// Based on: https://github.com/ebruneton/precomputed_atmospheric_scattering/blob/master/atmosphere/definitions.glsl

/**
 * Copyright (c) 2017 Eric Bruneton
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

#define assert(x)

#define Length float
#define Wavelength float
#define Angle float
#define SolidAngle float
#define Power float
#define LuminousPower float

#define Number float
#define InverseLength float
#define Area float
#define Volume float
#define NumberDensity float
#define Irradiance float
#define Radiance float
#define SpectralPower float
#define SpectralIrradiance float
#define SpectralRadiance float
#define SpectralRadianceDensity float
#define ScatteringCoefficient float
#define InverseSolidAngle float
#define LuminousIntensity float
#define Luminance float
#define Illuminance float

// A generic function from Wavelength to some other type.
#define AbstractSpectrum vec3
// A function from Wavelength to Number.
#define DimensionlessSpectrum vec3
// A function from Wavelength to SpectralPower.
#define PowerSpectrum vec3
// A function from Wavelength to SpectralIrradiance.
#define IrradianceSpectrum vec3
// A function from Wavelength to SpectralRadiance.
#define RadianceSpectrum vec3
// A function from Wavelength to SpectralRadianceDensity.
#define RadianceDensitySpectrum vec3
// A function from Wavelength to ScatteringCoefficient.
#define ScatteringSpectrum vec3

// A position in 3D (3 length values).
#define Position vec3
// A unit direction vector in 3D (3 unit-less values).
#define Direction vec3
// A vector of 3 luminance values.
#define Luminance3 vec3
// A vector of 3 illuminance values.
#define Illuminance3 vec3

#define TransmittanceTexture sampler2D
#define AbstractScatteringTexture sampler3D
#define ReducedScatteringTexture sampler3D
#define ScatteringTexture sampler3D
#define ScatteringDensityTexture sampler3D
#define IrradianceTexture sampler2D

const Length m = 1.0;
const Wavelength nm = 1.0;
const Angle rad = 1.0;
const SolidAngle sr = 1.0;
const Power watt = 1.0;
const LuminousPower lm = 1.0;

#if !defined(PI)
const float PI = 3.14159265358979323846;
#endif // !defined(PI)

const Length km = 1000.0 * m;
const Area m2 = m * m;
const Volume m3 = m * m * m;
const Angle pi = PI * rad;
const Angle deg = pi / 180.0;
const Irradiance watt_per_square_meter = watt / m2;
const Radiance watt_per_square_meter_per_sr = watt / (m2 * sr);
const SpectralIrradiance watt_per_square_meter_per_nm = watt / (m2 * nm);
const SpectralRadiance watt_per_square_meter_per_sr_per_nm = watt / (m2 * sr * nm);
const SpectralRadianceDensity watt_per_cubic_meter_per_sr_per_nm = watt / (m3 * sr * nm);
const LuminousIntensity cd = lm / sr;
const LuminousIntensity kcd = 1000.0 * cd;
const Luminance cd_per_square_meter = cd / m2;
const Luminance kcd_per_square_meter = kcd / m2;

struct DensityProfileLayer {
  Length width;
  Number exp_term;
  InverseLength exp_scale;
  InverseLength linear_term;
  Number constant_term;
};

struct DensityProfile {
  DensityProfileLayer layers[2];
};

// See AtmosphereParameter.ts for further details.
struct AtmosphereParameters {
  IrradianceSpectrum solar_irradiance;
  Angle sun_angular_radius;
  Length bottom_radius;
  Length top_radius;
  DensityProfile rayleigh_density;
  ScatteringSpectrum rayleigh_scattering;
  DensityProfile mie_density;
  ScatteringSpectrum mie_scattering;
  ScatteringSpectrum mie_extinction;
  Number mie_phase_function_g;
  DensityProfile absorption_density;
  ScatteringSpectrum absorption_extinction;
  DimensionlessSpectrum ground_albedo;
  Number mu_s_min;
};