=cloth collisions=

Plugged the eltopo library into the cloth solver.
I was playing with it earlier, and it's so easy to
use I decided to quickly put it in (trunk's) cloth.

See http://www.cs.ubc.ca/labs/imager/tr/2009/eltopo/eltopo.html
.  The authors are on the bleeding edge of continuous collision
detection (one of them did ILM's cloth sim).  
I
don't really have to time to plug it into softbody, particles,
bullet, fluid, etc, but doing so would be pretty straightforward.
I'll leave that up to someone else.

To use, turn on USE_ELTOPO (in cmake) or WITH_BF_ELTOPO in scons.

4 files changed, 709 insertions, 5 deletions

diff --git a/source/blender/blenkernel/BKE_collision.h b/source/blender/blenkernel/BKE_collision.h
index b54d4275719..7018a638831 100644
--- a/source/blender/blenkernel/BKE_collision.h
+++ b/source/blender/blenkernel/BKE_collision.h
@@ -63,7 +63,11 @@ struct LinkNode;
 /* COLLISION FLAGS */
 typedef enum
 {
-	COLLISION_IN_FUTURE = ( 1 << 1 ),
+	COLLISION_IN_FUTURE =		(1 << 1),
+#ifdef USE_ELTOPO
+	COLLISION_USE_COLLFACE =	(1 << 2),
+	COLLISION_IS_EDGES =		(1 << 3),
+#endif
 } COLLISION_FLAGS;
 
 
@@ -81,7 +85,13 @@ typedef struct CollPair
 	float pa[3], pb[3]; // collision point p1 on face1, p2 on face2
 	int flag;
 	float time; // collision time, from 0 up to 1
+#ifdef USE_ELTOPO /*either ap* or bp* can be set, but not both*/
+	float bary[3];
+	int ap1, ap2, ap3, collp, bp1, bp2, bp3;
+	int collface;
+#else
 	int ap1, ap2, ap3, bp1, bp2, bp3;
+#endif
 	int pointsb[4];
 }
 CollPair;
@@ -109,6 +119,7 @@ typedef struct FaceCollPair
 	float pa[3], pb[3]; // collision point p1 on face1, p2 on face2
 }
 FaceCollPair;
+
 ////////////////////////////////////////
 
 
diff --git a/source/blender/blenkernel/CMakeLists.txt b/source/blender/blenkernel/CMakeLists.txt
index aaa596862c5..0a2aaffa3d1 100644
--- a/source/blender/blenkernel/CMakeLists.txt
+++ b/source/blender/blenkernel/CMakeLists.txt
@@ -140,7 +140,7 @@ set(SRC
 	intern/writeavi.c
 	intern/writeffmpeg.c
 	intern/writeframeserver.c
-
+	
 	BKE_DerivedMesh.h
 	BKE_action.h
 	BKE_anim.h
@@ -235,6 +235,11 @@ if(WITH_BULLET)
 	add_definitions(-DUSE_BULLET)
 endif()
 
+if(WITH_ELTOPO)
+	list(APPEND INC ../../../extern/eltopo)
+	add_definitions(-DUSE_ELTOPO)
+endif()
+
 if(WITH_IMAGE_OPENEXR)
 	add_definitions(-DWITH_OPENEXR)
 endif()
diff --git a/source/blender/blenkernel/SConscript b/source/blender/blenkernel/SConscript
index bef72d3bf67..66011c4f396 100644
--- a/source/blender/blenkernel/SConscript
+++ b/source/blender/blenkernel/SConscript
@@ -27,6 +27,10 @@ if env['WITH_BF_PYTHON']:
     if env['BF_DEBUG']:
         defs.append('DEBUG')
 
+if env['WITH_BF_ELTOPO']:
+    incs += ' ../../../extern/eltopo'
+    defs.append('USE_ELTOPO')
+        
 if env['WITH_BF_QUICKTIME']:
     incs += ' ../quicktime'
 
diff --git a/source/blender/blenkernel/intern/collision.c b/source/blender/blenkernel/intern/collision.c
index 88b6ca296c7..a5f07f56d36 100644
--- a/source/blender/blenkernel/intern/collision.c
+++ b/source/blender/blenkernel/intern/collision.c
@@ -48,6 +48,8 @@
 #include "BLI_math.h"
 #include "BLI_edgehash.h"
 #include "BLI_utildefines.h"
+#include "BLI_ghash.h"
+#include "BLI_memarena.h"
 
