[Bf-blender-cvs] [cbd0d7a] alembic: Alternative implementation for goal spring targets as vertices.
Lukas Tönne
noreply at git.blender.org
Fri May 1 15:53:45 CEST 2015
Commit: cbd0d7a6b4c5f66850d301ea4668c5812939e1ed
Author: Lukas Tönne
Date: Fri May 1 15:51:14 2015 +0200
Branches: alembic
https://developer.blender.org/rBcbd0d7a6b4c5f66850d301ea4668c5812939e1ed
Alternative implementation for goal spring targets as vertices.
When using external forces to implement goal springs to explicit
positions in space, the system cannot calculate a stable solution based
on the goal velocities. The new approach implements goals as vertices
in the simulation, which are constrained to their animated locations.
This way they are treated like regular vertices, but the springs only
affect their non-constrained counterpart (the actual vertices).
===================================================================
M source/blender/physics/intern/BPH_mass_spring.cpp
===================================================================
diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 8a6e8e1..0c18e24 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -1130,6 +1130,7 @@ struct Implicit_Data *BPH_strands_solver_create(struct Strands *strands, struct
struct Implicit_Data *id;
int numverts = strands->totverts;
int numcurves = strands->totcurves;
+ int numgoalverts = numverts - numcurves; /* extra virtual vertices to act as goal spring targets */
int numedges = max_ii(numverts - numcurves, 0);
int numbends = max_ii(numverts - 2*numcurves, 0);
@@ -1137,20 +1138,25 @@ struct Implicit_Data *BPH_strands_solver_create(struct Strands *strands, struct
* stretch springs: 1 per edge
* bending sprints: 3 per bend // XXX outdated, 1 is enough
*/
- int numsprings = (numverts-numcurves) + numedges + 3*numbends;
+ int numsprings = numgoalverts + numedges + 3*numbends;
int i;
- id = BPH_mass_spring_solver_create(numverts, numsprings);
+ id = BPH_mass_spring_solver_create(numverts + numgoalverts, numsprings);
for (i = 0; i < numverts; i++) {
- // TODO define mass
float mass = params->mass;
BPH_mass_spring_set_vertex_mass(id, i, mass);
}
+ for (i = numverts; i < numverts + numgoalverts; i++) {
+ BPH_mass_spring_set_vertex_mass(id, i, 1.0f);
+ }
for (i = 0; i < numverts; i++) {
BPH_mass_spring_set_rest_transform(id, i, I3);
}
+ for (i = numverts; i < numverts + numgoalverts; i++) {
+ BPH_mass_spring_set_rest_transform(id, i, I3);
+ }
return id;
}
@@ -1177,6 +1183,15 @@ static void strands_setup_constraints(Strands *strands, Implicit_Data *data, Col
// }
}
+ /* pin virtual goal targets */
+ {
+ int goalstart = strands->totverts;
+ int goalend = goalstart + strands->totverts - strands->totcurves;
+ for (int i = goalstart; i < goalend; ++i) {
+ BPH_mass_spring_add_constraint_ndof0(data, i, ZERO); /* velocity is defined externally */
+ }
+ }
+
#if 0
for (i = 0; i < totcolliders; ++i) {
ColliderContacts *ct = &contacts[i];
@@ -1373,8 +1388,33 @@ static float strands_goal_stiffness(Strands *UNUSED(strands), HairSimParams *par
}
/* goal forces pull vertices toward their rest position */
-static void strands_calc_vertex_goal_forces(Strands *strands, float space[4][4], HairSimParams *params, Implicit_Data *data, StrandIterator *it_strand)
+static void strands_calc_vertex_goal_forces(Strands *strands, float UNUSED(space[4][4]), HairSimParams *params, Implicit_Data *data, StrandIterator *it_strand)
{
+ const int goalstart = strands->totverts;
+ StrandEdgeIterator it_edge;
+
+ float length = 0.0f;
+ for (BKE_strand_edge_iter_init(&it_edge, it_strand); BKE_strand_edge_iter_valid(&it_edge); BKE_strand_edge_iter_next(&it_edge))
+ length += len_v3v3(it_edge.vertex1->co, it_edge.vertex0->co);
+ float length_inv = length > 0.0f ? 1.0f / length : 0.0f;
+
+ float t = 0.0f;
