Hair volume calculation is now in its own file.

Code is currently disabled until the other main forces are in place.

3 files changed, 486 insertions, 447 deletions

diff --git a/source/blender/physics/CMakeLists.txt b/source/blender/physics/CMakeLists.txt
index b08cf177f44..5df32c2ea32 100644
--- a/source/blender/physics/CMakeLists.txt
+++ b/source/blender/physics/CMakeLists.txt
@@ -41,6 +41,7 @@ set(INC_SYS
 set(SRC
 	intern/BPH_mass_spring.cpp
 	intern/ConstrainedConjugateGradient.h
+	intern/hair_volume.c
 	intern/implicit.h
 	intern/implicit_blender.c
 	intern/implicit_eigen.cpp
diff --git a/source/blender/physics/intern/hair_volume.c b/source/blender/physics/intern/hair_volume.c
new file mode 100644
index 00000000000..5111eac3a48
--- /dev/null
+++ b/source/blender/physics/intern/hair_volume.c
@@ -0,0 +1,483 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) Blender Foundation
+ * All rights reserved.
+ *
+ * The Original Code is: all of this file.
+ *
+ * Contributor(s): Janne Karhu, Lukas Toenne
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+/** \file blender/blenkernel/intern/hair_volume.c
+ *  \ingroup bph
+ */
+
+#include "BLI_math.h"
+#include "BLI_utildefines.h"
+
+#if 0 // XXX TODO
+
+/* ================ Volumetric Hair Interaction ================
+ * adapted from
+ *      Volumetric Methods for Simulation and Rendering of Hair
+ *      by Lena Petrovic, Mark Henne and John Anderson
+ *      Pixar Technical Memo #06-08, Pixar Animation Studios
+ */
+
+/* Note about array indexing:
+ * Generally the arrays here are one-dimensional.
+ * The relation between 3D indices and the array offset is
+ *   offset = x + res_x * y + res_y * z
+ */
+
+/* TODO: This is an initial implementation and should be made much better in due time.
+ * What should at least be implemented is a grid size parameter and a smoothing kernel
+ * for bigger grids.
+ */
+
+/* 10x10x10 grid gives nice initial results */
+static const int hair_grid_res = 10;
+
+static int hair_grid_size(int res)
+{
+	return res * res * res;
+}
+
+BLI_INLINE void hair_grid_get_scale(int res, const float gmin[3], const float gmax[3], float scale[3])
+{
+	sub_v3_v3v3(scale, gmax, gmin);
+	mul_v3_fl(scale, 1.0f / (res-1));
+}
+
+typedef struct HairGridVert {
+	float velocity[3];
+	float density;
+} HairGridVert;
+
+#define HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, axis) ( min_ii( max_ii( (int)((vec[axis] - gmin[axis]) / scale[axis]), 0), res-2 ) )
+
+BLI_INLINE int hair_grid_offset(const float vec[3], int res, const float gmin[3], const float scale[3])
+{
+	int i, j, k;
+	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
+	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
+	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
+	return i + (j + k*res)*res;
+}
+
+BLI_INLINE int hair_grid_interp_weights(int res, const float gmin[3], const float scale[3], const float vec[3], float uvw[3])
+{
+	int i, j, k, offset;
+	
+	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
+	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
+	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
+	offset = i + (j + k*res)*res;
+	
+	uvw[0] = (vec[0] - gmin[0]) / scale[0] - (float)i;
+	uvw[1] = (vec[1] - gmin[1]) / scale[1] - (float)j;
+	uvw[2] = (vec[2] - gmin[2]) / scale[2] - (float)k;
+	
+	return offset;
+}
+
+BLI_INLINE void hair_grid_interpolate(const HairGridVert *grid, int res, const float gmin[3], const float scale[3], const float vec[3],
+                                      float *density, float velocity[3], float density_gradient[3])
+{
+	HairGridVert data[8];
+	float uvw[3], muvw[3];
+	int res2 = res * res;
+	int offset;
+	
+	offset = hair_grid_interp_weights(res, gmin, scale, vec, uvw);
+	muvw[0] = 1.0f - uvw[0];
+	muvw[1] = 1.0f - uvw[1];
+	muvw[2] = 1.0f - uvw[2];
+	
+	data[0] = grid[offset           ];
+	data[1] = grid[offset         +1];
+	data[2] = grid[offset     +res  ];
+	data[3] = grid[offset     +res+1];
+	data[4] = grid[offset+res2      ];
+	data[5] = grid[offset+res2    +1];
+	data[6] = grid[offset+res2+res  ];
+	data[7] = grid[offset+res2+res+1];
+	
+	if (density) {
+		*density = muvw[2]*( muvw[1]*( muvw[0]*data[0].density + uvw[0]*data[1].density )   +
