Simplify mjs_addDefault.

PiperOrigin-RevId: 646534046
Change-Id: I658224e4800849231e68ed02d8fad07b8d796231

src/user/user_api.cc

@@ -437,10 +437,11 @@ mjsPlugin* mjs_addPlugin(mjSpec* s) {
 
 
 // add default to model
-mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, int parentid, int* id) {
+mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, const mjsDefault* parent) {
   mjCModel* modelC = static_cast<mjCModel*>(s->element);
-  *id = (int)modelC->NumDefaults();
-  mjCDef* def = modelC->AddDefault(classname, parentid);
+  mjCDef* parentC = parent ? static_cast<mjCDef*>(parent->element) :
+                             static_cast<mjCModel*>(s->element)->Defaults(0);
+  mjCDef* def = modelC->AddDefault(classname, parentC);
   if (def) {
     return &def->spec;
   } else {

src/user/user_api.h

@@ -156,7 +156,7 @@ MJAPI mjsKey* mjs_addKey(mjSpec* s);
 MJAPI mjsPlugin* mjs_addPlugin(mjSpec* s);
 
 // Add default.
-MJAPI mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, int parentid, int* id);
+MJAPI mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, const mjsDefault* parent);
 
 
 //---------------------------------- Add assets ----------------------------------------------------

src/user/user_model.cc

@@ -741,7 +741,9 @@ mjCDef* mjCModel::FindDefault(string name) {
 
 
 // add default class to array
-mjCDef* mjCModel::AddDefault(string name, int parentid) {
+mjCDef* mjCModel::AddDefault(string name, mjCDef* parent) {
+  int parentid = parent ? parent->id : 0;
+
   // check for repeated name
   int thisid = (int)defaults_.size();
   for (int i=0; i<thisid; i++) {
@@ -753,6 +755,7 @@ mjCDef* mjCModel::AddDefault(string name, int parentid) {
   // create new object
   mjCDef* def = new mjCDef;
   defaults_.push_back(def);
+  def->id = thisid;
 
   // initialize contents
   if (parentid>=0 && parentid<thisid) {

src/user/user_model.h

@@ -205,15 +205,15 @@ class mjCModel : public mjCModel_, private mjSpec {
   mjCBase* GetObject(mjtObj type, int id);  // pointer to specified object
 
   // API for access to other variables
-  bool IsCompiled() const;                                       // is model already compiled
-  const mjCError& GetError() const;                              // get reference of error object
-  mjCBody* GetWorld();                                           // pointer to world body
-  mjCDef* FindDefault(std::string name);                         // find defaults class name
-  mjCDef* AddDefault(std::string name, int parentid);            // add defaults class to array
-  mjCBase* FindObject(mjtObj type, std::string name) const;      // find object given type and name
-  mjCBody* FindBody(mjCBody* body, std::string name);            // find body given name
-  mjCFrame* FindFrame(mjCBody* body, std::string name) const;    // find frame given name
-  bool IsNullPose(const mjtNum* pos, const mjtNum* quat) const;  // detect null pose
+  bool IsCompiled() const;                                         // is model already compiled
+  const mjCError& GetError() const;                                // get reference of error object
+  mjCBody* GetWorld();                                             // pointer to world body
+  mjCDef* FindDefault(std::string name);                           // find defaults class name
+  mjCDef* AddDefault(std::string name, mjCDef* parent = nullptr);  // add defaults class to array
+  mjCBase* FindObject(mjtObj type, std::string name) const;        // find object given type and name
+  mjCBody* FindBody(mjCBody* body, std::string name);              // find body given name
+  mjCFrame* FindFrame(mjCBody* body, std::string name) const;      // find frame given name
+  bool IsNullPose(const mjtNum* pos, const mjtNum* quat) const;    // detect null pose
   void SetActivePlugins(const std::vector<std::pair<const mjpPlugin*, int>>&& active_plugins) {
     active_plugins_ = std::move(active_plugins);
   }

src/user/user_objects.cc

@@ -517,6 +517,7 @@ int mjCBoundingVolumeHierarchy::MakeBVH(
 // constructor
 mjCDef::mjCDef() {
   name.clear();
+  id = 0;
   parentid = -1;
   childid.clear();
   mjs_defaultJoint(&joint_.spec);

src/user/user_objects.h

@@ -1651,6 +1651,7 @@ class mjCDef : public mjsElement {
 
   // identifiers
   std::string name;               // class name
+  int id;                         // id of this default
   int parentid;                   // id of parent class
   std::vector<int> childid;       // ids of child classes