Improve DDGI quality

Source/Engine/Renderer/GI/DynamicDiffuseGlobalIllumination.cpp

@@ -462,7 +462,7 @@ bool DynamicDiffuseGlobalIlluminationPass::Render(RenderContext& renderContext,
             ddgiData.Result.Constants.ProbesScrollOffsets[cascadeIndex] = Int4(cascade.ProbeScrollOffsets, 0);
         }
         ddgiData.Result.Constants.RayMaxDistance = 10000.0f; // TODO: adjust to match perf/quality ratio (make it based on Global SDF and Global Surface Atlas distance)
-        ddgiData.Result.Constants.ViewDir = renderContext.View.Direction;
+        ddgiData.Result.Constants.ViewPos = renderContext.View.Position;
         ddgiData.Result.Constants.RaysCount = probeRaysCount;
         ddgiData.Result.Constants.ProbeHistoryWeight = probeHistoryWeight;
         ddgiData.Result.Constants.IrradianceGamma = 5.0f;

Source/Engine/Renderer/GI/DynamicDiffuseGlobalIllumination.h

@@ -24,7 +24,7 @@ public:
         float RayMaxDistance;
         float IndirectLightingIntensity;
         Float4 RaysRotation;
-        Float3 ViewDir;
+        Float3 ViewPos;
         uint32 RaysCount;
         Float3 FallbackIrradiance;
         float Padding0;

Source/Shaders/GI/DDGI.hlsl

@@ -32,7 +32,7 @@ struct DDGIData
     float RayMaxDistance;
     float IndirectLightingIntensity;
     float4 RaysRotation;
-    float3 ViewDir;
+    float3 ViewPos;
     uint RaysCount;
     float3 FallbackIrradiance;
     float Padding0;
@@ -120,8 +120,9 @@ float2 GetDDGIProbeUV(DDGIData data, uint cascadeIndex, uint probeIndex, float2
 }
 
 // Samples DDGI probes volume at the given world-space position and returns the irradiance.
-// rand - randomized per-pixel value in range 0-1, used to smooth dithering for cascades blending
+// bias - scales the bias vector to the initial sample point to reduce self-shading artifacts
-float3 SampleDDGIIrradiance(DDGIData data, Texture2D<snorm float4> probesState, Texture2D<float4> probesDistance, Texture2D<float4> probesIrradiance, float3 worldPosition, float3 worldNormal, float bias, float dither = 0.0f)
+// dither - randomized per-pixel value in range 0-1, used to smooth dithering for cascades blending
+float3 SampleDDGIIrradiance(DDGIData data, Texture2D<snorm float4> probesState, Texture2D<float4> probesDistance, Texture2D<float4> probesIrradiance, float3 worldPosition, float3 worldNormal, float bias = 0.2f, float dither = 0.0f)
 {
     // Select the highest cascade that contains the sample location
     uint cascadeIndex = 0;
@@ -163,7 +164,8 @@ float3 SampleDDGIIrradiance(DDGIData data, Texture2D<snorm float4> probesState,
     float3 probesExtent = (data.ProbesCounts - 1) * (probesSpacing * 0.5f);
 
     // Bias the world-space position to reduce artifacts
-    float3 surfaceBias = (worldNormal * bias) + (data.ViewDir * (bias * -4.0f));
+    float3 viewDir = normalize(data.ViewPos - worldPosition);
+    float3 surfaceBias = (worldNormal * 0.2f + viewDir * 0.8f) * (0.75f * probesSpacing * bias);
     float3 biasedWorldPosition = worldPosition + surfaceBias;
 
     // Get the grid coordinates of the probe nearest the biased world position
@@ -190,7 +192,7 @@ float3 SampleDDGIIrradiance(DDGIData data, Texture2D<snorm float4> probesState,
         // Calculate the distance and direction from the (biased and non-biased) shading point and the probe
         float3 worldPosToProbe = normalize(probePosition - worldPosition);
         float3 biasedPosToProbe = normalize(probePosition - biasedWorldPosition);
-        float biasedPosToProbeDist = length(probePosition - biasedWorldPosition);
+        float biasedPosToProbeDist = length(probePosition - biasedWorldPosition) * 0.95f;
 
         // Smooth backface test
         float weight = Square(dot(worldPosToProbe, worldNormal) * 0.5f + 0.5f);

Source/Shaders/GI/DDGI.shader

@@ -387,7 +387,7 @@ void CS_UpdateProbes(uint3 GroupThreadId : SV_GroupThreadID, uint3 GroupId : SV_
     // Load current probe value
     float3 previous = RWOutput[outputCoords].rgb;
     bool wasActivated = GetProbeState(probeState, DDGI_PROBE_STATE_ACTIVATED);
-    if (wasActivated)
+    if (ResetBlend || wasActivated)
         previous = float3(0, 0, 0);
 
     // Blend current value with the previous probe data
@@ -522,7 +522,7 @@ void PS_IndirectLighting(Quad_VS2PS input, out float4 output : SV_Target0)
     }
 
     // Sample irradiance
-    float bias = 1.0f;
+    float bias = 0.2f;
     float dither = RandN2(input.TexCoord + TemporalTime).x;
     float3 irradiance = SampleDDGIIrradiance(DDGI, ProbesState, ProbesDistance, ProbesIrradiance, gBuffer.WorldPos, gBuffer.Normal, bias, dither);
     

Source/Shaders/GI/GlobalSurfaceAtlas.shader

@@ -125,7 +125,7 @@ float4 PS_Lighting(AtlasVertexOutput input) : SV_Target
 
     // Calculate lighting
     float3 diffuseColor = GetDiffuseColor(gBuffer);
-    diffuseColor = min(diffuseColor, 0.9f); // Nothing reflects diffuse like perfectly in the real world (ensure to have energy loss at each light bounce)
+    diffuseColor = min(diffuseColor, 0.98f); // Nothing reflects diffuse like perfectly in the real world (ensure to have energy loss at each light bounce)
     float3 diffuse = Diffuse_Lambert(diffuseColor);
     float4 light = float4(diffuse * irradiance * gBuffer.AO, 1);
 #else

Source/Shaders/VolumetricFog.shader

@@ -337,7 +337,7 @@ void CS_LightScattering(uint3 GroupId : SV_GroupID, uint3 DispatchThreadId : SV_
 
 #if USE_DDGI
         // Dynamic Diffuse Global Illumination
-        float3 irradiance = SampleDDGIIrradiance(DDGI, ProbesState, ProbesDistance, ProbesIrradiance, positionWS, cameraVectorNormalized, 1.0f);
+        float3 irradiance = SampleDDGIIrradiance(DDGI, ProbesState, ProbesDistance, ProbesIrradiance, positionWS, cameraVectorNormalized, 0.0f, cellOffset.x);
         lightScattering += float4(irradiance, 1);
 #else
 		// Sky light