From c84578c37f6846d42ffc39b4bdb2100920be3011 Mon Sep 17 00:00:00 2001
From: Chris Santora <santorac@amazon.com>
Date: Sun, 16 May 2021 17:54:21 -0700
Subject: [PATCH] Optimized a bit by skipping layers when the blend weight is
 0. This reduced frame time by about 2ms (from 12ms when parallax was off, and
 from 47ms when parallax was on).

---
 .../StandardMultilayerPBR_ForwardPass.azsl    | 22 ++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/Gems/Atom/Feature/Common/Assets/Materials/Types/StandardMultilayerPBR_ForwardPass.azsl b/Gems/Atom/Feature/Common/Assets/Materials/Types/StandardMultilayerPBR_ForwardPass.azsl
index 1fed3acbee..88a3ca29c0 100644
--- a/Gems/Atom/Feature/Common/Assets/Materials/Types/StandardMultilayerPBR_ForwardPass.azsl
+++ b/Gems/Atom/Feature/Common/Assets/Materials/Types/StandardMultilayerPBR_ForwardPass.azsl
@@ -386,16 +386,22 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
     // ------- Layer 1 (base layer) -----------
 
     ProcessedMaterialInputs lightingInputLayer1;
+    if(blendWeights.r > 0)
     {
         StandardMaterialInputs inputs;
         FILL_STANDARD_MATERIAL_INPUTS(inputs, MaterialSrg::m_layer1_, o_layer1_, blendWeights.r)
         lightingInputLayer1 = ProcessStandardMaterialInputs(inputs);
     }
+    else
+    {
+        lightingInputLayer1.InitializeToZero();
+        blendWeights.r = 0;
+    }
     
     // ----------- Layer 2 -----------
 
     ProcessedMaterialInputs lightingInputLayer2; 
-    if(o_layer2_enabled)
+    if(o_layer2_enabled && blendWeights.g > 0)
     {
         StandardMaterialInputs inputs;
         FILL_STANDARD_MATERIAL_INPUTS(inputs, MaterialSrg::m_layer2_, o_layer2_, blendWeights.g)
@@ -404,12 +410,13 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
     else
     {
         lightingInputLayer2.InitializeToZero();
+        blendWeights.g = 0;
     }
     
     // ----------- Layer 3 -----------
 
     ProcessedMaterialInputs lightingInputLayer3;
-    if(o_layer3_enabled)
+    if(o_layer3_enabled && blendWeights.b > 0)
     {
         StandardMaterialInputs inputs;
         FILL_STANDARD_MATERIAL_INPUTS(inputs, MaterialSrg::m_layer3_, o_layer3_, blendWeights.b)
@@ -418,6 +425,7 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
     else
     {
         lightingInputLayer3.InitializeToZero();
+        blendWeights.b = 0;
     }
 
     // ------- Combine all layers ---------
@@ -428,12 +436,16 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
 
     // ------- Combine Normals ---------
 
-    float3 normalTS = lightingInputLayer1.m_normalTS;
-    if(o_layer2_enabled)
+    float3 normalTS = float3(0,0,1);
+    if(blendWeights.r > 0)
+    {
+        normalTS = lightingInputLayer1.m_normalTS;
+    }
+    if(o_layer2_enabled && blendWeights.g > 0)
     {
         normalTS = ReorientTangentSpaceNormal(normalTS, lightingInputLayer2.m_normalTS);
     }
-    if(o_layer3_enabled)
+    if(o_layer3_enabled && blendWeights.b > 0)
     {
         normalTS = ReorientTangentSpaceNormal(normalTS, lightingInputLayer3.m_normalTS);
     }