Explicitly specify actdim on PID plugin actuators, to allow them to be used with keyframes.

Support actdim attribute on plugin actuators.

Remove the actuator_actdim callback. This callback leads to crashes when loading keyframes for models that have a stateful plugin.

PiperOrigin-RevId: 650649505
Change-Id: I40d1994d02ae4e20ce631b2702a984766cf2628e

plugin/actuator/pid.cc

@@ -117,6 +117,23 @@ std::unique_ptr<Pid> Pid::Create(const mjModel* m, int instance) {
     mju_warning("actuator not found for plugin instance %d", instance);
     return nullptr;
   }
+  // Validate actnum values for all actuators:
+  for (int actuator_id : actuators) {
+    int actnum = m->actuator_actnum[actuator_id];
+    int expected_actnum = Pid::ActDim(m, instance, actuator_id);
+    int dyntype = m->actuator_dyntype[actuator_id];
+    if (dyntype == mjDYN_FILTER || dyntype == mjDYN_FILTEREXACT ||
+        dyntype == mjDYN_INTEGRATOR) {
+      expected_actnum++;
+    }
+    if (actnum != expected_actnum) {
+      mju_warning(
+          "actuator %d has actdim %d, expected %d. Add actdim=\"%d\" to the "
+          "actuator plugin element.",
+          actuator_id, actnum, expected_actnum, expected_actnum);
+      return nullptr;
+    }
+  }
   return std::unique_ptr<Pid>(new Pid(config, std::move(actuators)));
 }
 
@@ -240,8 +257,6 @@ void Pid::RegisterPlugin() {
                                          kAttrIMax, kAttrSlewMax};
   plugin.nattribute = attributes.size();
   plugin.attributes = attributes.data();
-
-  plugin.actuator_actdim = Pid::ActDim;
   plugin.nstate = Pid::StateSize;
 
   plugin.init = +[](const mjModel* m, mjData* d, int instance) {

plugin/actuator/pid.h

@@ -52,9 +52,6 @@ class Pid {
   // Returns the number of state variables for the plugin instance
   static int StateSize(const mjModel* m, int instance);
 
-  // Returns the number of activation variables for the plugin instance
-  static int ActDim(const mjModel* m, int instance, int actuator_id);
-
   // Resets the C++ Pid instance's state.
   // plugin_state is a C array pointer into mjData->plugin_state, with a size
   // equal to the value returned from StateSize.
@@ -76,6 +73,9 @@ class Pid {
  private:
   Pid(PidConfig config, std::vector<int> actuators);
 
+  // Returns the expected number of activation variables for the instance.
+  static int ActDim(const mjModel* m, int instance, int actuator_id);
+
   struct State {
     mjtNum previous_ctrl = 0;
     // if using slew rate limits, mjData.act will contain an activation variable