Implement plugin mechanism for actuators and sensors.

PiperOrigin-RevId: 474874088
Change-Id: I65a8ffdf845f4fa0f8266c165883a747ab5812d8

include/mujoco/mjplugin.h

@@ -0,0 +1,61 @@
+// Copyright 2022 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MUJOCO_INCLUDE_MJPLUGIN_H_
+#define MUJOCO_INCLUDE_MJPLUGIN_H_
+
+#include <mujoco/mjdata.h>
+#include <mujoco/mjmodel.h>
+
+typedef enum mjtPluginTypeBit_ {
+  mjPLUGIN_ACTUATOR = 1<<0,
+  mjPLUGIN_SENSOR   = 1<<1
+} mjtPluginTypeBit;
+
+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 needstage;       // an mjtStage enum value specifying the sensor computation stage
+
+  // number of mjtNums needed to store the state of a plugin instance (required)
+  int (*nstate)(const mjModel* m, int instance);
+
+  // dimension of the specified sensor's output (required only for sensor plugins)
+  int (*nsensordata)(const mjModel* m, int instance, int sensor_id);
+
+  // called when a new mjData is being created (required)
+  void (*init)(const mjModel* m, mjData* d, int instance);
+
+  // called when an mjData is being freed (optional)
+  void (*destroy)(mjData* d, int instance);
+
+  // called when an mjData is being copied (optional)
+  void (*copy)(mjData* dest, const mjModel* m, const mjData* src, int instance);
+
+  // called when an mjData is being reset (required)
+  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);
+
+  // called when time integration occurs (optional)
+  void (*advance)(const mjModel* m, mjData* d, int instance);
+};
+typedef struct mjpPlugin_ mjpPlugin;
+
+#endif  // MUJOCO_INCLUDE_MJPLUGIN_H_