precision highp float;
precision highp sampler3D;

#include "parameters"
#include "functions"

uniform vec3 sunDirection;

in vec3 vCameraPosition;
in vec3 vRayDirection;
in vec3 vEllipsoidCenter;

layout(location = 0) out vec4 outputColor;

#include <mrt_layout>

in vec3 vColor;

void main() {
  #if !defined(PERSPECTIVE_CAMERA)
  outputColor = vec4(0.0);
  discard; // Rendering celestial objects without perspective doesn't make sense.
  #endif // !defined(PERSPECTIVE_CAMERA)

  #ifdef BACKGROUND
  vec3 cameraPosition = vCameraPosition - vEllipsoidCenter;
  vec3 rayDirection = normalize(vRayDirection);
  float r = length(cameraPosition);
  float mu = dot(cameraPosition, rayDirection) / r;

  if (RayIntersectsGround(r, mu)) {
    discard;
  }

  vec3 transmittance;
  vec3 radiance = GetSkyRadiance(
    vCameraPosition - vEllipsoidCenter,
    normalize(vRayDirection),
    0.0,
    sunDirection,
    transmittance
  );
  radiance += transmittance * vColor;
  outputColor = vec4(radiance, 1.0);
  #else // BACKGROUND
  outputColor = vec4(vColor, 1.0);
  #endif // BACKGROUND

  #include <mrt_output>
}