precision mediump float;

uniform vec3 v3LightPosition;
uniform float g;
uniform float g2;
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;
}

void main (void) {
	float fCos = dot(v3LightPosition, v3Direction) / length(v3Direction);
	float fCos2 = fCos * fCos;
	vec3 color =	getRayleighPhase(fCos2) * c0 +
					getMiePhase(fCos, fCos2, g, g2) * c1;
 	gl_FragColor = vec4(color, 1.0);
	gl_FragColor.a = gl_FragColor.b;
}