ReflectanceToIOR.osl

/* 
Reflectance to IOR by Saul Espinosa for Redshift 3D
OSL node to allow for the older rsMaterial Reflectivity style Input 
for the RS Standard Surface. Outputs a Specular Reflection Color and IOR output.

Last Modified : 5/16/2022

*/
shader ReflectanceToIOR
[[ string help     = "Convert Reflectivity Value to Reflection Color and IOR",
   string label    = "Reflectance To IOR"
]]
(
	color Reflectivity = 0.04 
		[[	string page = "Input", 
			float min = 0, 
			float max = 1
		]],
	
	output color ReflectionColor = 0.0,
	output float IOR = 0.0,
)
{

// Reflection Color = RGB to Hue Saturation and 1.0 Value
	color convert = transformc ("hsv", Reflectivity );
	float r = convert[0], g = convert[1], b = convert[2];
	color conversion = transformc ("hsv", "rgb", vector(r,g,1.0));
	ReflectionColor = conversion;

// IOR=(SQRT(Reflectance Value)+1)/(1-SQRT(Reflectance Value))

	IOR = (sqrt(b)+1) / (1-sqrt(b));
}