Change mj_encode return type to 64-bit (mjtSize)

This supports encoding files larger than 2GB.

PiperOrigin-RevId: 939828697
Change-Id: If60d36c61475ced20b4eb58408ffb37e25bf3db7

doc/APIreference/APItypes.rst

@@ -2053,8 +2053,8 @@ mjfEncode
 
 .. code-block:: C
 
-   typedef int (*mjfEncode)(const mjSpec* s, const mjModel* m, const mjVFS* vfs,
-                            mjResource* resource);
+   typedef mjtSize (*mjfEncode)(const mjSpec* s, const mjModel* m, const mjVFS* vfs,
+                                mjResource* resource);
 
 
 This callback populates the :ref:`mjResource<mjResource>` `data` member with bytes representing the

doc/changelog.rst

@@ -10,6 +10,11 @@ General
 - Added Nesterov momentum extrapolation with adaptive gradient restart (O'Donoghue-Candès) to the PGS solver,
   significantly improving convergence. Overall PGS now requires ~2x fewer iterations.
 
+.. admonition:: Breaking API changes
+   :class: attention
+
+   - Return type of :ref:`mj_encode` and the :ref:`mjfEncode` callback changed from ``int`` to ``mjtSize`` (64-bit).
+
 Version 3.10.0 (June 22, 2026)
 ------------------------------
 

doc/includes/references.h

@@ -3231,9 +3231,9 @@ mjSpec* mj_parseXML(const char* filename, const mjVFS* vfs, char* error, int err
 mjSpec* mj_parseXMLString(const char* xml, const mjVFS* vfs, char* error, int error_sz);
 mjSpec* mj_parse(const char* filename, const char* content_type,
                  const mjVFS* vfs, char* error, int error_sz);
-int mj_encode(const mjSpec* s, const mjModel* m, const char* filename,
-              const char* content_type, const mjVFS* vfs, char* error,
-              int error_sz);
+mjtSize mj_encode(const mjSpec* s, const mjModel* m, const char* filename,
+                  const char* content_type, const mjVFS* vfs, char* error,
+                  int error_sz);
 mjModel* mj_compile(mjSpec* s, const mjVFS* vfs);
 int mj_copyBack(mjSpec* s, const mjModel* m);
 int mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d);