Fix sky, skylight and reflections banding artifacts with a random noise

#3254 #3318

Source/Engine/Level/Actors/Sky.cpp

@@ -24,7 +24,7 @@ GPU_CB_STRUCT(Data {
     Matrix WorldViewProjection;
     Matrix InvViewProjection;
     Float3 ViewOffset;
-    float Padding;
+    float NoiseScale;
     ShaderGBufferData GBuffer;
     ShaderAtmosphericFogData Fog;
     });
@@ -184,6 +184,7 @@ void Sky::ApplySky(GPUContext* context, RenderContext& renderContext, const Matr
     Matrix::Transpose(renderContext.View.IVP, data.InvViewProjection);
     GBufferPass::SetInputs(renderContext.View, data.GBuffer);
     data.ViewOffset = renderContext.View.Origin + GetPosition();
+    data.NoiseScale = renderContext.View.IsSingleFrame ? 0.01f : 0.03f;
     InitConfig(data.Fog);
     //data.Fog.AtmosphericFogSunPower *= SunLight ? SunLight->Brightness : 1.0f;
     if (EnumHasNoneFlags(renderContext.View.Flags, ViewFlags::SpecularLight))

Source/Shaders/Lights.shader

@@ -8,6 +8,7 @@
 #include "./Flax/IESProfile.hlsl"
 #include "./Flax/GBuffer.hlsl"
 #include "./Flax/Lighting.hlsl"
+#include "./Flax/Noise.hlsl"
 
 // Per light data
 META_CB_BEGIN(0, PerLight)
@@ -168,6 +169,9 @@ float4 PS_Sky(Model_VS2PS input) : SV_Target0
 	if (gBuffer.ShadingModel != SHADING_MODEL_UNLIT)
 	{
 		output = GetSkyLightLighting(Light, gBuffer, CubeImage);
+
+        // Apply dithering to hide banding artifacts
+        output.rgb += rand2dTo1d(uv) * 0.02f * Luminance(saturate(output.rgb));
 	}
 
 	return output;

Source/Shaders/Reflections.shader

@@ -4,6 +4,7 @@
 #include "./Flax/MaterialCommon.hlsl"
 #include "./Flax/BRDF.hlsl"
 #include "./Flax/Random.hlsl"
+#include "./Flax/Noise.hlsl"
 #include "./Flax/MonteCarlo.hlsl"
 #include "./Flax/LightingCommon.hlsl"
 #include "./Flax/GBuffer.hlsl"
@@ -55,7 +56,12 @@ float4 PS_EnvProbe(Model_VS2PS input) : SV_Target0
 	}
 
 	// Sample probe
-	return SampleReflectionProbe(gBufferData.ViewPos, Probe, PData, gBuffer.WorldPos, gBuffer.Normal, gBuffer.Roughness);
+	float4 color = SampleReflectionProbe(gBufferData.ViewPos, Probe, PData, gBuffer.WorldPos, gBuffer.Normal, gBuffer.Roughness);
+
+    // Apply dithering to hide banding artifacts
+    color.rgb += rand2dTo1d(uv) * 0.02f * Luminance(saturate(color.rgb));
+
+    return color;
 }
 
 // Pixel Shader for reflections combine pass (additive rendering to the light buffer)

Source/Shaders/Sky.shader

@@ -4,13 +4,14 @@
 #include "./Flax/MaterialCommon.hlsl"
 #include "./Flax/GBuffer.hlsl"
 #include "./Flax/Common.hlsl"
+#include "./Flax/Noise.hlsl"
 #include "./Flax/AtmosphereFog.hlsl"
 
 META_CB_BEGIN(0, Data)
 float4x4 WorldViewProjection;
 float4x4 InvViewProjection;
 float3 ViewOffset;
-float Padding;
+float NoiseScale;
 GBufferData GBuffer;
 AtmosphericFogData AtmosphericFog;
 META_CB_END
@@ -53,6 +54,11 @@ GBufferOutput PS_Sky(MaterialInput input)
 	// Sample atmosphere color
     float4 color = GetAtmosphericFog(AtmosphericFog, gBufferData.ViewFar, gBufferData.ViewPos + ViewOffset, viewVector, gBufferData.ViewFar, float3(0, 0, 0));
 
+    // Apply dithering to hide banding artifacts
+    float2 uv = (input.ScreenPos.xy / input.ScreenPos.w) * float2(0.5, -0.5) + float2(0.5, 0.5);
+    float luminance = Luminance(saturate(color.rgb));
+    color.rgb += rand2dTo1d(uv) * luminance * NoiseScale;
+
 	// Pack GBuffer
 	output.Light = color;
 	output.RT0 = float4(0, 0, 0, 0);