[Python Viewer] Allow users to override rendering flags via user_scn.

Fixes #1190

PiperOrigin-RevId: 603672602
Change-Id: I3ff1bb0dca7e913b36f1b241aaea8b8bb95cadff

simulate/simulate.cc

@@ -2091,6 +2091,17 @@ void Simulate::Sync() {
       }
     }
 
+    // pick up rendering flags changed via user_scn
+    if (user_scn) {
+      for (int i = 0; i < mjNRNDFLAG; ++i) {
+        if (user_scn->flags[i] != user_scn_flags_prev_[i]) {
+          scn.flags[i] = user_scn->flags[i];
+        }
+      }
+      Copy(user_scn->flags, scn.flags);
+      Copy(user_scn_flags_prev_, user_scn->flags);
+    }
+
     mjopt_prev_ = scnstate_.model.opt;
     warn_vgeomfull_prev_ = scnstate_.data.warning[mjWARN_VGEOMFULL].number;
   }
@@ -2270,6 +2281,11 @@ void Simulate::LoadOnRenderThread() {
     this->scn.flags[mjRND_REFLECTION] = 0;
   }
 
+  if (this->user_scn) {
+    Copy(this->user_scn->flags, this->scn.flags);
+    Copy(this->user_scn_flags_prev_, this->scn.flags);
+  }
+
   // clear perturbation state
   this->pert.active = 0;
   this->pert.select = 0;

simulate/simulate.h

@@ -130,6 +130,7 @@ class Simulate {
   mjOption mjopt_prev_;
   mjvOption opt_prev_;
   mjvCamera cam_prev_;
+
   int warn_vgeomfull_prev_;
 
   // pending GUI-driven actions, to be applied at the next call to Sync
@@ -247,6 +248,7 @@ class Simulate {
 
   // additional user-defined visualization geoms (used in passive mode)
   mjvScene* user_scn = nullptr;
+  mjtByte user_scn_flags_prev_[mjNRNDFLAG];
 
   // OpenGL rendering and UI
   int refresh_rate = 60;