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Introduce trilinear flex parametrization.

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These flexes use only 24 DOFs (3 per vertex of the bounding box), while colliding with the full high resolution mesh.

On an 8x8x8 cube, the performance using DOFs at all vertices is

```
 Simulation time      : 18.74 s
 Steps per second     : 533
 Realtime factor      : 0.53 x
 Time per step        : 1874.4 µs

 Contacts per step    : 114.88
 Constraints per step : 3322.51
 Degrees of freedom   : 1536
```

With the new implementation, it is the following:

```
 Simulation time      : 1.82 s
 Steps per second     : 5507
 Realtime factor      : 5.51 x
 Time per step        : 181.6 µs

 Contacts per step    : 38.84
 Constraints per step : 155.36
 Degrees of freedom   : 24
```

PiperOrigin-RevId: 721008829
Change-Id: I833df027527db578d86667cc4b24295bcf6f7d22
This commit is contained in:
Alessio Quaglino
2025-01-29 09:37:37 -08:00
committed by Copybara-Service
parent 1a4b821b6b
commit 7cdf180641
47 changed files with 8967 additions and 96 deletions
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src/engine/engine_core_smooth.c
+40 -8
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@@ -453,19 +453,51 @@ void mj_flex(const mjModel* m, mjData* d) {
for (int f=0; f < m->nflex; f++) {
int vstart = m->flex_vertadr[f];
int vend = m->flex_vertadr[f] + m->flex_vertnum[f];
int nstart = m->flex_nodeadr[f];
int nend = m->flex_nodeadr[f] + m->flex_nodenum[f];
// centered: copy body position
if (m->flex_centered[f]) {
for (int i=vstart; i < vend; i++) {
mju_copy3(d->flexvert_xpos+3*i, d->xpos+3*m->flex_vertbodyid[i]);
// 0: vertices are the mesh vertices, 1: vertices are interpolated from nodal dofs
if (m->flex_interp[f] == 0) {
// centered: copy body position
if (m->flex_centered[f]) {
for (int i=vstart; i < vend; i++) {
mju_copy3(d->flexvert_xpos+3*i, d->xpos+3*m->flex_vertbodyid[i]);
}
}
// non-centered: map from local to global
else {
for (int i=vstart; i < vend; i++) {
mju_mulMatVec3(d->flexvert_xpos+3*i, d->xmat+9*m->flex_vertbodyid[i], m->flex_vert+3*i);
mju_addTo3(d->flexvert_xpos+3*i, d->xpos+3*m->flex_vertbodyid[i]);
}
}
}
// non-centered: map from local to global
// trilinear interpolation
else {
mjtNum nodexpos[mjMAXFLEXNODES];
if (m->flex_centered[f]) {
for (int i=nstart; i < nend; i++) {
mju_copy3(nodexpos + 3*(i-nstart), d->xpos + 3*m->flex_nodebodyid[i]);
}
} else {
for (int i=nstart; i < nend; i++) {
int j = i - nstart;
mju_mulMatVec3(nodexpos + 3*j, d->xmat + 9*m->flex_nodebodyid[i], m->flex_node + 3*i);
mju_addTo3(nodexpos + 3*j, d->xpos + 3*m->flex_nodebodyid[i]);
}
}
for (int i=vstart; i < vend; i++) {
mju_mulMatVec3(d->flexvert_xpos+3*i, d->xmat+9*m->flex_vertbodyid[i], m->flex_vert+3*i);
mju_addTo3(d->flexvert_xpos+3*i, d->xpos+3*m->flex_vertbodyid[i]);
mju_zero3(d->flexvert_xpos+3*i);
mjtNum* coord = m->flex_vert0 + 3*i;
for (int j=0; j < nend-nstart; j++) {
mjtNum coef = (j&1 ? coord[2] : 1-coord[2]) *
(j&2 ? coord[1] : 1-coord[1]) *
(j&4 ? coord[0] : 1-coord[0]);
mju_addToScl3(d->flexvert_xpos+3*i, nodexpos+3*j, coef);
}
}
}
}
@@ -542,7 +574,7 @@ void mj_flex(const mjModel* m, mjData* d) {
// compute lengths and Jacobians of edges
for (int f=0; f < m->nflex; f++) {
// skip if edges cannot generate forces
if (m->flex_rigid[f]) {
if (m->flex_rigid[f] || m->flex_interp[f]) {
continue;
}