[Bf-blender-cvs] [4599123] hair_immediate_fixes: Fixed implementation of the Conjugate Gradient method for the cloth solver that properly supports constraints with some degrees-of-freedom.
Lukas Tönne
noreply at git.blender.org
Wed Sep 3 23:55:06 CEST 2014
Commit: 4599123f8fced27c1e2e57cbe0398d9f91b6f2c1
Author: Lukas Tönne
Date: Wed Sep 3 23:49:24 2014 +0200
Branches: hair_immediate_fixes
https://developer.blender.org/rB4599123f8fced27c1e2e57cbe0398d9f91b6f2c1
Fixed implementation of the Conjugate Gradient method for the cloth
solver that properly supports constraints with some degrees-of-freedom.
The previous solver implementation only used the S matrix (constraint
filter matrix) for pinning vertices, in which case all elements are
zero and the error doesn't show up. With partial constraints (useful for
collision contacts) the matrix has non-zero off-diagonal elements and
the algorithm easily diverges.
There are also initial steps for implementing collision prevention as
described in the Baraff/Witkin paper "Large Steps in Cloth Simulation"
(http://www.cs.cmu.edu/~baraff/papers/sig98.pdf).
===================================================================
M source/blender/blenkernel/intern/collision.c
M source/blender/blenkernel/intern/implicit.c
===================================================================
diff --git a/source/blender/blenkernel/intern/collision.c b/source/blender/blenkernel/intern/collision.c
index 9b7da7e..abffdce 100644
--- a/source/blender/blenkernel/intern/collision.c
+++ b/source/blender/blenkernel/intern/collision.c
@@ -1133,9 +1133,6 @@ static CollPair *cloth_point_collpair(float p1[3], float p2[3], MVert *mverts, i
float facenor[3], v1p1[3], v1p2[3];
float w[3];
-// if (!isect_line_tri_v3(p1, p2, co1, co2, co3, &lambda, uv))
-// return collpair;
-
if (!cloth_point_face_collision_params(p1, p2, co1, co2, co3, facenor, &lambda, uv))
return collpair;
@@ -1159,7 +1156,7 @@ static CollPair *cloth_point_collpair(float p1[3], float p2[3], MVert *mverts, i
*/
copy_v3_v3(collpair->pa, p2);
collpair->distance = distance2;
- mul_v3_v3fl(collpair->vector, facenor, distance2);
+ mul_v3_v3fl(collpair->vector, facenor, -distance2);
w[0] = 1.0f - uv[0] - uv[1];
w[1] = uv[0];
diff --git a/source/blender/blenkernel/intern/implicit.c b/source/blender/blenkernel/intern/implicit.c
index 3240eb8..f77574c 100644
--- a/source/blender/blenkernel/intern/implicit.c
+++ b/source/blender/blenkernel/intern/implicit.c
@@ -347,6 +347,15 @@ static void print_fmatrix(float m3[3][3])
printf("%f\t%f\t%f\n", m3[1][0], m3[1][1], m3[1][2]);
printf("%f\t%f\t%f\n\n", m3[2][0], m3[2][1], m3[2][2]);
}
+
+static void print_sparse_matrix(fmatrix3x3 *m)
+{
+ if (m) {
+ unsigned int i;
+ for (i = 0; i < m[0].vcount + m[0].scount; i++)
+ print_fmatrix(m[i].m);
+ }
+}
#endif
/* copy 3x3 matrix */
@@ -907,10 +916,11 @@ DO_INLINE void filter(lfVector *V, fmatrix3x3 *S)
unsigned int i=0;
for (i = 0; i < S[0].vcount; i++) {
- mul_fvector_fmatrix(V[S[i].r], V[S[i].r], S[i].m);
+ mul_m3_v3(S[i].m, V[S[i].r]);
}
}
+#if 0
static int cg_filtered(lfVector *ldV, fmatrix3x3 *lA, lfVector *lB, lfVector *z, fmatrix3x3 *S)
{
// Solves for unknown X in equation AX=B
@@ -975,6 +985,73 @@ static int cg_filtered(lfVector *ldV, fmatrix3x3 *lA, lfVector *lB, lfVector *z
return conjgrad_loopcount<conjgrad_looplimit; // true means we reached desired accuracy in given time - ie stable
}
+#else
+static int cg_filtered(lfVector *ldV, fmatrix3x3 *lA, lfVector *lB, lfVector *z, fmatrix3x3 *S)
+{
+ // Solves for unknown X in equation AX=B
+ unsigned int conjgrad_loopcount=0, conjgrad_looplimit=100;
+ float conjgrad_epsilon=0.0001f /* , conjgrad_lasterror=0 */ /* UNUSED */;
+
+ unsigned int numverts = lA[0].vcount;
+ lfVector *fB = create_lfvector(numverts);
+ lfVector *AdV = create_lfvector(numverts);
+ lfVector *r = create_lfvector(numverts);
+ lfVector *c = create_lfvector(numverts);
+ lfVector *q = create_lfvector(numverts);
+ lfVector *s = create_lfvector(numverts);
+ float delta_new, delta_old, delta_target, alpha;
+
+ cp_lfvector(ldV, z, numverts);
+
+ /* d0 = filter(B)^T * P * filter(B) */
+ cp_lfvector(fB, lB, numverts);
+ filter(fB, S);
+ delta_target = conjgrad_epsilon*conjgrad_epsilon * dot_lfvector(fB, fB, numverts);
