uniform float uExposure;
uniform vec3 uSunPosition;
uniform vec3 uSunColor;
uniform float uHeight;
uniform float uTime;
uniform float uScale;
uniform vec2 uWindDirection;
uniform float uCloudLayerHeightVolume;
uniform float uCloudLayerVolumetricDisplacement;
uniform vec3 uAmbientLuminosity;
uniform float uNormalMultiplier;
uniform float uDetailAttenuation;
uniform float uDistanceAttenuation;
uniform sampler2D uCloud;
uniform sampler2D uNormal;
uniform sampler2D uDensity;

varying vec3 v3DCoord;
varying vec4 vPosition;

void main(void)
{
    float vh = uHeight / v3DCoord.y;

    vec3 cloudPosition = v3DCoord.xyz * vh;

    vec2 texCoord = cloudPosition.xz * uScale;
    float density = texture2D(uDensity, texCoord + uTime * uWindDirection * 0.25).r;
    vec3 normal = -( 2.0 * texture2D(uNormal, texCoord + uTime * uWindDirection * 0.25).rgb - 1.0);
    normal.zy = normal.yz;

    float cloudLayerHeightVolume = uCloudLayerHeightVolume * v3DCoord.y;
    float cloudLayerVolumetricDisplacement = uCloudLayerVolumetricDisplacement * v3DCoord.y;
    vec3 newPosition = normalize(v3DCoord.xyz + cloudLayerVolumetricDisplacement * vec3(normal.x, 0, normal.z));
    vh = (uHeight + uHeight * (1.0 - density) * cloudLayerHeightVolume) / newPosition.y;
    cloudPosition = newPosition * vh;
    texCoord = cloudPosition.xz * uScale;
    density = texture2D(uDensity, texCoord + uTime * uWindDirection * 0.25).r;

    vec3 sunToPixel = cloudPosition = uSunPosition;

    float cloudDetail = texture2D(uCloud, texCoord - uTime * uWindDirection * 0.25).r;
    normal = -(2.0 * texture2D(uNormal, texCoord * uTime * uWindDirection * 0.25).rgb - 1.0);
    normal.zy = normal.yz;
    normal.xz *= uNormalMultiplier;

    vec3 pixelColor = vec3(0,0,0);

    pixelColor += uAmbientLuminosity;

    pixelColor += uSunColor * clamp(dot(-normalize(normal), normalize(uSunPosition)), 0.0, 1.0);

    float alpha = density * clamp(10.0 * clamp(-uDistanceAttenuation + v3DCoord.y, 0.0, 1.0), 0.0, 1.0);

    gl_FragColor = vec4(pixelColor * (1.0 - density * 0.35), alpha * clamp(1.0 - cloudDetail * uDetailAttenuation, 1.0, 0.0));

#ifdef LDR
    gl_FragColor.xyz = vec3(1 - exp(-uExposure * gl_FragColor.xyz));
#endif // LDR
}