Clear material instance assignments at start of frame.

PiperOrigin-RevId: 945623848
Change-Id: I983efa6a14d25e2cb0f46b8bd529086d84247a50

src/render/filament/core/material_manager.cc

@@ -236,7 +236,11 @@ MaterialManager::MaterialKey MaterialManager::PrepareMaterialInstance(
   return key;
 }
 
-filament::MaterialInstance* MaterialManager::GetInstance(MaterialKey key) {
+const filament::MaterialInstance* MaterialManager::GetInstance(MaterialKey key) {
+  if (key == 0) {
+    return GetEngine()->getDefaultMaterial()->getDefaultInstance();
+  }
+
   auto it = instances_.find(key);
   if (it == instances_.end()) {
     return nullptr;

src/render/filament/core/material_manager.h

@@ -67,7 +67,7 @@ class MaterialManager {
                                       const Mesh* mesh);
 
   // Returns the MaterialInstance associated with the given key.
-  filament::MaterialInstance* GetInstance(MaterialKey key);
+  const filament::MaterialInstance* GetInstance(MaterialKey key);
 
   ObjectManager* GetObjectManager() const;
   filament::Engine* GetEngine() const;

src/render/filament/core/renderable.cc

@@ -239,6 +239,9 @@ const mjrfMaterial& Renderable::GetMaterial() const { return material_; }
 
 void Renderable::Prepare(std::span<const mjrfRenderRequest*> requests,
                          ReflectionManager* reflection_mgr) {
+  // Ensure the renderable has no material instances set from the previous
+  // frame. This will allow us to recycle material instances if needed.
+  SetMaterialInstance(0);
   // We assume BindMaterialInstance will be called with the same requests in
   // the same order. As such, we'll just store the draw state in a deque rather
   // than trying to perform any kind of matching with the requests.
@@ -388,7 +391,8 @@ MaterialManager::MaterialKey Renderable::SetMaterialInstance(
     MaterialManager::MaterialKey key) {
   MaterialManager::MaterialKey prev = curr_state_.material_key;
   if (key != curr_state_.material_key) {
-    filament::MaterialInstance* instance = material_mgr_->GetInstance(key);
+    const filament::MaterialInstance* instance =
+        material_mgr_->GetInstance(key);
     filament::RenderableManager& rm = GetEngine()->getRenderableManager();
     for (Part& part : parts_) {
       filament::RenderableManager::Instance ri = rm.getInstance(part.entity);