#include <common>

uniform vec3 lightDirection;
uniform float g;

varying vec3 v3Direction;
varying vec3 c0;
varying vec3 c1;

// Calculates the Mie phase function
float getMiePhase(float fCos, float fCos2, float g, float g2){
  return 1.5 * ((1.0 - g2) / (2.0 + g2)) * (1.0 + fCos2) / pow(1.0 + g2 - 2.0 * g * fCos, 1.5);
}

// Calculates the Rayleigh phase function
float getRayleighPhase(float fCos2) {
  // return 0.75 + 0.75 * fCos2;
  return 0.75 * (2.0 + 0.5 * fCos2);
}

void main (void) {
  float fCos = dot(lightDirection, v3Direction) / length(v3Direction);
  float fCos2 = fCos * fCos;
  vec3 color =  getRayleighPhase(fCos2) * c0 +
          getMiePhase(fCos, fCos2, g, pow(g, 2.0)) * c1;
  gl_FragColor = vec4(color, 1.0);
  gl_FragColor.a = gl_FragColor.b;
}