blackbody_approx.cpp

// https://portsmouth.github.io/Trinity/

// Approximate map from temperature in Kelvin to blackbody emission color.
// Valid from 1000 to 40000 K (and additionally 0 for pure full white)
vec3 colorTemperatureToRGB(const in float temperature)
{
  mat3 m = (temperature <= 6500.0) ? mat3(vec3(0.0, -2902.1955373783176, -8257.7997278925690),
	                                      vec3(0.0, 1669.5803561666639, 2575.2827530017594),
	                                      vec3(1.0, 1.3302673723350029, 1.8993753891711275)) :
	 								 mat3(vec3(1745.0425298314172, 1216.6168361476490, -8257.7997278925690),
   	                                      vec3(-2666.3474220535695, -2173.1012343082230, 2575.2827530017594),
	                                      vec3(0.55995389139931482, 0.70381203140554553, 1.8993753891711275));
  return mix(clamp(vec3(m[0] / (vec3(clamp(temperature, 1000.0, 40000.0)) + m[1]) + m[2]), vec3(0.0), vec3(1.0)),
             vec3(1.0),
             smoothstep(1000.0, 0.0, temperature));
}