Remove copy_back from Python bindings and mj_copyBack from the C API.

PiperOrigin-RevId: 687377331
Change-Id: I355493d92857418b08b5aa90ea38cebe5c475314

src/user/user_api.cc

@@ -75,14 +75,6 @@ mjSpec* mj_copySpec(const mjSpec* s) {
 
 
 
-// copy back model
-void mj_copyBack(mjSpec* s, const mjModel* m) {
-  mjCModel* modelC = static_cast<mjCModel*>(s->element);
-  modelC->CopyBack(m);
-}
-
-
-
 // compile model
 mjModel* mj_compile(mjSpec* s, const mjVFS* vfs) {
   mjCModel* modelC = static_cast<mjCModel*>(s->element);

src/user/user_api.h

@@ -54,9 +54,6 @@ MJAPI const char* mjs_getError(mjSpec* s);
 // Return 1 if compiler error is a warning.
 MJAPI int mjs_isWarning(mjSpec* s);
 
-// Copy model fields back into spec.
-MJAPI void mj_copyBack(mjSpec* s, const mjModel* m);
-
 // Delete spec.
 MJAPI void mj_deleteSpec(mjSpec* s);
 

src/xml/xml.cc

@@ -395,7 +395,7 @@ mjSpec* ParseSpecFromString(std::string_view xml, char* error, int nerror) {
 }
 
 // Main writer function - calls mjXWrite
-std::string WriteXML(const mjSpec* spec, char* error, int nerror) {
+std::string WriteXML(const mjModel* m, const mjSpec* spec, char* error, int nerror) {
   LocaleOverride locale_override;
 
   // check for empty model
@@ -405,7 +405,7 @@ std::string WriteXML(const mjSpec* spec, char* error, int nerror) {
   }
 
   mjXWriter writer;
-  writer.SetModel(spec);
+  writer.SetModel(spec, m);
 
   try {
     return writer.Write(error, nerror);

src/xml/xml.h

@@ -29,6 +29,6 @@ mjSpec* ParseXML(const char* filename, const mjVFS* vfs, char* error, int nerror
 mjSpec* ParseSpecFromString(std::string_view xml, char* error = nullptr, int nerror = 0);
 
 // Main writer function
-std::string WriteXML(const mjSpec* spec, char* error, int nerror);
+std::string WriteXML(const mjModel* m, const mjSpec* spec, char* error, int nerror);
 
 #endif  // MUJOCO_SRC_XML_XML_H_

src/xml/xml_api.cc

@@ -62,8 +62,7 @@ std::optional<std::string> GlobalModel::ToXML(const mjModel* m, char* error,
     mjCopyError(error, "No XML model loaded", error_sz);
     return std::nullopt;
   }
-  mj_copyBack(spec_, m);
-  std::string result = WriteXML(spec_, error, error_sz);
+  std::string result = WriteXML(m, spec_, error, error_sz);
   if (result.empty()) {
     return std::nullopt;
   }
@@ -229,7 +228,7 @@ mjSpec* mj_parseXMLString(const char* xml, const mjVFS* vfs, char* error, int er
 
 // save spec to XML file, return 1 on success, 0 otherwise
 int mj_saveXML(const mjSpec* s, const char* filename, char* error, int error_sz) {
-  std::string result = WriteXML(s, error, error_sz);
+  std::string result = WriteXML(NULL, s, error, error_sz);
   if (result.empty()) {
     return 0;
   }
@@ -245,7 +244,7 @@ int mj_saveXML(const mjSpec* s, const char* filename, char* error, int error_sz)
 
 // save spec to string, return 1 on success, 0 otherwise
 int mj_saveXMLString(const mjSpec* s, char* xml, int xml_sz, char* error, int error_sz) {
-  std::string result = WriteXML(s, error, error_sz);
+  std::string result = WriteXML(NULL, s, error, error_sz);
   if (result.size() >= xml_sz) {
     std::string error_msg = "Output string too short, should be at least " +
                             std::to_string(result.size()+1);

src/xml/xml_base.cc

@@ -21,6 +21,7 @@
 #include <string>
 #include <vector>
 
+#include <mujoco/mjmodel.h>
 #include <mujoco/mjspec.h>
 #include "xml/xml_util.h"
 #include "tinyxml2.h"
@@ -43,7 +44,7 @@ mjXBase::mjXBase() {
 
 
 // set model field
-void mjXBase::SetModel(const mjSpec* _model) {
+void mjXBase::SetModel(const mjSpec* _model, const mjModel* m) {
   spec = (mjSpec*)_model;
 }
 

src/xml/xml_base.h

@@ -88,7 +88,7 @@ class mjXBase : public mjXUtil {
   };
 
   // set the model allocated externally
-  virtual void SetModel(const mjSpec*);
+  virtual void SetModel(const mjSpec*, const mjModel* = nullptr);
 
   // read alternative orientation specification
   static int ReadAlternative(tinyxml2::XMLElement* elem, mjsOrientation& alt);

src/xml/xml_native_writer.cc

@@ -853,9 +853,12 @@ mjXWriter::mjXWriter(void) {
 
 
 // cast model
-void mjXWriter::SetModel(const mjSpec* spec) {
-  if (spec) {
-    model = (mjCModel*)spec->element;
+void mjXWriter::SetModel(const mjSpec* _spec, const mjModel* m) {
+  if (_spec) {
+    model = (mjCModel*)_spec->element;
+  }
+  if (m) {
+    model->CopyBack(m);
   }
 }
 

src/xml/xml_native_writer.h

@@ -19,6 +19,7 @@
 #include <string>
 #include <string_view>
 
+#include <mujoco/mjmodel.h>
 #include <mujoco/mjspec.h>
 #include "user/user_objects.h"
 #include "xml/xml_base.h"
@@ -28,7 +29,7 @@ class mjXWriter : public mjXBase {
  public:
   mjXWriter();                                        // constructor
   virtual ~mjXWriter() = default;                     // destructor
-  void SetModel(const mjSpec* spec);
+  void SetModel(const mjSpec* _spec, const mjModel* m = nullptr);
 
   // write XML document to string
   std::string Write(char *error, std::size_t error_sz);