 #include "BKE_DerivedMesh.h"
 #include "BKE_global.h"
@@ -63,6 +65,10 @@
 #include "BLI_kdopbvh.h"
 #include "BKE_collision.h"
 
+#ifdef USE_ELTOPO
+#include "eltopo-capi.h"
+#endif
+
 
 /***********************************
 Collision modifier code start
@@ -486,7 +492,7 @@ DO_INLINE void collision_interpolateOnTriangle ( float to[3], float v1[3], float
 	VECADDMUL ( to, v3, w3 );
 }
 
-
+#ifndef USE_ELTOPO
 static int cloth_collision_response_static ( ClothModifierData *clmd, CollisionModifierData *collmd, CollPair *collpair, CollPair *collision_end )
 {
 	int result = 0;
@@ -601,6 +607,662 @@ static int cloth_collision_response_static ( ClothModifierData *clmd, CollisionM
 	}
 	return result;
 }
+#endif
+
+#ifdef USE_ELTOPO
+typedef struct edgepairkey {
+	int a1, a2, b1, b2;
+} edgepairkey;
+
+unsigned int edgepair_hash(void *vkey)
+{
+	edgepairkey *key = vkey;
+	int keys[4] = {key->a1, key->a2, key->b1, key->b2};
+	int i, j;
+	
+	for (i=0; i<4; i++) {
+		for (j=0; j<3; j++) {
+			if (keys[j] >= keys[j+1]) {
+				SWAP(int, keys[j], keys[j+1]);
+			}
+		}
+	}
+	
+	return keys[0]*101 + keys[1]*72 + keys[2]*53 + keys[3]*34;
+}
+
+int edgepair_cmp(const void *va, const void *vb)
+{
+	edgepairkey *a = va, *b = vb;
+	int keysa[4] = {a->a1, a->a2, a->b1, a->b2};
+	int keysb[4] = {b->a1, b->a2, b->b1, b->b2};
+	int i;
+	
+	for (i=0; i<4; i++) {
+		int j, ok=0;
+		for (j=0; j<4; j++) {
+			if (keysa[i] == keysa[j]) {
+				ok = 1;
+				break;
+			}
+		}
+		if (!ok)
+			return -1;
+	}
+	
+	return 0;
+}
+
+static void get_edgepairkey(edgepairkey *key, int a1, int a2, int b1, int b2)
+{
+	key->a1 = a1;
+	key->a2 = a2;
+	key->b1 = b1;
+	key->b2 = b2;
+}
+
+/*an immense amount of duplication goes on here. . .a major performance hit, I'm sure*/
+static CollPair* cloth_edge_collision ( ModifierData *md1, ModifierData *md2, 
+										BVHTreeOverlap *overlap, CollPair *collpair,
+										GHash *visithash, MemArena *arena)
+{
+	ClothModifierData *clmd = ( ClothModifierData * ) md1;
+	CollisionModifierData *collmd = ( CollisionModifierData * ) md2;
+	MFace *face1=NULL, *face2 = NULL;
+	ClothVertex *verts1 = clmd->clothObject->verts;
+	double distance = 0;
+	edgepairkey *key, tstkey;
+	float epsilon1 = clmd->coll_parms->epsilon;
+	float epsilon2 = BLI_bvhtree_getepsilon ( collmd->bvhtree );
+	float no[3], uv[3], t, relnor;
+	int i, i1, i2, i3, i4, i5, i6;
+	Cloth *cloth = clmd->clothObject;
+	float n1[3], n2[3], off[3], v1[2][3], v2[2][3], v3[2][3], v4[2][3], v5[2][3], v6[2][3];
+	void **verts[] = {v1, v2, v3, v4, v5, v6};
+	int j, ret, bp1, bp2, bp3, ap1, ap2, ap3, table[6];
+	
+	face1 = & ( clmd->clothObject->mfaces[overlap->indexA] );
+	face2 = & ( collmd->mfaces[overlap->indexB] );
+
+	// check all 4 possible collisions
+	for ( i = 0; i < 4; i++ )
+	{
+		if ( i == 0 )
+		{
+			// fill faceA
+			ap1 = face1->v1;
+			ap2 = face1->v2;
+			ap3 = face1->v3;
+
+			// fill faceB
+			bp1 = face2->v1;
+			bp2 = face2->v2;
+			bp3 = face2->v3;
+		}
+		else if ( i == 1 )
+		{
+			if ( face1->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v3;
+				ap3 = face1->v4;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v2;
+				bp3 = face2->v3;
+			}
+			else {
+				continue;
+			}
+		}
+		if ( i == 2 )
+		{
+			if ( face2->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v2;
+				ap3 = face1->v3;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v3;
+				bp3 = face2->v4;
+			}
+			else {
+				continue;
+			}
+		}
+		else if ( i == 3 )
+		{
+			if ( face1->v4 && face2->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v3;
+				ap3 = face1->v4;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v3;
+				bp3 = face2->v4;
+			}
+			else {
+				continue;
+			}
+		}
+		
+		copy_v3_v3(v1[0], cloth->verts[ap1].txold); 
+		copy_v3_v3(v1[1], cloth->verts[ap1].tx);
+		copy_v3_v3(v2[0], cloth->verts[ap2].txold);
+		copy_v3_v3(v2[1], cloth->verts[ap2].tx);
+		copy_v3_v3(v3[0], cloth->verts[ap3].txold);
