Add defaults to SDF plugin attributes.

Expose diameter and number of teeth for the gear SDF.

PiperOrigin-RevId: 577779297
Change-Id: Iec5890ab7f39080b395cf06a76f9c2216f4f39ed

include/mujoco/mjplugin.h

@@ -17,6 +17,7 @@
 
 #include <mujoco/mjdata.h>
 #include <mujoco/mjmodel.h>
+#include <mujoco/mjtnum.h>
 #include <mujoco/mjvisualize.h>
 
 
@@ -117,6 +118,9 @@ struct mjpPlugin_ {
   // called during compilation for marching cubes
   mjtNum (*sdf_staticdistance)(const mjtNum point[3], const mjtNum* attributes);
 
+  // convert attributes and provide defaults if not present
+  void (*sdf_attribute)(mjtNum attribute[], const char* name[], const char* value[]);
+
   // bounding box of implicit surface
   void (*sdf_aabb)(mjtNum aabb[6], const mjtNum* attributes);
 };