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328 lines
14 KiB
HLSL
328 lines
14 KiB
HLSL
#ifndef SKY_COMMON_HLSLI
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#define SKY_COMMON_HLSLI
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#include "color_transform.hlsli"
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#include "math.hlsli"
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cbuffer SkyConstants : register(b13){
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float4 g_AerosolAbsorptionCrossSection;
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float4 g_AerosolScatteringCrossSection;
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float4 g_GroundAlbedo;
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float g_AerosolHeightScale;
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float g_AerosolTurbidity;
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float g_AerosolBaseDensity;
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float g_AerosolBackgroundDividedByBaseDensity;
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float g_OzoneMean;
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float g_FogDensity;
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float g_FogHeightOffset;
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float g_FogHeightScale;
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}
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// Configurable parameters
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// #define ANIMATE_SUN 1
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// // 0=equirectangular, 1=fisheye, 2=projection
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// #define CAMERA_TYPE 2
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// // 0=Background, 1=Desert Dust, 2=Maritime Clean, 3=Maritime Mineral,
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// // 4=Polar Antarctic, 5=Polar Artic, 6=Remote Continental, 7=Rural, 8=Urban
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//#define AEROSOL_TYPE 8
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// static const float SUN_ELEVATION_DEGREES = 0.0; // 0=horizon, 90=zenith
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// static const float EYE_ALTITUDE = 0.5; // km
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//static const int MONTH = 0; // 0-11, January to December
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//static const float AEROSOL_TURBIDITY = 1.0;
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//static const float4 GROUND_ALBEDO = 0.3;
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// // Ray marching steps. More steps mean better accuracy but worse performance
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// static const int TRANSMITTANCE_STEPS = 32;
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// static const int IN_SCATTERING_STEPS = 32;
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// // Camera settings
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static const float EXPOSURE = -4.0;
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// // For the "projection" type camera
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// static const float CAMERA_FOV = 90.0;
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// static const float CAMERA_YAW = 15.0;
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// static const float CAMERA_PITCH = -12.0;
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// static const float CAMERA_ROLL = 0.0;
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// // Debug
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// #define ENABLE_SPECTRAL 1
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// #define ENABLE_MULTIPLE_SCATTERING 1
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// #define ENABLE_AEROSOLS 1
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// #define SHOW_RELATIVE_LUMINANCE 0
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// #define TONEMAPPING_TECHNIQUE 0 // 0=ACES, 1=simple
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//-----------------------------------------------------------------------------
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// Constants
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// All parameters that depend on wavelength (float4) are sampled at
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// 630, 560, 490, 430 nanometers
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//static const float PI = 3.14159265358979323846;
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static const float INV_PI = 0.31830988618379067154;
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static const float INV_4PI = 0.25 * INV_PI;
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static const float PHASE_ISOTROPIC = INV_4PI;
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static const float RAYLEIGH_PHASE_SCALE = (3.0 / 16.0) * INV_PI;
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static const float g = 0.8;
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static const float gg = g*g;
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static const float EARTH_RADIUS = 6371.0e3; // km
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static const float ATMOSPHERE_THICKNESS = 100.0e3; // km
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static const float ATMOSPHERE_RADIUS = EARTH_RADIUS + ATMOSPHERE_THICKNESS;
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// static const float EYE_DISTANCE_TO_EARTH_CENTER = EARTH_RADIUS + EYE_ALTITUDE;
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// static const float SUN_ZENITH_COS_ANGLE = cos(radians(90.0 - SUN_ELEVATION_DEGREES));
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// static const float3 SUN_DIR = float3(-sqrt(1.0 - SUN_ZENITH_COS_ANGLE*SUN_ZENITH_COS_ANGLE), 0.0, SUN_ZENITH_COS_ANGLE);
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// Extraterrestial Solar Irradiance Spectra, units W * m^-2 * nm^-1
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// https://www.nrel.gov/grid/solar-resource/spectra.html
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static const float4 sun_spectral_irradiance = float4(1.679, 1.828, 1.986, 1.307);
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// Rayleigh scattering coefficient at sea level, units km^-1
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// "Rayleigh-scattering calculations for the terrestrial atmosphere"
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// by Anthony Bucholtz (1995).
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static const float4 molecular_scattering_coefficient_base = float4(6.605e-6, 1.067e-5, 1.842e-5, 3.156e-5);
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// Fog scattering/extinction cross section, units m^2 / molecules
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// Mie theory results for IOR of 1.333. Particle size is a log normal
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// distribution of mean diameter=15 and std deviation=0.4
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static const float4 fog_scattering_cross_section = float4(5.015e-10, 4.987e-10, 4.966e-10, 4.949e-10);
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// Ozone absorption cross section, units m^2 / molecules
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// "High spectral resolution ozone absorption cross-sections"
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// by V. Gorshelev et al. (2014).
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static const float4 ozone_absorption_cross_section = float4(3.472e-25, 3.914e-25, 1.349e-25, 11.03e-27);
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// Mean ozone concentration in Dobson for each month of the year.
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// static const float ozone_mean_monthly_dobson[] = {
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// 347.0, // January
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// 370.0, // February
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// 381.0, // March
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// 384.0, // April
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// 372.0, // May
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// 352.0, // June
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// 333.0, // July
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// 317.0, // August
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// 298.0, // September
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// 285.0, // October
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// 290.0, // November
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// 315.0 // December
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// };
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/*
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* Every aerosol type expects 5 parameters:
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* - Scattering cross section
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* - Absorption cross section
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* - Base density (km^-3)
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* - Background density (km^-3)
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* - Height scaling parameter
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* These parameters can be sent as uniforms.