+		copy_v3_v3(v3[1], cloth->verts[ap3].tx);
+		
+		copy_v3_v3(v4[0], collmd->current_x[bp1].co);
+		copy_v3_v3(v4[1], collmd->current_xnew[bp1].co);
+		copy_v3_v3(v5[0], collmd->current_x[bp2].co);
+		copy_v3_v3(v5[1], collmd->current_xnew[bp2].co);
+		copy_v3_v3(v6[0], collmd->current_x[bp3].co);
+		copy_v3_v3(v6[1], collmd->current_xnew[bp3].co);
+		
+		normal_tri_v3(n2, v4[1], v5[1], v6[1]);
+
+		/*offset new positions a bit, to account for margins*/
+		copy_v3_v3(off, n2);
+		mul_v3_fl(off,  epsilon1 + epsilon2 + ALMOST_ZERO);
+		add_v3_v3(v4[1], off); add_v3_v3(v5[1], off); add_v3_v3(v6[1], off);
+		
+		i1 = ap1; i2 = ap2; i3 = ap3;
+		i4 = bp1; i5 = bp2; i6 = bp3;
+
+		for (j=0; j<3; j++) {
+			int collp1, collp2, k, j2 = (j+1)%3;
+			
+			table[0] = ap1; table[1] = ap2; table[2] = ap3;
+			table[3] = bp1; table[4] = bp2; table[5] = bp3;
+			for (k=0; k<3; k++) {
+				int k2 = (k+1)%3;
+				
+				get_edgepairkey(&tstkey, table[j], table[j2], table[k+3], table[k2+3]);
+				if (BLI_ghash_haskey(visithash, &tstkey))
+					continue;
+				
+				key = BLI_memarena_alloc(arena, sizeof(edgepairkey));
+				*key = tstkey;
+				BLI_ghash_insert(visithash, key, NULL);
+
+				ret = eltopo_line_line_moving_isect_v3v3_f(verts[j], table[j], verts[j2], table[j2], 
+														   verts[k+3], table[k+3], verts[k2+3], table[k2+3], 
+														   no, uv, &t, &relnor);
+				
+				/*cloth vert versus coll face*/
+				if (ret && dot_v3v3(n2, no) > 0.0) {
+					collpair->ap1 = table[j]; collpair->ap2 = table[j2]; 
+					collpair->bp1 = table[k+3]; collpair->bp2 = table[k2+3];
+					
+					copy_v3_v3(collpair->normal, no);
+					mul_v3_v3fl(collpair->vector, collpair->normal, relnor);
+					collpair->distance = relnor;
+					collpair->time = t;
+					
+					copy_v2_v2(collpair->bary, uv);
+					
+					collpair->flag = COLLISION_IS_EDGES;
+					collpair++;
+				}
+			}
+		}
+	}
+	
+	return collpair;
+}
+
+static int cloth_edge_collision_response_moving ( ClothModifierData *clmd, CollisionModifierData *collmd, CollPair *collpair, CollPair *collision_end )
+{
+	int result = 0;
+	Cloth *cloth1;
+	float w1, w2;
+	float v1[3], v2[3], relativeVelocity[3];
+	float magrelVel, pimpulse[3];
+
+	cloth1 = clmd->clothObject;
+
+	for ( ; collpair != collision_end; collpair++ )
+	{
+		if (!(collpair->flag & COLLISION_IS_EDGES))
+			continue;
+		
+		// was: txold
+		w1 = collpair->bary[0]; w2 = collpair->bary[1];			
+		
+		// Calculate relative "velocity".
+		VECADDFAC(v1, cloth1->verts[collpair->ap1].tv, cloth1->verts[collpair->ap2].tv, w1);
+		VECADDFAC(v2, collmd->current_v[collpair->bp1].co, collmd->current_v[collpair->bp2].co, w2);
+		
+		VECSUB ( relativeVelocity, v2, v1);
+		
+		// Calculate the normal component of the relative velocity (actually only the magnitude - the direction is stored in 'normal').
+		magrelVel = INPR ( relativeVelocity, collpair->normal );
+
+		// If v_n_mag < 0 the edges are approaching each other.
+		if ( magrelVel > ALMOST_ZERO )
+		{
+			// Calculate Impulse magnitude to stop all motion in normal direction.
+			float magtangent = 0, repulse = 0, d = 0;
+			double impulse = 0.0;
+			float vrel_t_pre[3];
+			float temp[3], spf;
+			
+			zero_v3(pimpulse);
+			
+			// calculate tangential velocity
+			VECCOPY ( temp, collpair->normal );
+			mul_v3_fl( temp, magrelVel );
+			VECSUB ( vrel_t_pre, relativeVelocity, temp );
+
+			// Decrease in magnitude of relative tangential velocity due to coulomb friction
+			// in original formula "magrelVel" should be the "change of relative velocity in normal direction"
+			magtangent = MIN2 ( clmd->coll_parms->friction * 0.01 * magrelVel,sqrt ( INPR ( vrel_t_pre,vrel_t_pre ) ) );
+
+			// Apply friction impulse.
+			if ( magtangent > ALMOST_ZERO )
+			{
+				normalize_v3( vrel_t_pre );
+
+				impulse = magtangent; // 2.0 * 
+				VECADDMUL ( pimpulse, vrel_t_pre, impulse);
+			}
+
+			// Apply velocity stopping impulse
+			// I_c = m * v_N / 2.0
