From 92f4327fc2ea0a1a4d3512164af98ebe1dcd8187 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Sat, 20 Sep 2025 00:13:52 +0200
Subject: [PATCH] Fix missing volumetric fog affecting transparent materials

#3436
---
 Source/Engine/Graphics/Materials/MaterialShader.h      |  2 +-
 .../Graphics/Materials/MaterialShaderFeatures.cpp      | 10 ++++++++++
 .../Engine/Graphics/Materials/MaterialShaderFeatures.h |  2 +-
 Source/Shaders/ExponentialHeightFog.hlsl               |  5 +++++
 Source/Shaders/Fog.shader                              |  2 +-
 5 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Source/Engine/Graphics/Materials/MaterialShader.h b/Source/Engine/Graphics/Materials/MaterialShader.h
index aedf2e870..117246671 100644
--- a/Source/Engine/Graphics/Materials/MaterialShader.h
+++ b/Source/Engine/Graphics/Materials/MaterialShader.h
@@ -10,7 +10,7 @@
 /// <summary>
 /// Current materials shader version.
 /// </summary>
-#define MATERIAL_GRAPH_VERSION 174
+#define MATERIAL_GRAPH_VERSION 175
 
 class Material;
 class GPUShader;
diff --git a/Source/Engine/Graphics/Materials/MaterialShaderFeatures.cpp b/Source/Engine/Graphics/Materials/MaterialShaderFeatures.cpp
index 0dae6c93e..a140fb577 100644
--- a/Source/Engine/Graphics/Materials/MaterialShaderFeatures.cpp
+++ b/Source/Engine/Graphics/Materials/MaterialShaderFeatures.cpp
@@ -2,6 +2,7 @@
 
 #include "MaterialShaderFeatures.h"
 #include "Engine/Graphics/RenderTask.h"
+#include "Engine/Graphics/RenderBuffers.h"
 #include "Engine/Graphics/Textures/GPUTexture.h"
 #include "Engine/Renderer/RenderList.h"
 #include "Engine/Renderer/ShadowsPass.h"
@@ -24,18 +25,27 @@ void ForwardShadingFeature::Bind(MaterialShader::BindParameters& params, Span<by
     const int32 skyLightShaderRegisterIndex = srv + 1;
     const int32 shadowsBufferRegisterIndex = srv + 2;
     const int32 shadowMapShaderRegisterIndex = srv + 3;
+    const int32 volumetricFogTextureRegisterIndex = srv + 4;
     const bool canUseShadow = view.Pass != DrawPass::Depth;
 
     // Set fog input
+    GPUTextureView* volumetricFogTexture = nullptr;
     if (cache->Fog)
     {
         cache->Fog->GetExponentialHeightFogData(view, data.ExponentialHeightFog);
+        VolumetricFogOptions volumetricFog;
+        cache->Fog->GetVolumetricFogOptions(volumetricFog);
+        if (volumetricFog.UseVolumetricFog() && params.RenderContext.Buffers->VolumetricFog)
+            volumetricFogTexture = params.RenderContext.Buffers->VolumetricFog->ViewVolume();
+        else
+            data.ExponentialHeightFog.VolumetricFogMaxDistance = -1.0f;
     }
     else
     {
         data.ExponentialHeightFog.FogMinOpacity = 1.0f;
         data.ExponentialHeightFog.ApplyDirectionalInscattering = 0.0f;
     }
+    params.GPUContext->BindSR(volumetricFogTextureRegisterIndex, volumetricFogTexture);
 
     // Set directional light input
     if (cache->DirectionalLights.HasItems())
diff --git a/Source/Engine/Graphics/Materials/MaterialShaderFeatures.h b/Source/Engine/Graphics/Materials/MaterialShaderFeatures.h
index 25689e765..54b91af23 100644
--- a/Source/Engine/Graphics/Materials/MaterialShaderFeatures.h
+++ b/Source/Engine/Graphics/Materials/MaterialShaderFeatures.h
@@ -25,7 +25,7 @@ struct ForwardShadingFeature : MaterialShaderFeature
 {
     enum { MaxLocalLights = 4 };
 
-    enum { SRVs = 4 };
+    enum { SRVs = 5 };
 
     PACK_STRUCT(struct Data
         {
diff --git a/Source/Shaders/ExponentialHeightFog.hlsl b/Source/Shaders/ExponentialHeightFog.hlsl
index f6fb918f5..b5af721d8 100644
--- a/Source/Shaders/ExponentialHeightFog.hlsl
+++ b/Source/Shaders/ExponentialHeightFog.hlsl
@@ -92,4 +92,9 @@ float4 GetExponentialHeightFog(ExponentialHeightFogData exponentialHeightFog, fl
     return GetExponentialHeightFog(exponentialHeightFog, posWS, camWS, skipDistance, distance(posWS, camWS));
 }
 
+float4 CombineVolumetricFog(float4 fog, float4 volumetricFog)
+{
+    return float4(volumetricFog.rgb + fog.rgb * volumetricFog.a, volumetricFog.a * fog.a);
+}
+
 #endif
diff --git a/Source/Shaders/Fog.shader b/Source/Shaders/Fog.shader
index dfea921cc..5c4344688 100644
--- a/Source/Shaders/Fog.shader
+++ b/Source/Shaders/Fog.shader
@@ -63,7 +63,7 @@ float4 PS_Fog(Quad_VS2PS input) : SV_Target0
 #if VOLUMETRIC_FOG
     // Sample volumetric fog and mix it in
 	float4 volumetricFog = IntegratedLightScattering.SampleLevel(SamplerLinearClamp, volumeUV, 0);
-	fog = float4(volumetricFog.rgb + fog.rgb * volumetricFog.a, volumetricFog.a * fog.a);
+	fog = CombineVolumetricFog(fog, volumetricFog);
 #endif
 
 	return fog;