SSAO: added SSAO_MAX_HISTORY_LENGTH macro

Author: TheMostDiligent

Shaders/PostProcess/ScreenSpaceAmbientOcclusion/private/SSAO_ComputeTemporalAccumulation.fx

@@ -140,7 +140,7 @@ ProjectionDesc ComputeReprojection(float2 PrevPos, float CurrDepth)
             LoadHistory(FetchCoords.xw),
             LoadHistory(FetchCoords.zw)
         );
-        History = min(float4(16.0, 16.0, 16.0, 16.0), History + float4(1.0, 1.0, 1.0, 1.0));
+        History = min(History + float4(1.0, 1.0, 1.0, 1.0), float4(SSAO_MAX_HISTORY_LENGTH, SSAO_MAX_HISTORY_LENGTH, SSAO_MAX_HISTORY_LENGTH, SSAO_MAX_HISTORY_LENGTH));
         Desc.Occlusion = dot(PrevOcclusion, Weights) / TotalWeight;
         Desc.History = dot(History, Weights) / TotalWeight;
     }

Shaders/PostProcess/ScreenSpaceAmbientOcclusion/public/ScreenSpaceAmbientOcclusionStructures.fxh

@@ -49,6 +49,10 @@
 // Determines the similarity of the depth in the current and previous frame to calculate the disoclusion in the temporal accumulation step
 #define SSAO_DISOCCLUSION_DEPTH_THRESHOLD 0.01
 
+// Maximum history length in the temporal accumulation step.
+// Higher values reduce noise for the price of increased ghosting.
+#define SSAO_MAX_HISTORY_LENGTH 16.0
+
 struct ScreenSpaceAmbientOcclusionAttribs
 {
     // The value defines world space radius of ambient occlusion