Pick face 2505.1 mesh info index v2

Gems/Atom/Feature/Common/Code/Include/Atom/Feature/Mesh/MeshFeatureProcessorInterface.h

@@ -132,6 +132,9 @@ namespace AZ
             virtual void ConnectMeshDrawPacketUpdatedHandler(MeshDrawPacketUpdatedEvent::Handler& handler) = 0;
 
             virtual CustomMaterialInfo GetCustomMaterialWithFallback(const CustomMaterialId& id) const = 0;
+
+            //! Returns lodIndex * 32 + meshIndex, the value placed in DrawSrg::m_meshInfoIndex per draw call.
+            virtual int32_t GetMeshInfoIndex(size_t modelLodIndex, size_t meshIndex) const = 0;
         };
 
         using CustomMaterialMap = AZStd::unordered_map<CustomMaterialId, CustomMaterialInfo>;

Gems/Atom/Feature/Common/Code/Source/Mesh/MeshFeatureProcessor.cpp

@@ -2197,7 +2197,13 @@ namespace AZ
                 if (!r_meshInstancingEnabled || instanceGroupInsertResult.m_instanceCount == 1)
                 {
                     // setup the mesh draw packet
-                    RPI::MeshDrawPacket drawPacket(modelLod, meshIndex, material, meshObjectSrg, customMaterialInfo.m_uvMapping);
+                    RPI::MeshDrawPacket drawPacket(
+                        modelLod,
+                        meshIndex,
+                        GetMeshInfoIndex(modelLodIndex, meshIndex),
+                        material,
+                        meshObjectSrg,
+                        customMaterialInfo.m_uvMapping);
 
                     // set the shader option to select forward pass IBL specular if necessary
                     if (!drawPacket.SetShaderOption(s_o_meshUseForwardPassIBLSpecular_Name, AZ::RPI::ShaderOptionValue{ m_descriptor.m_useForwardPassIblSpecular }))
@@ -3146,5 +3152,15 @@ namespace AZ
             handler.Connect(m_meshDrawPacketUpdatedEvent);
         }
 
+        int32_t ModelDataInstance::GetMeshInfoIndex(size_t modelLodIndex, size_t meshIndex) const
+        {
+            // Simplified version of the function from PR #19123
+            // Indexes all submeshes in a globally unique way.
+            static constexpr uint32_t MeshInfoIndexMeshesPerLod = 32;
+            static constexpr uint32_t MeshInfoIndicesPerMesh = MeshInfoIndexMeshesPerLod * RPI::ModelLodAsset::LodCountMax;
+            return static_cast<int32_t>(
+                m_objectId.GetIndex() * MeshInfoIndicesPerMesh + modelLodIndex * MeshInfoIndexMeshesPerLod + meshIndex);
+        }
+
     } // namespace Render
 } // namespace AZ

Gems/Atom/Feature/Common/Code/Source/Mesh/MeshFeatureProcessor.h

@@ -115,6 +115,7 @@ namespace AZ
             void BuildDrawPacketList(MeshFeatureProcessor* meshFeatureProcessor, size_t modelLodIndex);
             void SetRayTracingData(MeshFeatureProcessor* meshFeatureProcessor);
             void RemoveRayTracingData(RayTracingFeatureProcessor* rayTracingFeatureProcessor);
+            int32_t GetMeshInfoIndex(size_t modelLodIndex, size_t meshIndex) const override;
             void SetIrradianceData(
                 RayTracingFeatureProcessor::SubMesh& subMesh,
                 const Data::Instance<RPI::Material> material,

Gems/Atom/RPI/Assets/ShaderLib/Atom/RPI/ShaderResourceGroups/DefaultDrawSrg.azsli

@@ -28,6 +28,7 @@ ShaderResourceGroup DrawSrg : SRG_PerDraw
 {
     // This SRG is unique per draw packet
     uint m_uvStreamTangentBitmask;
+    uint m_meshInfoIndex;
 
 #if USE_DRAWSRG_MESHLOD_MESHINDEX
     // See MeshDrawPacket.h

Gems/Atom/RPI/Code/Include/Atom/RPI.Public/MeshDrawPacket.h

@@ -53,6 +53,7 @@ namespace AZ
             MeshDrawPacket(
                 ModelLod& modelLod,
                 size_t modelLodMeshIndex,
+                int32_t meshInfoIndex,
                 Data::Instance<Material> materialOverride,
                 Data::Instance<ShaderResourceGroup> objectSrg,
                 const MaterialModelUvOverrideMap& materialModelUvMap = {});
@@ -119,6 +120,9 @@ namespace AZ
             // The index of the mesh within m_modelLod that is represented by the DrawPacket
             size_t m_modelLodMeshIndex;
 
+            // Compact LOD-stable index: lodIndex * 32 + meshIndex. See ModelDataInstance::GetMeshInfoIndex.
+            int32_t m_meshInfoIndex = -1;
+
             // The per-object shader resource group
             Data::Instance<ShaderResourceGroup> m_objectSrg;
 

Gems/Atom/RPI/Code/Source/RPI.Public/MeshDrawPacket.cpp

@@ -34,12 +34,14 @@ namespace AZ
         MeshDrawPacket::MeshDrawPacket(
             ModelLod& modelLod,
             size_t modelLodMeshIndex,
+            int32_t meshInfoIndex,
             Data::Instance<Material> materialOverride,
             Data::Instance<ShaderResourceGroup> objectSrg,
             const MaterialModelUvOverrideMap& materialModelUvMap
         )
             : m_modelLod(&modelLod)
             , m_modelLodMeshIndex(modelLodMeshIndex)
+            , m_meshInfoIndex(meshInfoIndex)
             , m_objectSrg(objectSrg)
             , m_material(materialOverride)
             , m_materialModelUvMap(materialModelUvMap)
@@ -441,6 +443,16 @@ namespace AZ
                         drawSrg->SetConstant(index, aznumeric_cast<uint32_t>(m_modelLodMeshIndex));
                     }
 
+                    if (m_meshInfoIndex >= 0)
+                    {
+                        AZ::Name meshInfoNameIdx("m_meshInfoIndex");
+                        auto meshInfoConstIdx = drawSrg->FindShaderInputConstantIndex(meshInfoNameIdx);
+                        if (meshInfoConstIdx.IsValid())
+                        {
+                            drawSrg->SetConstant(meshInfoConstIdx, aznumeric_cast<uint32_t>(m_meshInfoIndex));
+                        }
+                    }
+
                     // TODO: Does it make sense to call Compile() in the case where both SetConstant() calls above fail?
                     // Leaving it as always calling Compile() as precaution that there's code somewhere else that assumes
                     // Compile() was already called on DrawSrg.