+			// no 2.0 * magrelVel normally, but looks nicer DG
+			impulse =  magrelVel;
+
+			VECADDMUL ( pimpulse, collpair->normal, impulse);
+
+			// Apply repulse impulse if distance too short
+			// I_r = -min(dt*kd, m(0,1d/dt - v_n))
+			spf = (float)clmd->sim_parms->stepsPerFrame / clmd->sim_parms->timescale;
+
+			d = collpair->distance;
+			if ( ( magrelVel < 0.1*d*spf ) && ( d > ALMOST_ZERO ) )
+			{
+				repulse = MIN2 ( d*1.0/spf, 0.1*d*spf - magrelVel );
+
+				// stay on the safe side and clamp repulse
+				if ( impulse > ALMOST_ZERO )
+					repulse = MIN2 ( repulse, 5.0*impulse );
+				repulse = MAX2 ( impulse, repulse );
+
+				impulse = repulse / ( 5.0 ); // original 2.0 / 0.25
+				VECADDMUL ( pimpulse, collpair->normal, impulse);
+			}
+			
+			w2 = 1.0f-w1;
+			if (w1 < 0.5)
+				w1 *= 2.0;
+			else
+				w2 *= 2.0;
+			
+			
+			VECADDFAC(cloth1->verts[collpair->ap1].impulse, cloth1->verts[collpair->ap1].impulse, pimpulse, w1*2.0);
+			VECADDFAC(cloth1->verts[collpair->ap2].impulse, cloth1->verts[collpair->ap2].impulse, pimpulse, w2*2.0);
+			
+			cloth1->verts[collpair->ap1].impulse_count++;
+			cloth1->verts[collpair->ap2].impulse_count++;
+			
+			result = 1;
+		}
+	} 
+	
+	return result;
+}
+
+static int cloth_collision_response_moving ( ClothModifierData *clmd, CollisionModifierData *collmd, CollPair *collpair, CollPair *collision_end )
+{
+	int result = 0;
+	Cloth *cloth1;
+	float w1, w2, w3, u1, u2, u3;
+	float v1[3], v2[3], relativeVelocity[3];
+	float magrelVel;
+	float epsilon2 = BLI_bvhtree_getepsilon ( collmd->bvhtree );
+	
+	cloth1 = clmd->clothObject;
+
+	for ( ; collpair != collision_end; collpair++ )
+	{
+		if (collpair->flag & COLLISION_IS_EDGES)
+			continue;
+		
+		if ( collpair->flag & COLLISION_USE_COLLFACE ) {
+			// was: txold
+			w1 = collpair->bary[0]; w2 = collpair->bary[1]; w3 = collpair->bary[2];			
+
+			// Calculate relative "velocity".
+			collision_interpolateOnTriangle ( v1, collmd->current_v[collpair->bp1].co, collmd->current_v[collpair->bp2].co, collmd->current_v[collpair->bp3].co, w1, w2, w3);
+			
+			VECSUB ( relativeVelocity, v1, cloth1->verts[collpair->collp].tv);
+			
+			// Calculate the normal component of the relative velocity (actually only the magnitude - the direction is stored in 'normal').
+			magrelVel = INPR ( relativeVelocity, collpair->normal );
+	
+			// If v_n_mag < 0 the edges are approaching each other.
+			if ( magrelVel > ALMOST_ZERO )
+			{
+				// Calculate Impulse magnitude to stop all motion in normal direction.
+				float magtangent = 0, repulse = 0, d = 0;
+				double impulse = 0.0;
+				float vrel_t_pre[3];
+				float temp[3], spf;
+	
+				// calculate tangential velocity
+				VECCOPY ( temp, collpair->normal );
+				mul_v3_fl( temp, magrelVel );
+				VECSUB ( vrel_t_pre, relativeVelocity, temp );
+	
+				// Decrease in magnitude of relative tangential velocity due to coulomb friction
+				// in original formula "magrelVel" should be the "change of relative velocity in normal direction"
+				magtangent = MIN2 ( clmd->coll_parms->friction * 0.01 * magrelVel,sqrt ( INPR ( vrel_t_pre,vrel_t_pre ) ) );
+	
+				// Apply friction impulse.
+				if ( magtangent > ALMOST_ZERO )
+				{
+					normalize_v3( vrel_t_pre );
+	
+					impulse = magtangent; // 2.0 * 
+					VECADDMUL ( cloth1->verts[collpair->collp].impulse, vrel_t_pre, impulse);
+				}
+	
+				// Apply velocity stopping impulse
+				// I_c = m * v_N / 2.0
+				// no 2.0 * magrelVel normally, but looks nicer DG
+				impulse =  magrelVel/2.0;
+	
+				VECADDMUL ( cloth1->verts[collpair->collp].impulse, collpair->normal, impulse);
+				cloth1->verts[collpair->collp].impulse_count++;
+	
+				// Apply repulse impulse if distance too short
+				// I_r = -min(dt*kd, m(0,1d/dt - v_n))
+				spf = (float)clmd->sim_parms->stepsPerFrame / clmd->sim_parms->timescale;
+	
+				d = -collpair->distance;
+				if ( ( magrelVel < 0.1*d*spf ) && ( d > ALMOST_ZERO ) )
+				{
+					repulse = MIN2 ( d*1.0/spf, 0.1*d*spf - magrelVel );
