uniform float uTime;
uniform vec3 uLightDir;
uniform float uG;
uniform float uG2;
uniform float uExposure;
uniform sampler2D uStarfield;

varying vec2 vUV;
varying vec3 vRayleighColor;
varying vec3 vMieColor;
varying vec3 vDirection;
varying float vOpacity;
varying float vHeight;

void main(void)
{
    float cos = dot(uLightDir, vDirection) / length(vDirection);
    float cos2 = cos*cos;
    
    float rayleighPhase = 0.75 * (1.0 + 0.5*cos2);
    
    float miePhase = 1.5 * ((1.0 - uG2) / (2.0 + uG2)) * (1.0 + cos2) / pow(1.0 + uG2 - 2.0 * uG * cos, 1.5);
    
#ifdef LDR
    gl_FragColor = vec4((1.0 - exp(-uExposure * (rayleighPhase * vRayleighColor + miePhase * vMieColor))), vOpacity);
#else  // HDR
    gl_FragColor = vec4(rayleighPhase * vRayleighColor + miePhase * vMieColor, vOpacity);
#endif // LDR

    float nightmult = clamp(1.0 - max(gl_FragColor.x, max(gl_FragColor.y, gl_FragColor.z)) * 10.0, 0.0, 1.0);
    
//#ifdef STARFIELD
    gl_FragColor.xyz += nightmult * (vec3(0.05, 0.05, 0.1) * (2.0 - 0.75*clamp(-uLightDir.y, 0.0, 1.0)) * pow(vHeight,3.0) + texture2D(uStarfield, vUV + uTime).rgb * (0.35 + clamp(-uLightDir.y * 0.45, 0.0, 1.0)));
//#else  // NO STARFIELD
//    gl_FragColor.xyz += nightmult * (vec3(0.05, 0.05, 0.1) * (2.0 - 0.75*clamp(-uLightDir.y, 0.0, 1.0)) * pow(vHeight,3.0));
//#endif // STARFIELD
}