From 3696501050f48f5637cd5c86706fcaeaeb402f4e Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Fri, 29 Mar 2024 18:07:10 +0100
Subject: [PATCH] Fix invalid shader codegen when using `ddx`/`ddy` in material
 vertex shader

#2376
---
 .../MaterialGenerator.Material.cpp            | 24 +++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp b/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
index 508417895..66d24d4f3 100644
--- a/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
+++ b/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
@@ -421,15 +421,31 @@ void MaterialGenerator::ProcessGroupMaterial(Box* box, Node* node, Value& value)
     // DDX
     case 30:
     {
-        const auto inValue = tryGetValue(node->GetBox(0), 0, Value::Zero);
-        value = writeLocal(inValue.Type, String::Format(TEXT("ddx({0})"), inValue.Value), node);
+        if (_treeType == MaterialTreeType::PixelShader)
+        {
+            const auto inValue = tryGetValue(node->GetBox(0), 0, Value::Zero);
+            value = writeLocal(inValue.Type, String::Format(TEXT("ddx({0})"), inValue.Value), node);
+        }
+        else
+        {
+            // No derivatives support in VS/DS
+            value = Value::Zero;
+        }
         break;
     }
     // DDY
     case 31:
     {
-        const auto inValue = tryGetValue(node->GetBox(0), 0, Value::Zero);
-        value = writeLocal(inValue.Type, String::Format(TEXT("ddy({0})"), inValue.Value), node);
+        if (_treeType == MaterialTreeType::PixelShader)
+        {
+            const auto inValue = tryGetValue(node->GetBox(0), 0, Value::Zero);
+            value = writeLocal(inValue.Type, String::Format(TEXT("ddy({0})"), inValue.Value), node);
+        }
+        else
+        {
+            // No derivatives support in VS/DS
+            value = Value::Zero;
+        }
         break;
     }
     // Sign