Add dof="2d" option to flexcomp for in-plane deformations.

PiperOrigin-RevId: 902620719
Change-Id: Ib06d3f7b9439e1d90a8373a4289ade0c327e72e4

src/user/user_flexcomp.cc

@@ -613,6 +613,17 @@ bool mjCFlexcomp::Make(mjsBody* body, char* error, int error_sz, const mjVFS* vf
         }
       }
 
+      // add two orthogonal sliders (x and y only)
+      else if (doftype == mjFCOMPDOF_2D) {
+        for (int j=0; j < 2; j++) {
+          mjsJoint* jnt = mjs_addJoint(pb, 0);
+          jnt->type = mjJNT_SLIDE;
+          mjuu_setvec(jnt->pos, 0, 0, 0);
+          mjuu_setvec(jnt->axis, 0, 0, 0);
+          jnt->axis[j] = 1;
+        }
+      }
+
       // construct body name, add to vertbody
       char txt[100];
       mju::sprintf_arr(txt, "%s_%d", name.c_str(), i);

src/user/user_flexcomp.h

@@ -45,6 +45,7 @@ typedef enum _mjtDof {
   mjFCOMPDOF_RADIAL,
   mjFCOMPDOF_TRILINEAR,
   mjFCOMPDOF_QUADRATIC,
+  mjFCOMPDOF_2D,
 
   mjNFCOMPDOFS
 } mjtDof;

src/xml/xml_native_reader.cc

@@ -932,7 +932,8 @@ const mjMap fdof_map[mjNFCOMPDOFS] = {
   {"full",          mjFCOMPDOF_FULL},
   {"radial",        mjFCOMPDOF_RADIAL},
   {"trilinear",     mjFCOMPDOF_TRILINEAR},
-  {"quadratic",     mjFCOMPDOF_QUADRATIC}
+  {"quadratic",     mjFCOMPDOF_QUADRATIC},
+  {"2d",            mjFCOMPDOF_2D}
 };