Use slang's stdlib fn

Author: SaschaWillems

shaders/slang/hdr/gbuffer.slang

@@ -105,7 +105,7 @@ FSOutput fragmentMain(VSOutput input)
 				fresnel *= (1.0 - F0);
 				fresnel += F0;
 
-				float spec = (fresnel * geoAtt) / (NdotV * NdotL * 3.14);
+				float spec = (fresnel * geoAtt) / (NdotV * NdotL * float.getPi());
 
                 color = samplerEnvMap.Sample(reflect(-wViewVec, wNormal));