+	
+					// stay on the safe side and clamp repulse
+					if ( impulse > ALMOST_ZERO )
+						repulse = MIN2 ( repulse, 5.0*impulse );
+					repulse = MAX2 ( impulse, repulse );
+	
+					impulse = repulse / ( 5.0 ); // original 2.0 / 0.25
+					VECADDMUL ( cloth1->verts[collpair->collp].impulse, collpair->normal, impulse);
+				}
+	
+				result = 1;
+			}
+		} else {	
+			w1 = collpair->bary[0]; w2 = collpair->bary[1]; w3 = collpair->bary[2];			
+
+			// Calculate relative "velocity".
+			collision_interpolateOnTriangle ( v1, cloth1->verts[collpair->ap1].tv, cloth1->verts[collpair->ap2].tv, cloth1->verts[collpair->ap3].tv, w1, w2, w3 );
+	
+			VECSUB ( relativeVelocity, collmd->current_v[collpair->collp].co, v1);
+			
+			// Calculate the normal component of the relative velocity (actually only the magnitude - the direction is stored in 'normal').
+			magrelVel = INPR ( relativeVelocity, collpair->normal );
+	
+			// If v_n_mag < 0 the edges are approaching each other.
+			if ( magrelVel > ALMOST_ZERO )
+			{
+				// Calculate Impulse magnitude to stop all motion in normal direction.
+				float magtangent = 0, repulse = 0, d = 0;
+				double impulse = 0.0;
+				float vrel_t_pre[3], pimpulse[3] = {0.0f, 0.0f, 0.0f};
+				float temp[3], spf;
+	
+				// calculate tangential velocity
+				VECCOPY ( temp, collpair->normal );
+				mul_v3_fl( temp, magrelVel );
+				VECSUB ( vrel_t_pre, relativeVelocity, temp );
+	
+				// Decrease in magnitude of relative tangential velocity due to coulomb friction
+				// in original formula "magrelVel" should be the "change of relative velocity in normal direction"
+				magtangent = MIN2 ( clmd->coll_parms->friction * 0.01 * magrelVel,sqrt ( INPR ( vrel_t_pre,vrel_t_pre ) ) );
+	
+				// Apply friction impulse.
+				if ( magtangent > ALMOST_ZERO )
+				{
+					normalize_v3( vrel_t_pre );
+	
+					impulse = magtangent; // 2.0 * 
+					VECADDMUL ( pimpulse, vrel_t_pre, impulse);
+				}
+	
+				// Apply velocity stopping impulse
+				// I_c = m * v_N / 2.0
+				// no 2.0 * magrelVel normally, but looks nicer DG
+				impulse =  magrelVel/2.0;
+	
+				VECADDMUL ( pimpulse, collpair->normal, impulse);
+	
+				// Apply repulse impulse if distance too short
+				// I_r = -min(dt*kd, m(0,1d/dt - v_n))
+				spf = (float)clmd->sim_parms->stepsPerFrame / clmd->sim_parms->timescale;
+	
+				d = -collpair->distance;
+				if ( ( magrelVel < 0.1*d*spf ) && ( d > ALMOST_ZERO ) )
+				{
+					repulse = MIN2 ( d*1.0/spf, 0.1*d*spf - magrelVel );
+	
+					// stay on the safe side and clamp repulse
+					if ( impulse > ALMOST_ZERO )
+						repulse = MIN2 ( repulse, 5.0*impulse );
+					repulse = MAX2 ( impulse, repulse );
+	
+					impulse = repulse / ( 2.0 ); // original 2.0 / 0.25
+					VECADDMUL ( pimpulse, collpair->normal, impulse);
+				}
+				
+				if (w1 < 0.5) w1 *= 2.0;
+				if (w2 < 0.5) w2 *= 2.0;
+				if (w3 < 0.5) w3 *= 2.0;
+				
+				VECADDMUL(cloth1->verts[collpair->ap1].impulse, pimpulse, w1*2.0);
+				VECADDMUL(cloth1->verts[collpair->ap2].impulse, pimpulse, w2*2.0);
+				VECADDMUL(cloth1->verts[collpair->ap3].impulse, pimpulse, w3*2.0);;
+				cloth1->verts[collpair->ap1].impulse_count++;
+				cloth1->verts[collpair->ap2].impulse_count++;
+				cloth1->verts[collpair->ap3].impulse_count++;
+				
+				result = 1;
+			}
+		}
+	} 
+	
+	return result;
+}
+
+static CollPair* cloth_collision ( ModifierData *md1, ModifierData *md2, BVHTreeOverlap *overlap, 
+								   CollPair *collpair)
+{
+	ClothModifierData *clmd = ( ClothModifierData * ) md1;
+	CollisionModifierData *collmd = ( CollisionModifierData * ) md2;
+	MFace *face1=NULL, *face2 = NULL;
+	ClothVertex *verts1 = clmd->clothObject->verts;
+	double distance = 0;
+	float epsilon1 = clmd->coll_parms->epsilon;
+	float epsilon2 = BLI_bvhtree_getepsilon ( collmd->bvhtree );
+	float no[3], uv[3], t, relnor;
+	int i, i1, i2, i3, i4, i5, i6;
+	Cloth *cloth = clmd->clothObject;
