Disabled the velocity filtering feature for now, since the weighting is

incorrect.

The voxel grid needs better tool support to make it usable, so fixing
the filtering is not high priority right now.

source/blender/physics/intern/BPH_mass_spring.cpp

@@ -431,8 +431,10 @@ static void cloth_calc_volume_force(ClothModifierData *clmd)
 		}
 		BPH_hair_volume_normalize_vertex_grid(vertex_grid);
 		
+#if 0
 		/* apply velocity filter */
 		BPH_hair_volume_vertex_grid_filter_box(vertex_grid, clmd->sim_parms->voxel_filter_size);
+#endif
 		
 		for (i = 0; i < numverts; i++) {
 			float x[3], v[3], f[3], dfdx[3][3], dfdv[3][3];

source/blender/physics/intern/hair_volume.c

@@ -295,6 +295,7 @@ void BPH_hair_volume_normalize_vertex_grid(HairVertexGrid *grid)
 	}
 }
 
+#if 0 /* XXX weighting is incorrect, disabled for now */
 /* Velocity filter kernel
  * See http://en.wikipedia.org/wiki/Filter_%28large_eddy_simulation%29
  */
@@ -363,6 +364,7 @@ void BPH_hair_volume_vertex_grid_filter_box(HairVertexGrid *grid, int kernel_siz
 		copy_v3_v3(grid->verts[i].velocity, grid->verts[i].velocity_smooth);
 	}
 }
+#endif
 
 HairVertexGrid *BPH_hair_volume_create_vertex_grid(int res, const float gmin[3], const float gmax[3])
 {

source/blender/physics/intern/implicit.h

@@ -155,7 +155,9 @@ void BPH_hair_volume_free_vertex_grid(struct HairVertexGrid *grid);
 
 void BPH_hair_volume_add_vertex(struct HairVertexGrid *grid, const float x[3], const float v[3]);
 void BPH_hair_volume_normalize_vertex_grid(struct HairVertexGrid *grid);
+#if 0 /* XXX weighting is incorrect, disabled for now */
 void BPH_hair_volume_vertex_grid_filter_box(struct HairVertexGrid *grid, int kernel_size);
+#endif
 void BPH_hair_volume_vertex_grid_forces(struct HairVertexGrid *grid, const float x[3], const float v[3],
                                         float smoothfac, float pressurefac, float minpressure,
                                         float f[3], float dfdx[3][3], float dfdv[3][3]);