+		                      uvw[1]*( muvw[0]*data[2].density + uvw[0]*data[3].density ) ) +
+		            uvw[2]*( muvw[1]*( muvw[0]*data[4].density + uvw[0]*data[5].density )   +
+		                      uvw[1]*( muvw[0]*data[6].density + uvw[0]*data[7].density ) );
+	}
+	if (velocity) {
+		int k;
+		for (k = 0; k < 3; ++k) {
+			velocity[k] = muvw[2]*( muvw[1]*( muvw[0]*data[0].velocity[k] + uvw[0]*data[1].velocity[k] )   +
+			                         uvw[1]*( muvw[0]*data[2].velocity[k] + uvw[0]*data[3].velocity[k] ) ) +
+			               uvw[2]*( muvw[1]*( muvw[0]*data[4].velocity[k] + uvw[0]*data[5].velocity[k] )   +
+			                         uvw[1]*( muvw[0]*data[6].velocity[k] + uvw[0]*data[7].velocity[k] ) );
+		}
+	}
+	if (density_gradient) {
+		density_gradient[0] = muvw[1] * muvw[2] * ( data[0].density - data[1].density ) +
+		                       uvw[1] * muvw[2] * ( data[2].density - data[3].density ) +
+		                      muvw[1] *  uvw[2] * ( data[4].density - data[5].density ) +
+		                       uvw[1] *  uvw[2] * ( data[6].density - data[7].density );
+		
+		density_gradient[1] = muvw[2] * muvw[0] * ( data[0].density - data[2].density ) +
+		                       uvw[2] * muvw[0] * ( data[4].density - data[6].density ) +
+		                      muvw[2] *  uvw[0] * ( data[1].density - data[3].density ) +
+		                       uvw[2] *  uvw[0] * ( data[5].density - data[7].density );
+		
+		density_gradient[2] = muvw[2] * muvw[0] * ( data[0].density - data[4].density ) +
+		                       uvw[2] * muvw[0] * ( data[1].density - data[5].density ) +
+		                      muvw[2] *  uvw[0] * ( data[2].density - data[6].density ) +
+		                       uvw[2] *  uvw[0] * ( data[3].density - data[7].density );
+	}
+}
+
+static void hair_velocity_smoothing(const HairGridVert *hairgrid, const float gmin[3], const float scale[3], float smoothfac,
+                                    lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
+{
+	int v;
+	/* calculate forces */
+	for (v = 0; v < numverts; v++) {
+		float density, velocity[3];
+		
+		hair_grid_interpolate(hairgrid, hair_grid_res, gmin, scale, lX[v], &density, velocity, NULL);
+		
+		sub_v3_v3(velocity, lV[v]);
+		madd_v3_v3fl(lF[v], velocity, smoothfac);
+	}
+}
+
+static void hair_velocity_collision(const HairGridVert *collgrid, const float gmin[3], const float scale[3], float collfac,
+                                    lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
+{
+	int v;
+	/* calculate forces */
+	for (v = 0; v < numverts; v++) {
+		int offset = hair_grid_offset(lX[v], hair_grid_res, gmin, scale);
+		
+		if (collgrid[offset].density > 0.0f) {
+			lF[v][0] += collfac * (collgrid[offset].velocity[0] - lV[v][0]);
+			lF[v][1] += collfac * (collgrid[offset].velocity[1] - lV[v][1]);
+			lF[v][2] += collfac * (collgrid[offset].velocity[2] - lV[v][2]);
+		}
+	}
+}
+
+static void hair_pressure_force(const HairGridVert *hairgrid, const float gmin[3], const float scale[3], float pressurefac, float minpressure,
+                                lfVector *lF, lfVector *lX, unsigned int numverts)
+{
+	int v;
+	
+	/* calculate forces */
+	for (v = 0; v < numverts; v++) {
+		float density, gradient[3], gradlen;
+		
+		hair_grid_interpolate(hairgrid, hair_grid_res, gmin, scale, lX[v], &density, NULL, gradient);
+		
+		gradlen = normalize_v3(gradient) - minpressure;
+		if (gradlen < 0.0f)
+			continue;
+		mul_v3_fl(gradient, gradlen);
+		
+		madd_v3_v3fl(lF[v], gradient, pressurefac);
+	}
+}
+
+static void hair_volume_get_boundbox(lfVector *lX, unsigned int numverts, float gmin[3], float gmax[3])
+{
+	int i;
+	
+	INIT_MINMAX(gmin, gmax);
+	for (i = 0; i < numverts; i++)
+		DO_MINMAX(lX[i], gmin, gmax);
+}
+
+BLI_INLINE bool hair_grid_point_valid(const float vec[3], float gmin[3], float gmax[3])
+{
+	return !(vec[0] < gmin[0] || vec[1] < gmin[1] || vec[2] < gmin[2] ||
+	         vec[0] > gmax[0] || vec[1] > gmax[1] || vec[2] > gmax[2]);
+}
+
+BLI_INLINE float dist_tent_v3f3(const float a[3], float x, float y, float z)
+{
+	float w = (1.0f - fabsf(a[0] - x)) * (1.0f - fabsf(a[1] - y)) * (1.0f - fabsf(a[2] - z));
+	return w;
+}
+
+/* returns the grid array offset as well to avoid redundant calculation */
