uniform mat4 inverseViewMatrix;
uniform mat4 inverseProjectionMatrix;
uniform vec3 cameraPosition;
uniform vec3 ellipsoidCenter;
uniform mat4 inverseEllipsoidMatrix;
uniform vec3 altitudeCorrection;
uniform vec3 ellipsoidRadii;
uniform float idealSphereAlpha;

varying vec3 vCameraPosition;
varying vec3 vRayDirection;
varying vec3 vEllipsoidCenter;
varying vec3 vGeometryEllipsoidCenter;
varying vec3 vEllipsoidRadiiSquared;

void getCameraRay(out vec3 origin, out vec3 direction) {
  bool isPerspective = inverseProjectionMatrix[2][3] != 0.0; // 4th entry in the 3rd column

  if (isPerspective) {
    // Calculate the camera ray for a perspective camera.
    vec4 viewPosition = inverseProjectionMatrix * vec4(position, 1.0);
    vec4 worldDirection = inverseViewMatrix * vec4(viewPosition.xyz, 0.0);
    origin = cameraPosition;
    direction = worldDirection.xyz;
  } else {
    // Unprojected points to calculate direction.
    vec4 nearPoint = inverseProjectionMatrix * vec4(position.xy, -1.0, 1.0);
    vec4 farPoint = inverseProjectionMatrix * vec4(position.xy, -0.9, 1.0);
    nearPoint /= nearPoint.w;
    farPoint /= farPoint.w;

    // Calculate world values.
    vec4 worldDirection = inverseViewMatrix * vec4(farPoint.xyz - nearPoint.xyz, 0.0);
    vec4 worldOrigin = inverseViewMatrix * nearPoint;

    // Outputs
    direction = worldDirection.xyz;
    origin = worldOrigin.xyz;
  }
}

void mainSupport() {
  vec3 direction, origin;
  getCameraRay(origin, direction);

  mat3 rotation = mat3(inverseEllipsoidMatrix);
  vCameraPosition = rotation * origin.xyz * METER_TO_LENGTH_UNIT;
  vRayDirection = rotation * direction.xyz;

  vEllipsoidCenter = (ellipsoidCenter + altitudeCorrection) * METER_TO_LENGTH_UNIT;
  #ifdef CORRECT_GEOMETRIC_ERROR
  // Gradually turn off altitude correction for aerial perspective as geometric
  // error correction takes effect.
  // See: https://github.com/takram-design-engineering/three-geospatial/pull/23#issuecomment-2542914656
  vGeometryEllipsoidCenter =
    (ellipsoidCenter + mix(altitudeCorrection, vec3(0.0), idealSphereAlpha)) * METER_TO_LENGTH_UNIT;
  #else
  vGeometryEllipsoidCenter = vEllipsoidCenter;
  #endif // CORRECT_GEOMETRIC_ERROR

  vec3 radii = ellipsoidRadii * METER_TO_LENGTH_UNIT;
  vEllipsoidRadiiSquared = radii * radii;
}