Do not update qacc_warmstart at the end of the solver call; instead, update it at the same time as all other state variables. This change makes mj_forward idempotent.

See changelog herein for motivation and discussion.

PiperOrigin-RevId: 797392841
Change-Id: If50e9f09e1d07e8363169d3589c32097aeca2432

simulate/main.cc

@@ -285,7 +285,7 @@ mjModel* LoadModel(const char* file, mj::Simulate& sim) {
 
 // simulate in background thread (while rendering in main thread)
 void PhysicsLoop(mj::Simulate& sim) {
-  // cpu-sim syncronization point
+  // cpu-sim synchronization point
   std::chrono::time_point<mj::Simulate::Clock> syncCPU;
   mjtNum syncSim = 0;
 
@@ -438,6 +438,9 @@ void PhysicsLoop(mj::Simulate& sim) {
         else {
           // run mj_forward, to update rendering and joint sliders
           mj_forward(m, d);
+          if (sim.pause_update) {
+            mju_copy(d->qacc_warmstart, d->qacc, m->nv);
+          }
           sim.speed_changed = true;
         }
       }

simulate/simulate.cc

@@ -1922,8 +1922,8 @@ void Simulate::Sync(bool state_only) {
     return;
   }
 
-  bool update_profiler = this->profiler && (this->pause_update || this->run);
-  bool update_sensor = this->sensor && (this->pause_update || this->run);
+  bool update_profiler = this->profiler;
+  bool update_sensor = this->sensor;
 
   for (int i = 0; i < m_->njnt; ++i) {
     std::optional<std::pair<mjtNum, mjtNum>> range;

simulate/simulate.h

@@ -193,7 +193,7 @@ class Simulate {
   int info = 0;
   int profiler = 0;
   int sensor = 0;
-  int pause_update = 1;
+  int pause_update = 0;
   int fullscreen = 0;
   int vsync = 1;
   int busywait = 0;