+static int hair_grid_weights(int res, const float gmin[3], const float scale[3], const float vec[3], float weights[8])
+{
+	int i, j, k, offset;
+	float uvw[3];
+	
+	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
+	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
+	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
+	offset = i + (j + k*res)*res;
+	
+	uvw[0] = (vec[0] - gmin[0]) / scale[0];
+	uvw[1] = (vec[1] - gmin[1]) / scale[1];
+	uvw[2] = (vec[2] - gmin[2]) / scale[2];
+	
+	weights[0] = dist_tent_v3f3(uvw, (float)i    , (float)j    , (float)k    );
+	weights[1] = dist_tent_v3f3(uvw, (float)(i+1), (float)j    , (float)k    );
+	weights[2] = dist_tent_v3f3(uvw, (float)i    , (float)(j+1), (float)k    );
+	weights[3] = dist_tent_v3f3(uvw, (float)(i+1), (float)(j+1), (float)k    );
+	weights[4] = dist_tent_v3f3(uvw, (float)i    , (float)j    , (float)(k+1));
+	weights[5] = dist_tent_v3f3(uvw, (float)(i+1), (float)j    , (float)(k+1));
+	weights[6] = dist_tent_v3f3(uvw, (float)i    , (float)(j+1), (float)(k+1));
+	weights[7] = dist_tent_v3f3(uvw, (float)(i+1), (float)(j+1), (float)(k+1));
+	
+	return offset;
+}
+
+static HairGridVert *hair_volume_create_hair_grid(ClothModifierData *clmd, lfVector *lX, lfVector *lV, unsigned int numverts)
+{
+	int res = hair_grid_res;
+	int size = hair_grid_size(res);
+	HairGridVert *hairgrid;
+	float gmin[3], gmax[3], scale[3];
+	/* 2.0f is an experimental value that seems to give good results */
+	float smoothfac = 2.0f * clmd->sim_parms->velocity_smooth;
+	unsigned int	v = 0;
+	int	            i = 0;
+
+	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
+	hair_grid_get_scale(res, gmin, gmax, scale);
+
+	hairgrid = MEM_mallocN(sizeof(HairGridVert) * size, "hair voxel data");
+
+	/* initialize grid */
+	for (i = 0; i < size; ++i) {
+		zero_v3(hairgrid[i].velocity);
+		hairgrid[i].density = 0.0f;
+	}
+
+	/* gather velocities & density */
+	if (smoothfac > 0.0f) {
+		for (v = 0; v < numverts; v++) {
+			float *V = lV[v];
+			float weights[8];
+			int di, dj, dk;
+			int offset;
+			
+			if (!hair_grid_point_valid(lX[v], gmin, gmax))
+				continue;
+			
+			offset = hair_grid_weights(res, gmin, scale, lX[v], weights);
+			
+			for (di = 0; di < 2; ++di) {
+				for (dj = 0; dj < 2; ++dj) {
+					for (dk = 0; dk < 2; ++dk) {
+						int voffset = offset + di + (dj + dk*res)*res;
+						int iw = di + dj*2 + dk*4;
+						
+						hairgrid[voffset].density += weights[iw];
+						madd_v3_v3fl(hairgrid[voffset].velocity, V, weights[iw]);
+					}
+				}
+			}
+		}
+	}
+
+	/* divide velocity with density */
+	for (i = 0; i < size; i++) {
+		float density = hairgrid[i].density;
+		if (density > 0.0f)
+			mul_v3_fl(hairgrid[i].velocity, 1.0f/density);
+	}
+	
+	return hairgrid;
+}
+
+
+static HairGridVert *hair_volume_create_collision_grid(ClothModifierData *clmd, lfVector *lX, unsigned int numverts)
+{
+	int res = hair_grid_res;
+	int size = hair_grid_size(res);
+	HairGridVert *collgrid;
+	ListBase *colliders;
+	ColliderCache *col = NULL;
+	float gmin[3], gmax[3], scale[3];
+	/* 2.0f is an experimental value that seems to give good results */
+	float collfac = 2.0f * clmd->sim_parms->collider_friction;
+	unsigned int	v = 0;
+	int	            i = 0;
+
+	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
+	hair_grid_get_scale(res, gmin, gmax, scale);
+
+	collgrid = MEM_mallocN(sizeof(HairGridVert) * size, "hair collider voxel data");
+
+	/* initialize grid */
+	for (i = 0; i < size; ++i) {
+		zero_v3(collgrid[i].velocity);
+		collgrid[i].density = 0.0f;
+	}
+
+	/* gather colliders */
+	colliders = get_collider_cache(clmd->scene, NULL, NULL);
+	if (colliders && collfac > 0.0f) {
+		for (col = colliders->first; col; col = col->next) {
+			MVert *loc0 = col->collmd->x;
+			MVert *loc1 = col->collmd->xnew;
+			float vel[3];
+			float weights[8];
+			int di, dj, dk;
+			
+			for (v=0; v < col->collmd->numverts; v++, loc0++, loc1++) {
+				int offset;
+				
+				if (!hair_grid_point_valid(loc1->co, gmin, gmax))
+					continue;
+				
+				offset = hair_grid_weights(res, gmin, scale, lX[v], weights);
+				
+				sub_v3_v3v3(vel, loc1->co, loc0->co);
+				
+				for (di = 0; di < 2; ++di) {
