Color temperature to linearized sRGB color

temp.cpp

  // Recalculate the color.
  PN_stdfloat mm = 1000.0 / temperature;
  PN_stdfloat mm2 = mm * mm;
  PN_stdfloat mm3 = mm2 * mm;
  PN_stdfloat x, y;

  if (temperature < 4000) {
    x = -0.2661239 * mm3 - 0.2343580 * mm2 + 0.8776956 * mm + 0.179910;
  } else {
    x = -3.0258469 * mm3 + 2.1070379 * mm2 + 0.2226347 * mm + 0.240390;
  }

  PN_stdfloat x2 = x * x;
  PN_stdfloat x3 = x2 * x;
  if (temperature < 2222) {
    y = -1.1063814 * x3 - 1.34811020 * x2 + 2.18555832 * x - 0.20219683;
  } else if (temperature < 4000) {
    y = -0.9549476 * x3 - 1.37418593 * x2 + 2.09137015 * x - 0.16748867;
  } else {
    y =  3.0817580 * x3 - 5.87338670 * x2 + 3.75112997 * x - 0.37001483;
  }

  // xyY to XYZ, assuming Y=1.
  LVecBase3 xyz(x / y, 1, (1 - x - y) / y);

  // Convert XYZ to linearized sRGB.
  const static LMatrix3 xyz_to_rgb(
    3.2406255, -0.9689307, 0.0557101,
    -1.537208, 1.8757561, -0.2040211,
    -0.4986286, 0.0415175, 1.0569959);

  LColor color(xyz_to_rgb.xform(xyz), 1);