenkernel/BKE_rigidbody.h
@@ -69,6 +69,9 @@ void BKE_rigidbody_world_groups_relink(struct RigidBodyWorld *rbw);
 /* 'validate' (i.e. make new or replace old) Physics-Engine objects */
 void BKE_rigidbody_validate_sim_world(struct Scene *scene, struct RigidBodyWorld *rbw, bool rebuild);
 
+void BKE_rigidbody_calc_volume(struct Object *ob, float *r_vol);
+void BKE_rigidbody_calc_center_of_mass(struct Object *ob, float r_com[3]);
+
 /* -------------- */
 /* Utilities */