+					for (dj = 0; dj < 2; ++dj) {
+						for (dk = 0; dk < 2; ++dk) {
+							int voffset = offset + di + (dj + dk*res)*res;
+							int iw = di + dj*2 + dk*4;
+							
+							collgrid[voffset].density += weights[iw];
+							madd_v3_v3fl(collgrid[voffset].velocity, vel, weights[iw]);
+						}
+					}
+				}
+			}
+		}
+	}
+	free_collider_cache(&colliders);
+
+	/* divide velocity with density */
+	for (i = 0; i < size; i++) {
+		float density = collgrid[i].density;
+		if (density > 0.0f)
+			mul_v3_fl(collgrid[i].velocity, 1.0f/density);
+	}
+	
+	return collgrid;
+}
+
+static void hair_volume_forces(ClothModifierData *clmd, lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
+{
+	HairGridVert *hairgrid, *collgrid;
+	float gmin[3], gmax[3], scale[3];
+	/* 2.0f is an experimental value that seems to give good results */
+	float smoothfac = 2.0f * clmd->sim_parms->velocity_smooth;
+	float collfac = 2.0f * clmd->sim_parms->collider_friction;
+	float pressfac = clmd->sim_parms->pressure;
+	float minpress = clmd->sim_parms->pressure_threshold;
+	
+	if (smoothfac <= 0.0f && collfac <= 0.0f && pressfac <= 0.0f)
+		return;
+	
+	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
+	hair_grid_get_scale(hair_grid_res, gmin, gmax, scale);
+	
+	hairgrid = hair_volume_create_hair_grid(clmd, lX, lV, numverts);
+	collgrid = hair_volume_create_collision_grid(clmd, lX, numverts);
+	
+	hair_velocity_smoothing(hairgrid, gmin, scale, smoothfac, lF, lX, lV, numverts);
+	hair_velocity_collision(collgrid, gmin, scale, collfac, lF, lX, lV, numverts);
+	hair_pressure_force(hairgrid, gmin, scale, pressfac, minpress, lF, lX, numverts);
+	
+	MEM_freeN(hairgrid);
+	MEM_freeN(collgrid);
+}
+
+#if 0
+bool implicit_hair_volume_get_texture_data(Object *UNUSED(ob), ClothModifierData *clmd, ListBase *UNUSED(effectors), VoxelData *vd)
+{
+	lfVector *lX, *lV;
+	HairGridVert *hairgrid/*, *collgrid*/;
+	int numverts;
+	int totres, i;
+	int depth;
+
+	if (!clmd->clothObject || !clmd->clothObject->implicit)
+		return false;
+
+	lX = clmd->clothObject->implicit->X;
+	lV = clmd->clothObject->implicit->V;
+	numverts = clmd->clothObject->numverts;
+
+	hairgrid = hair_volume_create_hair_grid(clmd, lX, lV, numverts);
+//	collgrid = hair_volume_create_collision_grid(clmd, lX, numverts);
+
+	vd->resol[0] = hair_grid_res;
+	vd->resol[1] = hair_grid_res;
+	vd->resol[2] = hair_grid_res;
+	
+	totres = hair_grid_size(hair_grid_res);
+	
+	if (vd->hair_type == TEX_VD_HAIRVELOCITY) {
+		depth = 4;
+		vd->data_type = TEX_VD_RGBA_PREMUL;
+	}
+	else {
+		depth = 1;
+		vd->data_type = TEX_VD_INTENSITY;
+	}
+	
+	if (totres > 0) {
+		vd->dataset = (float *)MEM_mapallocN(sizeof(float) * depth * (totres), "hair volume texture data");
+		
+		for (i = 0; i < totres; ++i) {
+			switch (vd->hair_type) {
+				case TEX_VD_HAIRDENSITY:
+					vd->dataset[i] = hairgrid[i].density;
+					break;
+				
+				case TEX_VD_HAIRRESTDENSITY:
+					vd->dataset[i] = 0.0f; // TODO
+					break;
+				
+				case TEX_VD_HAIRVELOCITY:
+					vd->dataset[i + 0*totres] = hairgrid[i].velocity[0];
+					vd->dataset[i + 1*totres] = hairgrid[i].velocity[1];
+					vd->dataset[i + 2*totres] = hairgrid[i].velocity[2];
+					vd->dataset[i + 3*totres] = len_v3(hairgrid[i].velocity);
+					break;
+				
+				case TEX_VD_HAIRENERGY:
+					vd->dataset[i] = 0.0f; // TODO
+					break;
+			}
+		}
+	}
+	else {
+		vd->dataset = NULL;
+	}
+	
+	MEM_freeN(hairgrid);
+//	MEM_freeN(collgrid);
+	
+	return true;
+}
+#endif
+
+#endif
diff --git a/source/blender/physics/intern/implicit_blender.c b/source/blender/physics/intern/implicit_blender.c
index 04837bca7d1..90d7eee57cb 100644
--- a/source/blender/physics/intern/implicit_blender.c
+++ b/source/blender/physics/intern/implicit_blender.c
@@ -1567,452 +1567,6 @@ static float calculateVertexWindForce(const float wind[3], const float vertexnor
 	return dot_v3v3(wind, vertexnormal);
 }
 
-/* ================ Volumetric Hair Interaction ================
- * adapted from
- *      Volumetric Methods for Simulation and Rendering of Hair
- *      by Lena Petrovic, Mark Henne and John Anderson
- *      Pixar Technical Memo #06-08, Pixar Animation Studios
- */
-
-/* Note about array indexing:
- * Generally the arrays here are one-dimensional.
