Fixed an issue with Actors where the material slot IDs were incorrect, and caused the displayed slot labels to be all "<unknown>" (and likely other issues).

Signed-off-by: santorac <55155825+santorac@users.noreply.github.com>

Gems/Atom/Feature/Common/Code/Include/Atom/Feature/SkinnedMesh/SkinnedMeshInputBuffers.h

@@ -45,7 +45,7 @@ namespace AZ
             uint32_t m_vertexOffset = 0;
             uint32_t m_vertexCount = 0;
             Aabb m_aabb = Aabb::CreateNull();
-            Data::Asset<RPI::MaterialAsset> m_material;
+            AZ::RPI::ModelMaterialSlot m_materialSlot;
         };
 
         //! Buffer views for a specific sub-mesh that are not modified during skinning and thus are shared by all instances of the same skinned mesh

Gems/Atom/Feature/Common/Code/Source/SkinnedMesh/SkinnedMeshInputBuffers.cpp

@@ -640,12 +640,7 @@ namespace AZ
                     Aabb localAabb = lod.m_subMeshProperties[i].m_aabb;
                     modelLodCreator.SetMeshAabb(AZStd::move(localAabb));
                     
-                    // Create a separate material slot for each sub-mesh
-                    AZ::RPI::ModelMaterialSlot materialSlot;
-                    materialSlot.m_stableId = i;
-                    materialSlot.m_defaultMaterialAsset = lod.m_subMeshProperties[i].m_material;
-
-                    modelLodCreator.SetMeshMaterialSlot(materialSlot);
+                    modelLodCreator.SetMeshMaterialSlot(lod.m_subMeshProperties[i].m_materialSlot);
 
                     modelLodCreator.EndMesh();
                 }

Gems/AtomLyIntegration/EMotionFXAtom/Code/Source/ActorAsset.cpp

@@ -96,9 +96,10 @@ namespace AZ
                         skinnedSubMesh.m_vertexCount = aznumeric_cast<uint32_t>(subMeshVertexCount);
                         lodVertexCount += aznumeric_cast<uint32_t>(subMeshVertexCount);
 
-                        skinnedSubMesh.m_material = lodAsset->GetMaterialSlot(modelMesh.GetMaterialSlotIndex()).m_defaultMaterialAsset;
+                        skinnedSubMesh.m_materialSlot = lodAsset->GetMaterialSlot(modelMesh.GetMaterialSlotIndex());
+
                         // Queue the material asset - the ModelLod seems to handle delayed material loads
-                        skinnedSubMesh.m_material.QueueLoad();
+                        skinnedSubMesh.m_materialSlot.m_defaultMaterialAsset.QueueLoad();
 
                         subMeshes.push_back(skinnedSubMesh);
                     }

Gems/AtomLyIntegration/EMotionFXAtom/Code/Source/AtomActorInstance.cpp

@@ -503,16 +503,18 @@ namespace AZ
                     const AZStd::vector< SkinnedSubMeshProperties>& subMeshProperties = inputLod.GetSubMeshProperties();
                     for (const SkinnedSubMeshProperties& submesh : subMeshProperties)
                     {
-                        AZ_Error("AtomActorInstance", submesh.m_material, "Actor does not have a valid default material in lod %d", lodIndex);
-                        if (submesh.m_material)
+                        Data::Asset<RPI::MaterialAsset> materialAsset = submesh.m_materialSlot.m_defaultMaterialAsset;
+                        AZ_Error("AtomActorInstance", materialAsset, "Actor does not have a valid default material in lod %d", lodIndex);
+
+                        if (materialAsset)
                         {
-                            if (!submesh.m_material->IsReady())
+                            if (!materialAsset->IsReady())
                             {
                                 // Start listening for the material's OnAssetReady event.
                                 // AtomActorInstance::Create is called on the main thread, so there should be no need to synchronize with the OnAssetReady event handler
                                 // since those events will also come from the main thread
-                                m_waitForMaterialLoadIds.insert(submesh.m_material->GetId());
-                                Data::AssetBus::MultiHandler::BusConnect(submesh.m_material->GetId());
+                                m_waitForMaterialLoadIds.insert(materialAsset->GetId());
+                                Data::AssetBus::MultiHandler::BusConnect(materialAsset->GetId());
                             }
                         }
                     }