+	float n1[3], n2[3], off[3], v1[2][3], v2[2][3], v3[2][3], v4[2][3], v5[2][3], v6[2][3];
+	int j, ret, bp1, bp2, bp3, ap1, ap2, ap3;
+	
+	face1 = & ( clmd->clothObject->mfaces[overlap->indexA] );
+	face2 = & ( collmd->mfaces[overlap->indexB] );
+
+	// check all 4 possible collisions
+	for ( i = 0; i < 4; i++ )
+	{
+		if ( i == 0 )
+		{
+			// fill faceA
+			ap1 = face1->v1;
+			ap2 = face1->v2;
+			ap3 = face1->v3;
+
+			// fill faceB
+			bp1 = face2->v1;
+			bp2 = face2->v2;
+			bp3 = face2->v3;
+		}
+		else if ( i == 1 )
+		{
+			if ( face1->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v3;
+				ap3 = face1->v4;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v2;
+				bp3 = face2->v3;
+			}
+			else {
+				continue;
+			}
+		}
+		if ( i == 2 )
+		{
+			if ( face2->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v2;
+				ap3 = face1->v3;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v3;
+				bp3 = face2->v4;
+			}
+			else {
+				continue;
+			}
+		}
+		else if ( i == 3 )
+		{
+			if ( face1->v4 && face2->v4 )
+			{
+				// fill faceA
+				ap1 = face1->v1;
+				ap2 = face1->v3;
+				ap3 = face1->v4;
+
+				// fill faceB
+				bp1 = face2->v1;
+				bp2 = face2->v3;
+				bp3 = face2->v4;
+			}
+			else {
+				continue;
+			}
+		}
+		
+		copy_v3_v3(v1[0], cloth->verts[ap1].txold); 
+		copy_v3_v3(v1[1], cloth->verts[ap1].tx);
+		copy_v3_v3(v2[0], cloth->verts[ap2].txold);
+		copy_v3_v3(v2[1], cloth->verts[ap2].tx);
+		copy_v3_v3(v3[0], cloth->verts[ap3].txold);
+		copy_v3_v3(v3[1], cloth->verts[ap3].tx);
+		
+		copy_v3_v3(v4[0], collmd->current_x[bp1].co);
+		copy_v3_v3(v4[1], collmd->current_xnew[bp1].co);
+		copy_v3_v3(v5[0], collmd->current_x[bp2].co);
+		copy_v3_v3(v5[1], collmd->current_xnew[bp2].co);
+		copy_v3_v3(v6[0], collmd->current_x[bp3].co);
+		copy_v3_v3(v6[1], collmd->current_xnew[bp3].co);
+		
+		normal_tri_v3(n2, v4[1], v5[1], v6[1]);
+
+		/*offset new positions a bit, to account for margins*/
+		copy_v3_v3(off, n2);
+		mul_v3_fl(off,  epsilon1 + epsilon2 + ALMOST_ZERO);
+		add_v3_v3(v4[1], off); add_v3_v3(v5[1], off); add_v3_v3(v6[1], off);
+		
+		i1 = ap1; i2 = ap2; i3 = ap3;
+		i4 = bp1; i5 = bp2; i6 = bp3;
+		
+		for (j=0; j<6; j++) {
+			int collp;
+
+			switch (j) {
+			case 0:
+				ret = eltopo_point_tri_moving_v3v3_f(v1, i1, v4, i4, v5, i5, v6, i6, no, uv, &t, &relnor);
+				collp = ap1;
+				break;
+			case 1:
+				collp = ap2;
+				ret = eltopo_point_tri_moving_v3v3_f(v2, i2, v4, i4, v5, i5, v6, i6, no, uv, &t, &relnor);
+				break;
+			case 2:
+				collp = ap3;
+				ret = eltopo_point_tri_moving_v3v3_f(v3, i3, v4, i4, v5, i5, v6, i6, no, uv, &t, &relnor);
+				break;
+			case 3:
+				collp = bp1;
+				ret = eltopo_point_tri_moving_v3v3_f(v4, i4, v1, i1, v2, i2, v3, i3, no, uv, &t, &relnor);
+				break;
+			case 4:
+				collp = bp2;				
+				ret = eltopo_point_tri_moving_v3v3_f(v5, i5, v1, i1, v2, i2, v3, i3, no, uv, &t, &relnor);
+				break;
+			case 5:
+				collp = bp3;
+				ret = eltopo_point_tri_moving_v3v3_f(v6, i6, v1, i1, v2, i2, v3, i3, no, uv, &t, &relnor);
+				break;
+			}
+			
+			/*cloth vert versus coll face*/
+			if (ret && j < 3) {
+				collpair->bp1 = bp1; collpair->bp2 = bp2; collpair->bp3 = bp3;
+				collpair->collp = collp;
+				
+				copy_v3_v3(collpair->normal, no);
+				mul_v3_v3fl(collpair->vector, collpair->normal, relnor);
+				collpair->distance = relnor;
+				collpair->time = t;
+				
+				copy_v3_v3(collpair->bary, uv);
+				
+				collpair->flag = COLLISION_USE_COLLFACE;
+				collpair++;
+			} else if (ret && j >= 3) { /*coll vert versus cloth face*/
+				collpair->ap1 = ap1; collpair->ap2 = ap2; collpair->ap3 = ap3;
+				collpair->collp = collp;
+				
+				copy_v3_v3(collpair->normal, no);
+				mul_v3_v3fl(collpair->vector, collpair->normal, relnor);
+				collpair->distance = relnor;
+				collpair->time = t;
+				
+				copy_v3_v3(collpair->bary, uv);
+
+				collpair->flag = 0;
+				collpair++;
+			}
+		}
+	}
+	
+	return collpair;
+}
+#else
 