- * The relation between 3D indices and the array offset is
- *   offset = x + res_x * y + res_y * z
- */
-
-/* TODO: This is an initial implementation and should be made much better in due time.
- * What should at least be implemented is a grid size parameter and a smoothing kernel
- * for bigger grids.
- */
-
-/* 10x10x10 grid gives nice initial results */
-static const int hair_grid_res = 10;
-
-static int hair_grid_size(int res)
-{
-	return res * res * res;
-}
-
-BLI_INLINE void hair_grid_get_scale(int res, const float gmin[3], const float gmax[3], float scale[3])
-{
-	sub_v3_v3v3(scale, gmax, gmin);
-	mul_v3_fl(scale, 1.0f / (res-1));
-}
-
-typedef struct HairGridVert {
-	float velocity[3];
-	float density;
-} HairGridVert;
-
-#define HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, axis) ( min_ii( max_ii( (int)((vec[axis] - gmin[axis]) / scale[axis]), 0), res-2 ) )
-
-BLI_INLINE int hair_grid_offset(const float vec[3], int res, const float gmin[3], const float scale[3])
-{
-	int i, j, k;
-	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
-	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
-	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
-	return i + (j + k*res)*res;
-}
-
-BLI_INLINE int hair_grid_interp_weights(int res, const float gmin[3], const float scale[3], const float vec[3], float uvw[3])
-{
-	int i, j, k, offset;
-	
-	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
-	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
-	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
-	offset = i + (j + k*res)*res;
-	
-	uvw[0] = (vec[0] - gmin[0]) / scale[0] - (float)i;
-	uvw[1] = (vec[1] - gmin[1]) / scale[1] - (float)j;
-	uvw[2] = (vec[2] - gmin[2]) / scale[2] - (float)k;
-	
-	return offset;
-}
-
-BLI_INLINE void hair_grid_interpolate(const HairGridVert *grid, int res, const float gmin[3], const float scale[3], const float vec[3],
-                                      float *density, float velocity[3], float density_gradient[3])
-{
-	HairGridVert data[8];
-	float uvw[3], muvw[3];
-	int res2 = res * res;
-	int offset;
-	
-	offset = hair_grid_interp_weights(res, gmin, scale, vec, uvw);
-	muvw[0] = 1.0f - uvw[0];
-	muvw[1] = 1.0f - uvw[1];
-	muvw[2] = 1.0f - uvw[2];
-	
-	data[0] = grid[offset           ];
-	data[1] = grid[offset         +1];
-	data[2] = grid[offset     +res  ];
-	data[3] = grid[offset     +res+1];
-	data[4] = grid[offset+res2      ];
-	data[5] = grid[offset+res2    +1];
-	data[6] = grid[offset+res2+res  ];
-	data[7] = grid[offset+res2+res+1];
-	
-	if (density) {
-		*density = muvw[2]*( muvw[1]*( muvw[0]*data[0].density + uvw[0]*data[1].density )   +
-		                      uvw[1]*( muvw[0]*data[2].density + uvw[0]*data[3].density ) ) +
-		            uvw[2]*( muvw[1]*( muvw[0]*data[4].density + uvw[0]*data[5].density )   +
-		                      uvw[1]*( muvw[0]*data[6].density + uvw[0]*data[7].density ) );
-	}
-	if (velocity) {
-		int k;
-		for (k = 0; k < 3; ++k) {
-			velocity[k] = muvw[2]*( muvw[1]*( muvw[0]*data[0].velocity[k] + uvw[0]*data[1].velocity[k] )   +
-			                         uvw[1]*( muvw[0]*data[2].velocity[k] + uvw[0]*data[3].velocity[k] ) ) +
-			               uvw[2]*( muvw[1]*( muvw[0]*data[4].velocity[k] + uvw[0]*data[5].velocity[k] )   +
-			                         uvw[1]*( muvw[0]*data[6].velocity[k] + uvw[0]*data[7].velocity[k] ) );
-		}
-	}
-	if (density_gradient) {
-		density_gradient[0] = muvw[1] * muvw[2] * ( data[0].density - data[1].density ) +
-		                       uvw[1] * muvw[2] * ( data[2].density - data[3].density ) +
-		                      muvw[1] *  uvw[2] * ( data[4].density - data[5].density ) +
-		                       uvw[1] *  uvw[2] * ( data[6].density - data[7].density );
-		
-		density_gradient[1] = muvw[2] * muvw[0] * ( data[0].density - data[2].density ) +
