Add temporal dithering and more accurate blending for contact shadows

Source/Engine/Level/Actors/Light.h

@@ -162,7 +162,7 @@ public:
     /// <summary>
     /// The length of the rays for contact shadows computed via the screen-space tracing. Set this to values higher than 0 to enable screen-space shadows rendering for this light. This improves the shadowing details. Actual ray distance is based on the pixel distance from the camera.
     /// </summary>
-    API_FIELD(Attributes="EditorOrder(99), EditorDisplay(\"Shadow\"), Limit(0.0f, 0.1f, 0.001f)")
+    API_FIELD(Attributes="EditorOrder(99), EditorDisplay(\"Shadow\"), Limit(0.0f, 0.4f, 0.001f)")
     float ContactShadowsLength = 0.0f;
 
     /// <summary>

Source/Engine/Renderer/ShadowsPass.cpp

@@ -34,7 +34,7 @@ GPU_CB_STRUCT(Data {
     ShaderLightData Light;
     Matrix WVP;
     Matrix ViewProjectionMatrix;
-    float Dummy0;
+    uint32 FrameIndexMod8;
     float TemporalTime;
     float ContactShadowsDistance;
     float ContactShadowsLength;
@@ -1718,6 +1718,7 @@ void ShadowsPass::RenderShadowMask(RenderContextBatch& renderContextBatch, Rende
     else if (light.IsSpotLight)
         ((RenderSpotLightData&)light).SetShaderData(sperLight.Light, true);
     Matrix::Transpose(view.ViewProjection(), sperLight.ViewProjectionMatrix);
+    sperLight.FrameIndexMod8 = renderContext.List->Setup.UseTemporalAAJitter ? (int32)(Engine::FrameCount % 8) : 0;
     sperLight.TemporalTime = renderContext.List->Setup.UseTemporalAAJitter ? RenderTools::ComputeTemporalTime() : 0.0f;
     sperLight.ContactShadowsDistance = light.ShadowsDistance;
     sperLight.ContactShadowsLength = EnumHasAnyFlags(view.Flags, ViewFlags::ContactShadows) ? light.ContactShadowsLength : 0.0f;

Source/Shaders/GI/DDGI.shader

@@ -863,7 +863,7 @@ void CS_UpdateProbes(uint3 GroupThreadId : SV_GroupThreadID, uint3 GroupId : SV_
     result = float4(lerp(result.rgb, previous.rgb, historyWeight), 1.0f);
 
     // Apply quantization error to reduce yellowish artifacts due to R11G11B10 format
-    float noise = InterleavedGradientNoise(octahedralCoords, FrameIndexMod8);
+    float noise = InterleavedGradientNoise(octahedralCoords * 10, FrameIndexMod8);
     result.rgb = QuantizeColor(result.rgb, noise, QuantizationError);
 #else
     result = float4(lerp(result.rg, previous.rg, historyWeight), 0.0f, 1.0f);

Source/Shaders/Shadows.shader

@@ -13,7 +13,7 @@ GBufferData GBuffer;
 LightData Light;
 float4x4 WVP;
 float4x4 ViewProjectionMatrix;
-float Dummy0;
+uint FrameIndexMod8;
 float TemporalTime;
 float ContactShadowsDistance;
 float ContactShadowsLength;
@@ -26,7 +26,9 @@ DECLARE_GBUFFERDATA_ACCESS(GBuffer)
 
 #if CONTACT_SHADOWS
 
-float RayCastScreenSpaceShadow(GBufferData gBufferData, GBufferSample gBuffer, float3 rayStartWS, float3 rayDirWS, float rayLength)
+#include "./Flax/Noise.hlsl"
+
+float RayCastScreenSpaceShadow(GBufferData gBufferData, GBufferSample gBuffer, float3 rayStartWS, float3 rayDirWS, float rayLength, float dither = 0.5f)
 {
     uint2 depthSize;
     Depth.GetDimensions(depthSize.x, depthSize.y);
@@ -53,7 +55,7 @@ float RayCastScreenSpaceShadow(GBufferData gBufferData, GBufferSample gBuffer, f
     float rayStepDstMin = min(rayStepDst.x, rayStepDst.y);
     float3 rayStepMin = raySize / max(min(maxSteps, rayStepDstMin), 1);
     float3 rayStep = raySize / maxSteps;
-    float3 ray = rayStart + rayStepMin * 1.5f;
+    float3 ray = rayStart + rayStepMin * (dither * 2 + 1.0f);
 
     // Sample over the ray
     float lightAmountMax = 0;
@@ -113,8 +115,10 @@ float4 PS_DirLight(Quad_VS2PS input) : SV_Target0
     ShadowSample shadow = SampleDirectionalLightShadow(Light, ShadowsBuffer, ShadowMap, gBuffer, TemporalTime);
 
 #if CONTACT_SHADOWS
-	// Calculate screen-space contact shadow
-	shadow.SurfaceShadow *= RayCastScreenSpaceShadow(gBufferData, gBuffer, gBuffer.WorldPos, Light.Direction, ContactShadowsLength);
+    // Calculate screen-space contact shadow
+    float dither = InterleavedGradientNoise(input.Position.xy, FrameIndexMod8);
+    float contactShadow = RayCastScreenSpaceShadow(gBufferData, gBuffer, gBuffer.WorldPos, Light.Direction, ContactShadowsLength, dither);
+    shadow.SurfaceShadow = min(shadow.SurfaceShadow, contactShadow);
 #endif
 
 	return GetShadowMask(shadow);
@@ -155,8 +159,10 @@ float4 PS_LocalLight(Model_VS2PS input) : SV_Target0
 #endif
 
 #if CONTACT_SHADOWS
-	// Calculate screen-space contact shadow
-	shadow.SurfaceShadow *= RayCastScreenSpaceShadow(gBufferData, gBuffer, gBuffer.WorldPos, normalize(Light.Position - gBuffer.WorldPos), ContactShadowsLength);
+    // Calculate screen-space contact shadow
+    float dither = InterleavedGradientNoise(input.ScreenPos.xy, FrameIndexMod8);
+    float contactShadow = RayCastScreenSpaceShadow(gBufferData, gBuffer, gBuffer.WorldPos, normalize(Light.Position - gBuffer.WorldPos), ContactShadowsLength, dither);
+    shadow.SurfaceShadow = min(shadow.SurfaceShadow, contactShadow);
 #endif
 
 	return GetShadowMask(shadow);