SSAO: Fix FastACos approximation

MikhailGorobets · MikhailGorobets · commit 427fc3375104 · 2026-04-29T18:58:49.000+06:00
diff --git a/Shaders/PostProcess/ScreenSpaceAmbientOcclusion/private/SSAO_ComputeAmbientOcclusion.fx b/Shaders/PostProcess/ScreenSpaceAmbientOcclusion/private/SSAO_ComputeAmbientOcclusion.fx
@@ -46,8 +46,9 @@ float2 ComputeSliceDirection(float Xi, int Index)
 
 float FastACos(float Value)
 {
-    float Result = -0.156583 * Value + M_HALF_PI;
-    Result *= sqrt(1.0 - abs(Value));
+    float AbsValue = abs(Value);
+    float Result = -0.156583 * AbsValue + M_HALF_PI;
+    Result *= sqrt(1.0 - AbsValue);
     return (Value >= 0.0) ? Result : M_PI - Result;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -46,8 +46,9 @@ float2 ComputeSliceDirection(float Xi, int Index)`
`46`	`46`
`47`	`47`	`float FastACos(float Value)`
`48`	`48`	`{`
`49`		`- float Result = -0.156583 * Value + M_HALF_PI;`
`50`		`- Result *= sqrt(1.0 - abs(Value));`
	`49`	`+ float AbsValue = abs(Value);`
	`50`	`+ float Result = -0.156583 * AbsValue + M_HALF_PI;`
	`51`	`+ Result *= sqrt(1.0 - AbsValue);`
`51`	`52`	`return (Value >= 0.0) ? Result : M_PI - Result;`
`52`	`53`	`}`
`53`	`54`