use czm_tanh()

packages/engine/Source/Shaders/AtmosphereCommon.glsl

@@ -11,14 +11,6 @@ const float ATMOSPHERE_THICKNESS = 111e3; // The thickness of the atmosphere in
 const int PRIMARY_STEPS_MAX = 16; // Maximum number of times the ray from the camera to the world position (primary ray) is sampled.
 const int LIGHT_STEPS_MAX = 4; // Maximum number of times the light is sampled from the light source's intersection with the atmosphere to a sample position on the primary ray.
 
-/**
- * Rational approximation to tanh(x)
-*/
-float approximateTanh(float x) {
-    float x2 = x * x;
-    return max(-1.0, min(+1.0, x * (27.0 + x2) / (27.0 + 9.0 * x2)));
-}
-
 /**
  * This function computes the colors contributed by Rayliegh and Mie scattering on a given ray, as well as
  * the transmittance value for the ray.
@@ -65,7 +57,7 @@ void computeScattering(
     float x = 1e-7 * primaryRayAtmosphereIntersect.stop / length(primaryRayLength);
     // Value close to 0.0: close to the horizon
     // Value close to 1.0: above in the sky
-    float w_stop_gt_lprl = 0.5 * (1.0 + approximateTanh(x));
+    float w_stop_gt_lprl = 0.5 * (1.0 + czm_approximateTanh(x));
 
     // The ray should start from the first intersection with the outer atmopshere, or from the camera position, if it is inside the atmosphere.
     float start_0 = primaryRayAtmosphereIntersect.start;
@@ -77,7 +69,7 @@ void computeScattering(
     // (1) from outer space we have to use more ray steps to get a realistic rendering
     // (2) within atmosphere we need fewer steps for faster rendering
     float x_o_a = start_0 - ATMOSPHERE_THICKNESS; // ATMOSPHERE_THICKNESS used as an ad-hoc constant, no precise meaning here, only the order of magnitude matters
-    float w_inside_atmosphere = 1.0 - 0.5 * (1.0 + approximateTanh(x_o_a));
+    float w_inside_atmosphere = 1.0 - 0.5 * (1.0 + czm_approximateTanh(x_o_a));
     int PRIMARY_STEPS = PRIMARY_STEPS_MAX - int(w_inside_atmosphere * 12.0); // Number of times the ray from the camera to the world position (primary ray) is sampled.
     int LIGHT_STEPS = LIGHT_STEPS_MAX - int(w_inside_atmosphere * 2.0); // Number of times the light is sampled from the light source's intersection with the atmosphere to a sample position on the primary ray.