 //Determines collisions on overlap, collisions are written to collpair[i] and collision+number_collision_found is returned
 static CollPair* cloth_collision ( ModifierData *md1, ModifierData *md2, BVHTreeOverlap *overlap, CollPair *collpair )
@@ -741,6 +1403,8 @@ static CollPair* cloth_collision ( ModifierData *md1, ModifierData *md2, BVHTree
 	}
 	return collpair;
 }
+#endif
+
 
 #if 0
 static int cloth_collision_response_moving( ClothModifierData *clmd, CollisionModifierData *collmd, CollPair *collpair, CollPair *collision_end )
@@ -1446,17 +2110,32 @@ void free_collider_cache(ListBase **colliders)
 	}
 }
 
+
 static void cloth_bvh_objcollisions_nearcheck ( ClothModifierData * clmd, CollisionModifierData *collmd, CollPair **collisions, CollPair **collisions_index, int numresult, BVHTreeOverlap *overlap)
 {
 	int i;
+#ifdef USE_ELTOPO
+	GHash *visithash = BLI_ghash_new(edgepair_hash, edgepair_cmp, "visthash, collision.c");
+	MemArena *arena = BLI_memarena_new(1<<16, "edge hash arena, collision.c");
+#endif
 	
-	*collisions = ( CollPair* ) MEM_mallocN ( sizeof ( CollPair ) * numresult * 4, "collision array" ); //*4 since cloth_collision_static can return more than 1 collision
+	*collisions = ( CollPair* ) MEM_mallocN ( sizeof ( CollPair ) * numresult * 64, "collision array" ); //*4 since cloth_collision_static can return more than 1 collision
 	*collisions_index = *collisions;
 
