Annotate Rayleigh-related functions in SystemBody

src/galaxy/SystemBody.cpp

@@ -262,6 +262,10 @@ bool SystemBody::IsScoopable() const
 	return false;
 }
 
+// this is a reduced version of original Rayleigh scattering function used to compute density once per planet
+// (at least it meant not to be once per frame) given:
+// planet radius, height of atmosphere (not its radius), length of perpendicular between ray and planet center, lapse rate at which density fades out by rate of e
+// this function is used in GetCoefficients
 // all input units are in km
 double SystemBody::ComputeDensity(const double radius, const double atmosphereHeight, const double h, const double baricStep) const
 {
@@ -283,13 +287,20 @@ double SystemBody::ComputeDensity(const double radius, const double atmosphereHe
         return density;
 }
 
+// these coefficients are to be passed into shaders, meant to accelerate scattering computation per-pixel
+// instead of sampling each one (which I suspect is VERY SLOW)
 // all input units are in km
 vector3f SystemBody::GetCoefficients(const double radius, const double atmHeight, const double baricStep) const
 {
 	float k, b, c;
+
+	// compute full out-scattering densities at 0 and 1 km heights
+	// k = density at 0 km
+	// b = log(density0km / density1km) - log is used to multiply it by actual height
 	k = ComputeDensity(radius, atmHeight, 0.f, baricStep);
 	b = log(k / ComputeDensity(radius, atmHeight, 1.f, baricStep));
 
+	// compute c - erf coefficient, which adjusts slope of erf near t=0 to match actual in-scattering
 	float erf1_minus_erf0 = 0.421463;
 	float sHeight = sqrt(radius*radius + 1.f) - radius;
 	float c1 = exp(-sHeight / baricStep);