-		                       uvw[2] * muvw[0] * ( data[4].density - data[6].density ) +
-		                      muvw[2] *  uvw[0] * ( data[1].density - data[3].density ) +
-		                       uvw[2] *  uvw[0] * ( data[5].density - data[7].density );
-		
-		density_gradient[2] = muvw[2] * muvw[0] * ( data[0].density - data[4].density ) +
-		                       uvw[2] * muvw[0] * ( data[1].density - data[5].density ) +
-		                      muvw[2] *  uvw[0] * ( data[2].density - data[6].density ) +
-		                       uvw[2] *  uvw[0] * ( data[3].density - data[7].density );
-	}
-}
-
-static void hair_velocity_smoothing(const HairGridVert *hairgrid, const float gmin[3], const float scale[3], float smoothfac,
-                                    lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
-{
-	int v;
-	/* calculate forces */
-	for (v = 0; v < numverts; v++) {
-		float density, velocity[3];
-		
-		hair_grid_interpolate(hairgrid, hair_grid_res, gmin, scale, lX[v], &density, velocity, NULL);
-		
-		sub_v3_v3(velocity, lV[v]);
-		madd_v3_v3fl(lF[v], velocity, smoothfac);
-	}
-}
-
-static void hair_velocity_collision(const HairGridVert *collgrid, const float gmin[3], const float scale[3], float collfac,
-                                    lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
-{
-	int v;
-	/* calculate forces */
-	for (v = 0; v < numverts; v++) {
-		int offset = hair_grid_offset(lX[v], hair_grid_res, gmin, scale);
-		
-		if (collgrid[offset].density > 0.0f) {
-			lF[v][0] += collfac * (collgrid[offset].velocity[0] - lV[v][0]);
-			lF[v][1] += collfac * (collgrid[offset].velocity[1] - lV[v][1]);
-			lF[v][2] += collfac * (collgrid[offset].velocity[2] - lV[v][2]);
-		}
-	}
-}
-
-static void hair_pressure_force(const HairGridVert *hairgrid, const float gmin[3], const float scale[3], float pressurefac, float minpressure,
-                                lfVector *lF, lfVector *lX, unsigned int numverts)
-{
-	int v;
-	
-	/* calculate forces */
-	for (v = 0; v < numverts; v++) {
-		float density, gradient[3], gradlen;
-		
-		hair_grid_interpolate(hairgrid, hair_grid_res, gmin, scale, lX[v], &density, NULL, gradient);
-		
-		gradlen = normalize_v3(gradient) - minpressure;
-		if (gradlen < 0.0f)
-			continue;
-		mul_v3_fl(gradient, gradlen);
-		
-		madd_v3_v3fl(lF[v], gradient, pressurefac);
-	}
-}
-
-static void hair_volume_get_boundbox(lfVector *lX, unsigned int numverts, float gmin[3], float gmax[3])
-{
-	int i;
-	
-	INIT_MINMAX(gmin, gmax);
-	for (i = 0; i < numverts; i++)
-		DO_MINMAX(lX[i], gmin, gmax);
-}
-
-BLI_INLINE bool hair_grid_point_valid(const float vec[3], float gmin[3], float gmax[3])
-{
-	return !(vec[0] < gmin[0] || vec[1] < gmin[1] || vec[2] < gmin[2] ||
-	         vec[0] > gmax[0] || vec[1] > gmax[1] || vec[2] > gmax[2]);
-}
-
-BLI_INLINE float dist_tent_v3f3(const float a[3], float x, float y, float z)
-{
-	float w = (1.0f - fabsf(a[0] - x)) * (1.0f - fabsf(a[1] - y)) * (1.0f - fabsf(a[2] - z));
-	return w;
-}
-
-/* returns the grid array offset as well to avoid redundant calculation */
-static int hair_grid_weights(int res, const float gmin[3], const float scale[3], const float vec[3], float weights[8])
-{
-	int i, j, k, offset;
-	float uvw[3];
-	
-	i = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 0);
-	j = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 1);
-	k = HAIR_GRID_INDEX_AXIS(vec, res, gmin, scale, 2);
-	offset = i + (j + k*res)*res;
-	
-	uvw[0] = (vec[0] - gmin[0]) / scale[0];
-	uvw[1] = (vec[1] - gmin[1]) / scale[1];
-	uvw[2] = (vec[2] - gmin[2]) / scale[2];
-	
-	weights[0] = dist_tent_v3f3(uvw, (float)i    , (float)j    , (float)k    );
-	weights[1] = dist_tent_v3f3(uvw, (float)(i+1), (float)j    , (float)k    );
