precision highp float;
precision highp sampler3D;

#define RECIPROCAL_PI (0.3183098861837907)

#include "core/raySphereIntersection"
#include "parameters"
#include "functions"
#include "sky"

uniform vec3 sunDirection;
uniform vec3 moonDirection;
uniform float moonAngularRadius;
uniform float lunarRadianceScale;
uniform vec3 groundAlbedo;

#ifdef HAS_SHADOW_LENGTH
uniform sampler2D shadowLengthBuffer;
#endif // HAS_SHADOW_LENGTH

in vec2 vUv;
in vec3 vCameraPosition;
in vec3 vRayDirection;
in vec3 vEllipsoidCenter;

layout(location = 0) out vec4 outputColor;

#include <mrt_layout>

bool rayIntersectsGround(const vec3 cameraPosition, const vec3 rayDirection) {
  float r = length(cameraPosition);
  float mu = dot(cameraPosition, rayDirection) / r;
  return mu < 0.0 && r * r * (mu * mu - 1.0) + u_bottom_radius * u_bottom_radius >= 0.0;
}

void main() {
  float shadowLength = 0.0;
  #ifdef HAS_SHADOW_LENGTH
  shadowLength = texture(shadowLengthBuffer, vUv).r;
  #endif // HAS_SHADOW_LENGTH

  vec3 cameraPosition = vCameraPosition - vEllipsoidCenter;
  vec3 rayDirection = normalize(vRayDirection);

  #ifdef GROUND_ALBEDO

  bool intersectsGround = rayIntersectsGround(cameraPosition, rayDirection);
  if (intersectsGround) {
    float distanceToGround = raySphereFirstIntersection(
      cameraPosition,
      rayDirection,
      u_bottom_radius
    );
    vec3 groundPosition = rayDirection * distanceToGround + cameraPosition;
    vec3 surfaceNormal = normalize(groundPosition);
    vec3 skyIrradiance;
    vec3 sunIrradiance = GetSunAndSkyIrradiance(
      cameraPosition,
      surfaceNormal,
      sunDirection,
      skyIrradiance
    );
    vec3 transmittance;
    vec3 inscatter = GetSkyRadianceToPoint(
      cameraPosition,
      u_bottom_radius * surfaceNormal,
      shadowLength,
      sunDirection,
      transmittance
    );
    vec3 radiance = groundAlbedo * RECIPROCAL_PI * (sunIrradiance + skyIrradiance);
    outputColor.rgb = radiance * transmittance + inscatter;
  } else {
    outputColor.rgb = getSkyRadiance(
      cameraPosition,
      rayDirection,
      shadowLength,
      sunDirection,
      moonDirection,
      moonAngularRadius,
      lunarRadianceScale
    );
  }

  #else // GROUND_ALBEDO

  outputColor.rgb = getSkyRadiance(
    cameraPosition,
    rayDirection,
    shadowLength,
    sunDirection,
    moonDirection,
    moonAngularRadius,
    lunarRadianceScale
  );

  #endif // GROUND_ALBEDO

  outputColor.a = 1.0;

  #include <mrt_output>
}