From c22f8e3607cc01f53af0605132e076eabfe6bd23 Mon Sep 17 00:00:00 2001
From: Gary M <exkage@yahoo.com>
Date: Fri, 31 May 2024 18:38:38 -0700
Subject: [PATCH] Initial AGX Impl

---
 Source/Engine/Graphics/PostProcessSettings.h |  5 ++
 Source/Shaders/ColorGrading.shader           | 58 ++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/Source/Engine/Graphics/PostProcessSettings.h b/Source/Engine/Graphics/PostProcessSettings.h
index 525da3f36..4f3e4e080 100644
--- a/Source/Engine/Graphics/PostProcessSettings.h
+++ b/Source/Engine/Graphics/PostProcessSettings.h
@@ -52,6 +52,11 @@ API_ENUM() enum class ToneMappingMode
     /// The ACES Filmic reference tonemapper (approximation).
     /// </summary>
     ACES = 2,
+
+    /// <summary>
+    /// The AGX tonemapper.
+    /// </summary>
+    AGX = 3,
 };
 
 /// <summary>
diff --git a/Source/Shaders/ColorGrading.shader b/Source/Shaders/ColorGrading.shader
index ae4067b18..eea9c59e3 100644
--- a/Source/Shaders/ColorGrading.shader
+++ b/Source/Shaders/ColorGrading.shader
@@ -191,6 +191,60 @@ float3 TonemapACES(float3 linearColor)
 	return saturate(color);
 }
 
+#ifdef TONE_MAPPING_MODE_AGX
+
+float3 agxAscCdl(float3 color, float3 slope, float3 offset, float3 power, float sat) {
+    const float3 lw = float3(0.2126, 0.7152, 0.0722);
+    float luma = dot(color, lw);
+    float3 c = pow(color * slope + offset, power);
+    return luma + sat * (c - luma);
+}
+
+float3 TonemapAGX(float3 linearColor)
+{
+    static const float3x3 AgXInsetMatrix = {
+        0.8566, 0.1373, 0.1119,
+        0.0951, 0.7612, 0.0768,
+        0.0483, 0.1014, 0.8113
+    };
+
+    static const float3x3 AgXOutsetMatrix = {
+        1.1271, -0.1413, -0.1413,
+        -0.1106, 1.1578, -0.1106,
+        -0.0165, -0.0165, 1.2519
+    };
+
+    static const float AgxMinEv = -12.47393;
+    static const float AgxMaxEv = 4.026069;
+
+	float3 color = linearColor;
+    color = mul(color, AgXInsetMatrix);
+    color = max(color, 1e-10);
+    color = clamp(log2(color), AgxMinEv, AgxMaxEv);
+    color = (color - AgxMinEv) / (AgxMaxEv - AgxMinEv);
+
+    color = clamp(color, 0.0, 1.0);
+
+    float3 x2 = color * color;
+    float3 x4 = x2 * x2;    
+
+    color = + 15.5      * x4 * x2
+            - 40.14     * x4 * color
+            + 31.96     * x4
+            - 6.868     * x2 * color
+            + 0.4298    * x2
+            + 0.1191    * color
+            - 0.00232;
+
+    color = agxAscCdl(color, float3(1.0, 1.0, 1.0), float3(0.0, 0.0, 0.0), float3(1.35, 1.35, 1.35), 1.4);
+
+    color = mul(color, AgXOutsetMatrix);
+
+    color = clamp(color, 0.0, 1.0);
+
+	return color;
+}
+
 #endif
 
 // Perfoms the tonemapping on the input linear color
@@ -202,6 +256,8 @@ float3 Tonemap(float3 linearColor)
 	return TonemapNeutral(linearColor);
 #elif defined(TONE_MAPPING_MODE_ACES)
 	return TonemapACES(linearColor);
+#elif defined(TONE_MAPPING_MODE_AGX)
+    return TonemapAGX(linearColor);
 #else
 	return float3(0, 0, 0);
 #endif
@@ -292,6 +348,7 @@ META_PS(true, FEATURE_LEVEL_ES2)
 META_PERMUTATION_1(TONE_MAPPING_MODE_NONE=1)
 META_PERMUTATION_1(TONE_MAPPING_MODE_NEUTRAL=1)
 META_PERMUTATION_1(TONE_MAPPING_MODE_ACES=1)
+META_PERMUTATION_1(TONE_MAPPING_MODE_AGX=1)
 float4 PS_Lut2D(Quad_VS2PS input) : SV_Target
 {
 	return CombineLUTs(input.TexCoord, 0);
@@ -301,6 +358,7 @@ META_PS(true, FEATURE_LEVEL_ES2)
 META_PERMUTATION_1(TONE_MAPPING_MODE_NONE=1)
 META_PERMUTATION_1(TONE_MAPPING_MODE_NEUTRAL=1)
 META_PERMUTATION_1(TONE_MAPPING_MODE_ACES=1)
+META_PERMUTATION_1(TONE_MAPPING_MODE_AGX=1)
 float4 PS_Lut3D(Quad_GS2PS input) : SV_Target
 {
 	return CombineLUTs(input.Vertex.TexCoord, input.LayerIndex);