-	weights[2] = dist_tent_v3f3(uvw, (float)i    , (float)(j+1), (float)k    );
-	weights[3] = dist_tent_v3f3(uvw, (float)(i+1), (float)(j+1), (float)k    );
-	weights[4] = dist_tent_v3f3(uvw, (float)i    , (float)j    , (float)(k+1));
-	weights[5] = dist_tent_v3f3(uvw, (float)(i+1), (float)j    , (float)(k+1));
-	weights[6] = dist_tent_v3f3(uvw, (float)i    , (float)(j+1), (float)(k+1));
-	weights[7] = dist_tent_v3f3(uvw, (float)(i+1), (float)(j+1), (float)(k+1));
-	
-	return offset;
-}
-
-static HairGridVert *hair_volume_create_hair_grid(ClothModifierData *clmd, lfVector *lX, lfVector *lV, unsigned int numverts)
-{
-	int res = hair_grid_res;
-	int size = hair_grid_size(res);
-	HairGridVert *hairgrid;
-	float gmin[3], gmax[3], scale[3];
-	/* 2.0f is an experimental value that seems to give good results */
-	float smoothfac = 2.0f * clmd->sim_parms->velocity_smooth;
-	unsigned int	v = 0;
-	int	            i = 0;
-
-	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
-	hair_grid_get_scale(res, gmin, gmax, scale);
-
-	hairgrid = MEM_mallocN(sizeof(HairGridVert) * size, "hair voxel data");
-
-	/* initialize grid */
-	for (i = 0; i < size; ++i) {
-		zero_v3(hairgrid[i].velocity);
-		hairgrid[i].density = 0.0f;
-	}
-
-	/* gather velocities & density */
-	if (smoothfac > 0.0f) {
-		for (v = 0; v < numverts; v++) {
-			float *V = lV[v];
-			float weights[8];
-			int di, dj, dk;
-			int offset;
-			
-			if (!hair_grid_point_valid(lX[v], gmin, gmax))
-				continue;
-			
-			offset = hair_grid_weights(res, gmin, scale, lX[v], weights);
-			
-			for (di = 0; di < 2; ++di) {
-				for (dj = 0; dj < 2; ++dj) {
-					for (dk = 0; dk < 2; ++dk) {
-						int voffset = offset + di + (dj + dk*res)*res;
-						int iw = di + dj*2 + dk*4;
-						
-						hairgrid[voffset].density += weights[iw];
-						madd_v3_v3fl(hairgrid[voffset].velocity, V, weights[iw]);
-					}
-				}
-			}
-		}
-	}
-
-	/* divide velocity with density */
-	for (i = 0; i < size; i++) {
-		float density = hairgrid[i].density;
-		if (density > 0.0f)
-			mul_v3_fl(hairgrid[i].velocity, 1.0f/density);
-	}
-	
-	return hairgrid;
-}
-
-
-static HairGridVert *hair_volume_create_collision_grid(ClothModifierData *clmd, lfVector *lX, unsigned int numverts)
-{
-	int res = hair_grid_res;
-	int size = hair_grid_size(res);
-	HairGridVert *collgrid;
-	ListBase *colliders;
-	ColliderCache *col = NULL;
-	float gmin[3], gmax[3], scale[3];
-	/* 2.0f is an experimental value that seems to give good results */
-	float collfac = 2.0f * clmd->sim_parms->collider_friction;
-	unsigned int	v = 0;
-	int	            i = 0;
-
-	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
-	hair_grid_get_scale(res, gmin, gmax, scale);
-
-	collgrid = MEM_mallocN(sizeof(HairGridVert) * size, "hair collider voxel data");
-
-	/* initialize grid */
-	for (i = 0; i < size; ++i) {
-		zero_v3(collgrid[i].velocity);
-		collgrid[i].density = 0.0f;
-	}
-
-	/* gather colliders */
-	colliders = get_collider_cache(clmd->scene, NULL, NULL);
-	if (colliders && collfac > 0.0f) {
-		for (col = colliders->first; col; col = col->next) {
-			MVert *loc0 = col->collmd->x;
-			MVert *loc1 = col->collmd->xnew;
-			float vel[3];
-			float weights[8];
-			int di, dj, dk;
-			
-			for (v=0; v < col->collmd->numverts; v++, loc0++, loc1++) {
-				int offset;
-				
-				if (!hair_grid_point_valid(loc1->co, gmin, gmax))
-					continue;
-				
-				offset = hair_grid_weights(res, gmin, scale, lX[v], weights);
-				
-				sub_v3_v3v3(vel, loc1->co, loc0->co);
-				
-				for (di = 0; di < 2; ++di) {
-					for (dj = 0; dj < 2; ++dj) {
-						for (dk = 0; dk < 2; ++dk) {
-							int voffset = offset + di + (dj + dk*res)*res;
-							int iw = di + dj*2 + dk*4;
-							
-							collgrid[voffset].density += weights[iw];
-							madd_v3_v3fl(collgrid[voffset].velocity, vel, weights[iw]);
