From 8d2154af26446963ea349e855218989a3d4b577d Mon Sep 17 00:00:00 2001
From: Tommy Walton <82672795+amzn-tommy@users.noreply.github.com>
Date: Wed, 30 Jun 2021 11:13:54 -0700
Subject: [PATCH] Partial fix for LYN-2227 : MeshComponent initialization
 performance improvement (#1381)

Skip a shader item before creating a shader instance if it's not going to be rendered based on the draw tag. This avoids creating and releasing the shader instance over and over again, which results in a disk write each time during release.
---
 .../Code/Source/RPI.Public/MeshDrawPacket.cpp | 51 +++++++++++++------
 1 file changed, 36 insertions(+), 15 deletions(-)

diff --git a/Gems/Atom/RPI/Code/Source/RPI.Public/MeshDrawPacket.cpp b/Gems/Atom/RPI/Code/Source/RPI.Public/MeshDrawPacket.cpp
index b29fb6d38d..8a402b5546 100644
--- a/Gems/Atom/RPI/Code/Source/RPI.Public/MeshDrawPacket.cpp
+++ b/Gems/Atom/RPI/Code/Source/RPI.Public/MeshDrawPacket.cpp
@@ -12,6 +12,7 @@
 #include <Atom/RPI.Public/Scene.h> 
 #include <Atom/RPI.Reflect/Material/MaterialFunctor.h>
 #include <Atom/RHI/DrawPacketBuilder.h>
+#include <Atom/RHI/RHISystemInterface.h>
 #include <AzCore/Console/Console.h>
 
 namespace AZ
@@ -154,6 +155,40 @@ namespace AZ
             auto appendShader = [&](const ShaderCollection::Item& shaderItem)
             {
                 AZ_PROFILE_SCOPE(Debug::ProfileCategory::AzRender, "appendShader()");
+
+                // Skip the shader item without creating the shader instance
+                // if the mesh is not going to be rendered based on the draw tag
+                RHI::RHISystemInterface* rhiSystem = RHI::RHISystemInterface::Get();
+                RHI::DrawListTagRegistry* drawListTagRegistry = rhiSystem->GetDrawListTagRegistry();
+
+                // Use the explicit draw list override if exists.
+                RHI::DrawListTag drawListTag = shaderItem.GetDrawListTagOverride();
+
+                if (drawListTag.IsNull())
+                {
+                    Data::Asset<RPI::ShaderAsset> shaderAsset = shaderItem.GetShaderAsset();
+                    if (!shaderAsset.IsReady())
+                    {
+                        // The shader asset needs to be loaded before we can check the draw tag.
+                        // If it's not loaded yet, the instance database will do a blocking load
+                        // when we create the instance below, so might as well load it now.
+                        shaderAsset.QueueLoad();
+
+                        if (shaderAsset.IsLoading())
+                        {
+                            shaderAsset.BlockUntilLoadComplete();
+                        }
+                    }
+
+                    drawListTag = drawListTagRegistry->FindTag(shaderAsset->GetDrawListName());
+                }
+
+                if (!parentScene.HasOutputForPipelineState(drawListTag))
+                {
+                    // drawListTag not found in this scene, so don't render this item
+                    return false;
+                }
+
                 Data::Instance<Shader> shader = RPI::Shader::FindOrCreate(shaderItem.GetShaderAsset());
                 if (!shader)
                 {
@@ -244,21 +279,7 @@ namespace AZ
                     drawSrg->Compile();
                 }
 
-                // Use the default draw list tag from the shader variant.
-                RHI::DrawListTag drawListTag = shader->GetDrawListTag();
-
-                // Use the explicit draw list override if exist.
-                RHI::DrawListTag runtimeTag = shaderItem.GetDrawListTagOverride();
-                if (!runtimeTag.IsNull())
-                {
-                    drawListTag = runtimeTag;
-                }
-
-                if (!parentScene.ConfigurePipelineState(drawListTag, pipelineStateDescriptor))
-                {
-                    // drawListTag not found in this scene, so don't render this item
-                    return false;
-                }
+                parentScene.ConfigurePipelineState(drawListTag, pipelineStateDescriptor);
 
                 const RHI::PipelineState* pipelineState = shader->AcquirePipelineState(pipelineStateDescriptor);
                 if (!pipelineState)