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, 4 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_mesh.h b/source/blender/blenkernel/BKE_mesh.h
index 587dea5095c..975a8fd63df 100644
--- a/source/blender/blenkernel/BKE_mesh.h
+++ b/source/blender/blenkernel/BKE_mesh.h
@@ -212,6 +212,10 @@ bool BKE_mesh_center_median(struct Mesh *me, float cent[3]);
 bool BKE_mesh_center_bounds(struct Mesh *me, float cent[3]);
 bool BKE_mesh_center_centroid(struct Mesh *me, float cent[3]);
 
+void BKE_mesh_calc_volume(struct MVert *mverts, int numVerts,
+                          struct MFace *mfaces, int numFaces,
+                          float *r_vol, float *r_com);
+
 /* tessface */
 void BKE_mesh_loops_to_mface_corners(
         struct CustomData *fdata, struct CustomData *ldata,