-						}
-					}
-				}
-			}
-		}
-	}
-	free_collider_cache(&colliders);
-
-	/* divide velocity with density */
-	for (i = 0; i < size; i++) {
-		float density = collgrid[i].density;
-		if (density > 0.0f)
-			mul_v3_fl(collgrid[i].velocity, 1.0f/density);
-	}
-	
-	return collgrid;
-}
-
-static void hair_volume_forces(ClothModifierData *clmd, lfVector *lF, lfVector *lX, lfVector *lV, unsigned int numverts)
-{
-	HairGridVert *hairgrid, *collgrid;
-	float gmin[3], gmax[3], scale[3];
-	/* 2.0f is an experimental value that seems to give good results */
-	float smoothfac = 2.0f * clmd->sim_parms->velocity_smooth;
-	float collfac = 2.0f * clmd->sim_parms->collider_friction;
-	float pressfac = clmd->sim_parms->pressure;
-	float minpress = clmd->sim_parms->pressure_threshold;
-	
-	if (smoothfac <= 0.0f && collfac <= 0.0f && pressfac <= 0.0f)
-		return;
-	
-	hair_volume_get_boundbox(lX, numverts, gmin, gmax);
-	hair_grid_get_scale(hair_grid_res, gmin, gmax, scale);
-	
-	hairgrid = hair_volume_create_hair_grid(clmd, lX, lV, numverts);
-	collgrid = hair_volume_create_collision_grid(clmd, lX, numverts);
-	
-	hair_velocity_smoothing(hairgrid, gmin, scale, smoothfac, lF, lX, lV, numverts);
-	hair_velocity_collision(collgrid, gmin, scale, collfac, lF, lX, lV, numverts);
-	hair_pressure_force(hairgrid, gmin, scale, pressfac, minpress, lF, lX, numverts);
-	
-	MEM_freeN(hairgrid);
-	MEM_freeN(collgrid);
-}
-
-bool implicit_hair_volume_get_texture_data(Object *UNUSED(ob), ClothModifierData *clmd, ListBase *UNUSED(effectors), VoxelData *vd)
-{
-	lfVector *lX, *lV;
-	HairGridVert *hairgrid/*, *collgrid*/;
-	int numverts;
-	int totres, i;
-	int depth;
-
-	if (!clmd->clothObject || !clmd->clothObject->implicit)
-		return false;
-
-	lX = clmd->clothObject->implicit->X;
-	lV = clmd->clothObject->implicit->V;
-	numverts = clmd->clothObject->numverts;
-
-	hairgrid = hair_volume_create_hair_grid(clmd, lX, lV, numverts);
-//	collgrid = hair_volume_create_collision_grid(clmd, lX, numverts);
-
-	vd->resol[0] = hair_grid_res;
-	vd->resol[1] = hair_grid_res;
-	vd->resol[2] = hair_grid_res;
-	
-	totres = hair_grid_size(hair_grid_res);
-	
-	if (vd->hair_type == TEX_VD_HAIRVELOCITY) {
-		depth = 4;
-		vd->data_type = TEX_VD_RGBA_PREMUL;
-	}
-	else {
-		depth = 1;
-		vd->data_type = TEX_VD_INTENSITY;
-	}
-	
-	if (totres > 0) {
-		vd->dataset = (float *)MEM_mapallocN(sizeof(float) * depth * (totres), "hair volume texture data");
-		
-		for (i = 0; i < totres; ++i) {
-			switch (vd->hair_type) {
-				case TEX_VD_HAIRDENSITY:
-					vd->dataset[i] = hairgrid[i].density;
-					break;
-				
-				case TEX_VD_HAIRRESTDENSITY:
-					vd->dataset[i] = 0.0f; // TODO
-					break;
-				
-				case TEX_VD_HAIRVELOCITY:
-					vd->dataset[i + 0*totres] = hairgrid[i].velocity[0];
-					vd->dataset[i + 1*totres] = hairgrid[i].velocity[1];
-					vd->dataset[i + 2*totres] = hairgrid[i].velocity[2];
-					vd->dataset[i + 3*totres] = len_v3(hairgrid[i].velocity);
-					break;
-				
-				case TEX_VD_HAIRENERGY:
-					vd->dataset[i] = 0.0f; // TODO
-					break;
-			}
-		}
-	}
-	else {
-		vd->dataset = NULL;
-	}
-	
-	MEM_freeN(hairgrid);
-//	MEM_freeN(collgrid);
-	
-	return true;
-}
-
-/* ================================ */
-
 static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), lfVector *lF, lfVector *lX, lfVector *lV, fmatrix3x3 *dFdV, fmatrix3x3 *dFdX, ListBase *effectors, float time, fmatrix3x3 *M)
 {
 	/* Collect forces and derivatives:  F, dFdX, dFdV */
@@ -2052,7 +1606,8 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), lfVec
 	zero_lfvector(lF, numverts);
 #endif
 
-	hair_volume_forces(clmd, lF, lX, lV, numverts);
+	// XXX TODO
+//	hair_volume_forces(clmd, lF, lX, lV, numverts);
 
 #ifdef CLOTH_FORCE_DRAG
 	/* set dFdX jacobi matrix diagonal entries to -spring_air */