Add control plugin API.

PiperOrigin-RevId: 493311715
Change-Id: Iccd99fb26004f39832818e378f01f9149a0e3e3b

doc/includes/references.h

@@ -1148,18 +1148,19 @@ struct mjModel_ {
   char*     names;                // names of all objects, 0-terminated       (nnames x 1)
 };
 typedef struct mjModel_ mjModel;
-typedef enum mjtPluginTypeBit_ {
+typedef enum mjtPluginCapabilityBit_ {
   mjPLUGIN_ACTUATOR = 1<<0,
   mjPLUGIN_SENSOR   = 1<<1,
   mjPLUGIN_PASSIVE  = 1<<2,
-} mjtPluginTypeBit;
+  mjPLUGIN_CONTROL  = 1<<3,
+} mjtPluginCapabilityBit;
 struct mjpPlugin_ {
   const char* name;    // globally unique name identifying the plugin
 
   int nattribute;                 // number of configuration attributes
   const char* const* attributes;  // name of configuration attributes
 
-  int type;            // bitfield of mjtPluginTypeBits specifying the plugin type
+  int capabilities;    // bitfield of mjtPluginCapabilityBit specifying optional plugin capabilities
   int needstage;       // an mjtStage enum value specifying the sensor computation stage
 
   // number of mjtNums needed to store the state of a plugin instance (required)
@@ -1181,10 +1182,13 @@ struct mjpPlugin_ {
   void (*reset)(const mjModel* m, mjData* d, int instance);
 
   // called when the plugin needs to update its outputs (required)
-  void (*compute)(const mjModel* m, mjData* d, int instance, int type);
+  void (*compute)(const mjModel* m, mjData* d, int instance, int capability_bit);
 
   // called when time integration occurs (optional)
   void (*advance)(const mjModel* m, mjData* d, int instance);
+
+  // called by mjv_updateScene (optional)
+  void (*visualize)(const mjModel*m, mjData* d, mjvScene* scn, int instance);
 };
 typedef struct mjpPlugin_ mjpPlugin;
 typedef enum mjtGridPos_ {        // grid position for overlay