Fix Filament crash when hiding geom groups

src/experimental/studio/hal/renderer_test.cc

@@ -68,6 +68,34 @@ TEST_F(RendererTest, OpengGlSoftware) {
   }
 }
 
+TEST_F(RendererTest, ToggleGeomGroupVisibility) {
+  mjSpec* spec = mj_makeSpec();
+  mjsGeom* geom = mjs_addGeom(mjs_findBody(spec, "world"), nullptr);
+  geom->type = mjGEOM_BOX;
+  geom->size[0] = 0.1;
+  geom->size[1] = 0.1;
+  geom->size[2] = 0.1;
+  geom->group = 2;
+  holder_ = ModelHolder::FromSpec(spec);
+  holder_->model()->vis.global.offwidth = width_;
+  holder_->model()->vis.global.offheight = height_;
+
+  FilamentRenderer renderer(nullptr, GraphicsMode::FilamentOpenGlSoftware);
+  renderer.Init(holder_->model());
+
+  mjvOption options;
+  mjv_defaultOption(&options);
+  std::vector<std::byte> pixels(width_ * height_ * 3);
+  renderer.Render(holder_->model(), holder_->data(), nullptr, nullptr, &options,
+                  width_, height_, pixels);
+  options.geomgroup[2] = 0;
+  renderer.Render(holder_->model(), holder_->data(), nullptr, nullptr, &options,
+                  width_, height_, pixels);
+  options.geomgroup[2] = 1;
+  renderer.Render(holder_->model(), holder_->data(), nullptr, nullptr, &options,
+                  width_, height_, pixels);
+}
+
 TEST_F(RendererTest, OpengGlHeadless) {
   FilamentRenderer renderer(nullptr, GraphicsMode::FilamentOpenGlHeadless);
   renderer.Init(holder_->model());

src/render/filament/core/renderable.cc

@@ -220,6 +220,7 @@ void Renderable::RemoveFromScene(filament::Scene* scene) {
   if (assigned_scene_ != scene) {
     mju_error("Attempting to remove renderable from wrong scene.");
   }
+  SetMaterialInstance(0);
   for (Part& part : parts_) {
     scene->remove(part.entity);
   }

src/render/filament/core/renderable.h

@@ -135,7 +135,7 @@ class Renderable : public mjrfRenderable {
   // of which instance, as well as other render state, to use with each render
   // request.
   struct DrawState {
-    MaterialManager::MaterialKey material_key;
+    MaterialManager::MaterialKey material_key = 0;
     bool cast_shadows = true;
     bool receive_shadows = true;
     bool wireframe = false;