+ for (BKE_strand_edge_iter_init(&it_edge, it_strand); BKE_strand_edge_iter_valid(&it_edge); BKE_strand_edge_iter_next(&it_edge)) {
+ int vj = BKE_strand_edge_iter_vertex1_offset(strands, &it_edge);
+ int numroots = it_strand->index + 1; /* roots don't have goal verts, skip this many */
+ int goalj = goalstart + vj - numroots;
+
+ float restlen = len_v3v3(it_edge.vertex1->co, it_edge.vertex0->co);
+ t += restlen;
+
+ float stiffness = strands_goal_stiffness(strands, params, it_edge.vertex1, t * length_inv);
+ float damping = stiffness * params->goal_damping;
+
+ float f[3];
+ BPH_mass_spring_force_spring_linear(data, vj, goalj, 0.0f, stiffness, damping, true, 0.0f, f, NULL, NULL);
+ }
+
+#if 0
StrandEdgeIterator it_edge;
float rootvel[3];
@@ -1399,6 +1439,7 @@ static void strands_calc_vertex_goal_forces(Strands *strands, float space[4][4],
float f[3];
BPH_mass_spring_force_spring_goal(data, vj, goal, rootvel, stiffness, damping, f, NULL, NULL);
}
+#endif
}
/* calculates internal forces for a single strand curve */
@@ -1508,6 +1549,61 @@ static void strands_calc_root_location(Strands *strands, float mat[4][4], Implic
}
}
+/* calculates the location of virtual goal vertices */
+static void strands_calc_goal_velocities(Strands *strands, float mat[4][4], Implicit_Data *data, float timestep)
+{
+ const int goalstart = strands->totverts;
+ int goalindex = goalstart;
+
+ StrandIterator it_strand;
+ for (BKE_strand_iter_init(&it_strand, strands); BKE_strand_iter_valid(&it_strand); BKE_strand_iter_next(&it_strand)) {
+ StrandVertexIterator it_vert;
+ for (BKE_strand_vertex_iter_init(&it_vert, &it_strand); BKE_strand_vertex_iter_valid(&it_vert); BKE_strand_vertex_iter_next(&it_vert)) {
+ /* skip root */
+ if (it_vert.index == 0)
+ continue;
+
+ int index = BKE_strand_vertex_iter_vertex_offset(strands, &it_vert);
+
+ float vel[3];
+ sub_v3_v3v3(vel, strands->verts[index].co, strands->state[index].co);
+ mul_v3_fl(vel, 1.0f/timestep);
+ mul_mat3_m4_v3(mat, vel);
+
+ BPH_mass_spring_set_velocity(data, goalindex, vel);
+
+ ++goalindex;
+ }
+ }
+}
+
+/* calculates the location of virtual goal vertices */
+static void strands_calc_goal_locations(Strands *strands, float mat[4][4], Implicit_Data *data, float step)
+{
+ const int goalstart = strands->totverts;
+ int goalindex = goalstart;
+
+ StrandIterator it_strand;
+ for (BKE_strand_iter_init(&it_strand, strands); BKE_strand_iter_valid(&it_strand); BKE_strand_iter_next(&it_strand)) {
+ StrandVertexIterator it_vert;
+ for (BKE_strand_vertex_iter_init(&it_vert, &it_strand); BKE_strand_vertex_iter_valid(&it_vert); BKE_strand_vertex_iter_next(&it_vert)) {
+ /* skip root */
+ if (it_vert.index == 0)
+ continue;
+
+ int index = BKE_strand_vertex_iter_vertex_offset(strands, &it_vert);
+
+ float co[3];
+ interp_v3_v3v3(co, strands->state[index].co, strands->verts[index].co, step);
+ mul_m4_v3(mat, co);
+
+ BPH_mass_spring_set_position(data, goalindex, co);
+
+ ++goalindex;
+ }
+ }
+}
+
/* XXX Do we need to take fictitious forces from the moving and/or accelerated frame of reference into account?
* This would mean we pass not only the basic world transform mat, but also linear/angular velocity and acceleration.
*/
@@ -1544,6 +1640,9 @@ bool BPH_strands_solve(Strands *strands, float mat[4][4], Implicit_Data *id, Hai
}
strands_calc_root_velocity(strands, mat, id, timestep);
+ strands_calc_goal_locations(strands, mat, id, 0.0f);
+ strands_calc_goal_velocities(strands, mat, id, timestep);
+
for (float step = 0.0f; step < 1.0f; step += dstep) {
ImplicitSolverResult result;
@@ -1579,6 +1678,7 @@ bool BPH_strands_solve(Strands *strands, float mat[4][4], Implicit_Data *id, Hai
/* move pinned verts to correct position */
strands_calc_root_location(strands, mat, id, step + dstep);
+ strands_calc_goal_locations(strands, mat, id, step + dstep);
#if 0
/* free contact points */
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