+
+ /* r = filter(B - A * dV) */
+ mul_bfmatrix_lfvector(AdV, lA, ldV);
+ sub_lfvector_lfvector(r, lB, AdV, numverts);
+ filter(r, S);
+
+ /* c = filter(P^-1 * r) */
+ cp_lfvector(c, r, numverts);
+ filter(c, S);
+
+ /* delta = r^T * c */
+ delta_new = dot_lfvector(r, c, numverts);
+
+ while (delta_new > delta_target && conjgrad_loopcount < conjgrad_looplimit) {
+ mul_bfmatrix_lfvector(q, lA, c);
+ filter(q, S);
+
+ alpha = delta_new / dot_lfvector(c, q, numverts);
+
+ add_lfvector_lfvectorS(ldV, ldV, c, alpha, numverts);
+
+ add_lfvector_lfvectorS(r, r, q, -alpha, numverts);
+
+ /* s = P^-1 * r */
+ cp_lfvector(s, r, numverts);
+ delta_old = delta_new;
+ delta_new = dot_lfvector(r, s, numverts);
+
+ add_lfvector_lfvectorS(c, s, c, delta_new / delta_old, numverts);
+ filter(c, S);
+
+ conjgrad_loopcount++;
+ }
+
+ del_lfvector(fB);
+ del_lfvector(AdV);
+ del_lfvector(r);
+ del_lfvector(c);
+ del_lfvector(q);
+ del_lfvector(s);
+ // printf("W/O conjgrad_loopcount: %d\n", conjgrad_loopcount);
+
+ return conjgrad_loopcount < conjgrad_looplimit; // true means we reached desired accuracy in given time - ie stable
+}
+#endif
// block diagonalizer
DO_INLINE void BuildPPinv(fmatrix3x3 *lA, fmatrix3x3 *P, fmatrix3x3 *Pinv)
@@ -1880,10 +1957,12 @@ static void setup_constraint_matrix(ClothVertex *verts, int numverts, ColliderCo
/* pinned vertex constraints */
for (i = 0; i < numverts; i++) {
S[i].c = S[i].r = i;
- if (verts[i].flags & CLOTH_VERT_FLAG_PINNED)
+ if (verts[i].flags & CLOTH_VERT_FLAG_PINNED) {
zero_m3(S[i].m);
- else
+ }
+ else {
unit_m3(S[i].m);
+ }
}
for (i = 0; i < totcolliders; ++i) {
@@ -1891,12 +1970,14 @@ static void setup_constraint_matrix(ClothVertex *verts, int numverts, ColliderCo
for (j = 0; j < ct->totcollisions; ++j) {
CollPair *collpair = &ct->collisions[j];
int v = collpair->face1;
+ float cmat[3][3];
/* pinned verts handled separately */
if (verts[v].flags & CLOTH_VERT_FLAG_PINNED)
continue;
- zero_m3(S[v].m);
+ mul_fvectorT_fvector(cmat, collpair->normal, collpair->normal);
+ sub_m3_m3m3(S[v].m, I, cmat);
}
}
}
@@ -2047,18 +2128,22 @@ static void cloth_calc_force(ClothModifierData *clmd, float UNUSED(frame), lfVec
cloth_apply_spring_force(clmd, search->link, lF, lX, lV, dFdV, dFdX);
search = search->next;
}
+// printf("====== dFdV ======\n");
+// print_sparse_matrix(dFdV);
+// printf("============\n");
// printf("\n");
}
-static void simulate_implicit_euler(Implicit_Data *id, float dt)
+static bool simulate_implicit_euler(Implicit_Data *id, float dt)
{
unsigned int numverts = id->dFdV[0].vcount;
+ bool ok;
lfVector *dFdXmV = create_lfvector(numverts);
zero_lfvector(id->dV, numverts);
-
+
cp_bfmatrix(id->A, id->M);
-
+
subadd_bfmatrixS_bfmatrixS(id->A, id->dFdV, dt, id->dFdX, (dt*dt));
mul_bfmatrix_lfvector(dFdXmV, id->dFdX, id->V);
@@ -2067,7 +2152,7 @@ static void simulate_implicit_euler(Implicit_Data *id, float dt)
// itstart();
- cg_filtered(id->dV, id->A, id->B, id->z, id->S); /* conjugate gradient algorithm to solve Ax=b */
+ ok = cg_filtered(id->dV, id->A, id->B, id->z, id->S); /* conjugate gradient algorithm to solve Ax=b */
// cg_filtered_pre(id->dV, id->A, id->B, id->z, id->S, id->P, id->Pinv, id->bigI);
// itend();
@@ -2077,6 +2162,8 @@ static void simulate_implicit_euler(Implicit_Data *id, float dt)
add_lfvector_lfvector(id->Vnew, id->V, id->dV, numverts);
del_lfvector(dFdXmV);
+
+ return ok;
}
/* computes where the cloth would be if it were subject to perfectly stiff edges
@@ -2226,6 +2313,13 @@ int implicit_solver(Object *ob, float frame, ClothModifierData *clmd, ListBase *
}
copy_v3_v3(verts[i].txold, id->X[i]);
+
+// if (!(verts[i].flags & CLOTH_VERT_FLAG_PINNED) && i > 0)
+// BKE_sim_debug_data_add_line(clmd->debug_data, id->Xnew[i], id->Xnew[i-1], 1, 0.5, 0.5, "hair", hash_vertex(4892, i));
+// BKE_sim_debug_data_add_vector(clmd->debug_data, id->Xnew[i], id->Vnew[i], 0, 0, 1, "velocity", hash_vertex(3158, i));
+ if (!(verts[i].flags & CLOTH_VERT_FLAG_PINNED) && i > 0)
+ BKE_sim_debug_data_add_line(clmd->debug_data, id->X[i], id->X[i-1], 1, 0.5, 0.5, "hair", hash_vertex(4892, i));
+ BKE_sim_debug_data_add_vector(clmd->debug_data, id->X[i], id->V[i], 0, 0, 1, "velocity", hash_vertex(3158, i));
}
#if 0
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