 	for ( i = 0; i < numresult; i++ )
 	{
 		*collisions_index = cloth_collision ( ( ModifierData * ) clmd, ( ModifierData * ) collmd, overlap+i, *collisions_index );
 	}
+
+#ifdef USE_ELTOPO
+	for ( i = 0; i < numresult; i++ )
+	{
+		*collisions_index = cloth_edge_collision ( ( ModifierData * ) clmd, ( ModifierData * ) collmd,
+												   overlap+i, *collisions_index, visithash, arena );
+	}
+	BLI_ghash_free(visithash, NULL, NULL);
+	BLI_memarena_free(arena);
+#endif	
 }
 
 static int cloth_bvh_objcollisions_resolve ( ClothModifierData * clmd, CollisionModifierData *collmd, CollPair *collisions, CollPair *collisions_index)
@@ -1481,8 +2160,12 @@ static int cloth_bvh_objcollisions_resolve ( ClothModifierData * clmd, Collision
 
 		if ( collmd->bvhtree )
 		{
+#ifdef USE_ELTOPO
+			result += cloth_collision_response_moving(clmd, collmd, collisions, collisions_index);
+			result += cloth_edge_collision_response_moving(clmd, collmd, collisions, collisions_index);
+#else
 			result += cloth_collision_response_static ( clmd, collmd, collisions, collisions_index );
-
+#endif
 			// apply impulses in parallel
 			if ( result )
 			{
@@ -1557,6 +2240,7 @@ int cloth_bvh_objcollision (Object *ob, ClothModifierData * clmd, float step, fl
 				continue;
 			
 			/* move object to position (step) in time */
+			
 			collision_move_object ( collmd, step + dt, step );
 			
 			/* search for overlapping collision pairs */