Move mesh inertia specification from global <compiler> to <asset/mesh>.

Three options:
- Convex: Use convex hull
- Exact: Use exact geometry (requires watertight mesh)
- Legacy: Legacy approximation (deprecated)

Fixes #2152

PiperOrigin-RevId: 688949900
Change-Id: I4537f343db917195c6fd58d517b189d5ee3be1cd

src/user/user_init.c

@@ -246,6 +246,7 @@ void mjs_defaultMesh(mjsMesh* mesh) {
   mesh->refquat[0] = 1;
   mesh->scale[0] = mesh->scale[1] = mesh->scale[2] = 1;
   mesh->maxhullvert = -1;
+  mesh->inertia = mjINERTIA_LEGACY;
 }
 
 

src/user/user_mesh.cc

@@ -1250,22 +1250,24 @@ void mjCMesh::LoadMSH(mjResource* resource) {
 
 
 void mjCMesh::ComputeVolume(double CoM[3], mjtGeomInertia type,
-                              const double facecen[3], bool exactmeshinertia) {
+                              const double facecen[3]) {
   double nrm[3];
   double cen[3];
   GetVolumeRef(type) = 0;
   mjuu_zerovec(CoM, 3);
-  for (int i=0; i < nface(); i++) {
+  int nf = (inertia == mjINERTIA_CONVEX) ? graph_[1] : nface();
+  int* f = (inertia == mjINERTIA_CONVEX) ? graph_ + 2 + 3*(graph_[0]+graph_[1]) : face_.data();
+  float* vv = vert_.data();
+  for (int i=0; i < nf; i++) {
     // get area, normal and center
-    float* vv = vert_.data();
-    double a = _triangle(nrm, cen, vv+3*face_[3*i], vv+3*face_[3*i+1], vv+3*face_[3*i+2]);
+    double a = _triangle(nrm, cen, vv+3*f[3*i], vv+3*f[3*i+1], vv+3*f[3*i+2]);
 
     // compute and add volume
     const double vec[3] = {cen[0]-facecen[0], cen[1]-facecen[1], cen[2]-facecen[2]};
     double vol = type==mjINERTIA_SHELL ? a : mjuu_dot3(vec, nrm) * a / 3;
 
     // if legacy computation requested, then always positive
-    if (!exactmeshinertia && type==mjINERTIA_VOLUME) {
+    if (inertia == mjINERTIA_LEGACY) {
       vol = abs(vol);
     }
 
@@ -1410,21 +1412,17 @@ void mjCMesh::Process() {
   for ( const auto type : { mjtGeomInertia::mjINERTIA_VOLUME, mjtGeomInertia::mjINERTIA_SHELL } ) {
     double CoM[3] = {0, 0, 0};
     double inert[6] = {0, 0, 0, 0, 0, 0};
-    bool exactmeshinertia = model->exactmeshinertia;
 
     // compute CoM and volume from pyramid volumes
-    ComputeVolume(CoM, type, facecen, model->exactmeshinertia);
+    ComputeVolume(CoM, type, facecen);
 
-    // perform computation with convex mesh if volume is negative
-    if (GetVolumeRef(type) <= 0 && exactmeshinertia) {
-      mju_warning("Malformed mesh '%s', computing mesh inertia from convex hull", name.c_str());
-      exactmeshinertia = false;
-      ComputeVolume(CoM, type, facecen, exactmeshinertia);
-    }
-
-    // if volume is still invalid, skip the rest of the computations
+    // if volume is invalid, skip the rest of the computations
     if (GetVolumeRef(type) < mjMINVAL) {
-      validvolume_ = GetVolumeRef(type) < 0 ? -1 : 0;
+      if (type == mjINERTIA_SHELL) {
+        validarea_ = 0;
+      } else {
+        validvolume_ = GetVolumeRef(type) < 0 ? -1 : 0;
+      }
       continue;
     }
 
@@ -1447,17 +1445,19 @@ void mjCMesh::Process() {
     const int k[6][2] = {{0, 0}, {1, 1}, {2, 2}, {0, 1}, {0, 2}, {1, 2}};
     double P[6] = {0, 0, 0, 0, 0, 0};
     GetVolumeRef(type) = 0;
-    for (int i=0; i < nface(); i++) {
-      float* D = vert_.data()+3*face_[3*i];
-      float* E = vert_.data()+3*face_[3*i+1];
-      float* F = vert_.data()+3*face_[3*i+2];
+    int nf = (inertia == mjINERTIA_CONVEX) ? graph_[1] : nface();
+    int* f = (inertia == mjINERTIA_CONVEX) ? graph_ + 2 + 3*(graph_[0]+graph_[1]) : face_.data();
+    for (int i=0; i < nf; i++) {
+      float* D = vert_.data()+3*f[3*i];
+      float* E = vert_.data()+3*f[3*i+1];
+      float* F = vert_.data()+3*f[3*i+2];
 
       // get area, normal and center; update volume
       double a = _triangle(nrm, cen, D, E, F);
       double vol = type==mjINERTIA_SHELL ? a : mjuu_dot3(cen, nrm) * a / 3;
 
       // if legacy computation requested, then always positive
-      if (!exactmeshinertia && type==mjINERTIA_VOLUME) {
+      if (inertia == mjINERTIA_LEGACY) {
         vol = abs(vol);
       }
 
@@ -1554,7 +1554,7 @@ void mjCMesh::CheckMesh(mjtGeomInertia type) {
   if (!processed_) {
     return;
   }
-  if ((invalidorientation_.first>=0 || invalidorientation_.second>=0) && model->exactmeshinertia)
+  if ((invalidorientation_.first>=0 || invalidorientation_.second>=0) && inertia == mjINERTIA_EXACT)
     throw mjCError(this,
                    "faces of mesh '%s' have inconsistent orientation. Please check the "
                    "faces containing the vertices %d and %d.",

src/user/user_objects.h

@@ -868,6 +868,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   const std::vector<float>& UserTexcoord() const { return spec_texcoord_; }
   const std::vector<int>& Face() const { return face_; }
   const std::vector<int>& UserFace() const { return spec_face_; }
+  mjtMeshInertia Inertia() const { return spec.inertia; }
 
   // setters
   void SetNeedHull(bool needhull) { needhull_ = needhull; }
@@ -945,8 +946,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   std::vector<unsigned char> num_face_vertices_;
 
   // compute the volume and center-of-mass of the mesh given the face center
-  void ComputeVolume(double CoM[3], mjtGeomInertia type, const double facecen[3],
-                     bool exactmeshinertia);
+  void ComputeVolume(double CoM[3], mjtGeomInertia gtype, const double facecen[3]);
 };