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Implement multi-cell finite element method for interpolated flexes.

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This change introduces a `flex_cellcount` field to `mjModel` to specify the number of cells in each dimension for interpolated flexes. The stiffness computation, passive force calculation, and Jacobian derivatives are updated to operate on a per-cell basis, significantly improving performance by localizing computations to the nodes within each cell.

PiperOrigin-RevId: 901216393
Change-Id: Ic23132e609de11e71bb7fef8d1f139daad2ec264
This commit is contained in:
Alessio Quaglino
2026-04-17 04:10:54 -07:00
committed by Copybara-Service
parent 8415dff307
commit 6c7ed66781
36 changed files with 1777 additions and 1039 deletions
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src/xml/xml_native_reader.cc
+14 -3
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@@ -315,7 +315,7 @@ std::vector<const char*> MJCF[nMJCF] = {
{">"},
{">"},
{"flexcomp", "*", "name", "type", "group", "dim", "dof",
"count", "spacing", "radius", "rigid", "mass", "inertiabox",
"count", "cellcount", "spacing", "radius", "rigid", "mass", "inertiabox",
"scale", "file", "point", "element", "texcoord", "material", "rgba",
"flatskin", "pos", "quat", "axisangle", "xyaxes", "zaxis", "euler", "origin"},
{"<"},
@@ -334,8 +334,8 @@ std::vector<const char*> MJCF[nMJCF] = {
{"deformable", "*"},
{"<"},
{"flex", "*", "name", "group", "dim", "radius", "material",
"rgba", "flatskin", "body", "vertex", "element", "texcoord", "elemtexcoord", "node"},
{"flex", "*", "name", "group", "dim", "radius", "material", "rgba", "flatskin", "body",
"vertex", "element", "texcoord", "elemtexcoord", "node", "cellcount", "dof"},
{"<"},
{"contact", "?", "contype", "conaffinity", "condim", "priority",
"friction", "solmix", "solref", "solimp", "margin", "gap",
@@ -1501,6 +1501,16 @@ void mjXReader::OneFlex(XMLElement* elem, mjsFlex* flex) {
ReadAttrInt(elem, "dim", &flex->dim);
ReadAttrInt(elem, "group", &flex->group);
flex->cellcount[0] = 1;
flex->cellcount[1] = 1;
flex->cellcount[2] = 1;
ReadAttr(elem, "cellcount", 3, flex->cellcount, text);
flex->order = 0;
if (MapValue(elem, "dof", &n, fdof_map, mjNFCOMPDOFS)) {
flex->order = (n == mjFCOMPDOF_QUADRATIC) ? 2 : (n == mjFCOMPDOF_TRILINEAR ? 1 : 0);
}
// read data vectors
if (ReadAttrTxt(elem, "body", text, true)) {
mjs_setStringVec(flex->vertbody, text.c_str());
@@ -2794,6 +2804,7 @@ void mjXReader::OneFlexcomp(XMLElement* elem, mjsBody* body, const mjVFS* vfs) {
fcomp.type = (mjtFcompType)n;
}
ReadAttr(elem, "count", 3, fcomp.count, text);
ReadAttr(elem, "cellcount", 3, fcomp.cellcount, text);
ReadAttr(elem, "spacing", 3, fcomp.spacing, text);
ReadAttr(elem, "scale", 3, fcomp.scale, text);
ReadAttr(elem, "mass", 1, &fcomp.mass, text);