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*
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* This model for aerosols and their corresponding parameters come from
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* "A Physically-Based Spatio-Temporal Sky Model"
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* by Guimera et al. (2018).
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*/
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// #if AEROSOL_TYPE == 0 // Background
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// static const float4 aerosol_absorption_cross_section = float4(4.5517e-19, 5.9269e-19, 6.9143e-19, 8.5228e-19);
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// static const float4 aerosol_scattering_cross_section = float4(1.8921e-26, 1.6951e-26, 1.7436e-26, 2.1158e-26);
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// static const float aerosol_base_density = 2.584e14;
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// static const float aerosol_background_density = 2e3;
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// #elif AEROSOL_TYPE == 1 // Desert Dust
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// static const float4 aerosol_absorption_cross_section = float4(4.6758e-16, 4.4654e-16, 4.1989e-16, 4.1493e-16);
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// static const float4 aerosol_scattering_cross_section = float4(2.9144e-16, 3.1463e-16, 3.3902e-16, 3.4298e-16);
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// static const float aerosol_base_density = 1.8662e15;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 2.0;
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// #elif AEROSOL_TYPE == 2 // Maritime Clean
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// static const float4 aerosol_absorption_cross_section = float4(6.3312e-19, 7.5567e-19, 9.2627e-19, 1.0391e-18);
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// static const float4 aerosol_scattering_cross_section = float4(4.6539e-26, 2.721e-26, 4.1104e-26, 5.6249e-26);
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// static const float aerosol_base_density = 2.0266e14;
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// static const float aerosol_background_density = 2e6;
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// static const float aerosol_height_scale = 0.9;
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// #elif AEROSOL_TYPE == 3 // Maritime Mineral
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// static const float4 aerosol_absorption_cross_section = float4(6.9365e-19, 7.5951e-19, 8.2423e-19, 8.9101e-19);
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// static const float4 aerosol_scattering_cross_section = float4(2.3699e-19, 2.2439e-19, 2.2126e-19, 2.021e-19);
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// static const float aerosol_base_density = 2.0266e14;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 2.0;
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// #elif AEROSOL_TYPE == 4 // Polar Antarctic
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// static const float4 aerosol_absorption_cross_section = float4(1.3399e-16, 1.3178e-16, 1.2909e-16, 1.3006e-16);
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// static const float4 aerosol_scattering_cross_section = float4(1.5506e-19, 1.809e-19, 2.3069e-19, 2.5804e-19);
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// static const float aerosol_base_density = 2.3864e13;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 30.0;
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// #elif AEROSOL_TYPE == 5 // Polar Arctic
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// static const float4 aerosol_absorption_cross_section = float4(1.0364e-16, 1.0609e-16, 1.0193e-16, 1.0092e-16);
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// static const float4 aerosol_scattering_cross_section = float4(2.1609e-17, 2.2759e-17, 2.5089e-17, 2.6323e-17);
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// static const float aerosol_base_density = 2.3864e13;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 30.0;
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// #elif AEROSOL_TYPE == 6 // Remote Continental
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// static const float4 aerosol_absorption_cross_section = float4(4.5307e-18, 5.0662e-18, 4.4877e-18, 3.7917e-18);
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// static const float4 aerosol_scattering_cross_section = float4(1.8764e-18, 1.746e-18, 1.6902e-18, 1.479e-18);
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// static const float aerosol_base_density = 6.103e15;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 0.73;
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// #elif AEROSOL_TYPE == 7 // Rural
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// static const float4 aerosol_absorption_cross_section = float4(5.0393e-23, 8.0765e-23, 1.3823e-22, 2.3383e-22);
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// static const float4 aerosol_scattering_cross_section = float4(2.6004e-22, 2.4844e-22, 2.8362e-22, 2.7494e-22);
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// static const float aerosol_base_density = 8.544e15;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 0.73;
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// #elif AEROSOL_TYPE == 8 // Urban
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// static const float4 aerosol_absorption_cross_section = float4(2.8722e-24, 4.6168e-24, 7.9706e-24, 1.3578e-23);
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// static const float4 aerosol_scattering_cross_section = float4(1.5908e-22, 1.7711e-22, 2.0942e-22, 2.4033e-22);
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// static const float aerosol_base_density = 1.3681e17;
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// static const float aerosol_background_density = 2e3;
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// static const float aerosol_height_scale = 0.73;
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// #endif
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//static const float aerosol_background_divided_by_base_density = aerosol_background_density / aerosol_base_density;
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// static const float fog_density = 29811535.0;
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// static const float fog_scale_height = .01;
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// static const float fog_height_offset = 0.325;
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//-----------------------------------------------------------------------------
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/*
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* Helper function to obtain the transmittance to the top of the atmosphere
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* from Buffer A.
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*/
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float4 transmittance_from_lut(Texture2D lut, SamplerState lut_sampler, float cos_theta, float normalized_altitude)
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{
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float u = saturate(cos_theta * 0.5 + 0.5);
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float v = saturate(normalized_altitude);
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return lut.SampleLevel(lut_sampler, float2(u, v), 0.);
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}
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/*
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* Returns the distance between ro and the first intersection with the sphere
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* or -1.0 if there is no intersection. The sphere's origin is (0,0,0).
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* -1.0 is also returned if the ray is pointing away from the sphere.
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*/
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float ray_sphere_intersection(float3 ro, float3 rd, float radius)
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{
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float b = dot(ro, rd);
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float c = dot(ro, ro) - radius*radius;
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if (c > 0.0 && b > 0.0) return -1.0;
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float d = b*b - c;
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if (d < 0.0) return -1.0;
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if (d > b*b) return (-b+sqrt(d));
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return (-b-sqrt(d));
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}
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/*
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* Rayleigh phase function.
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*/
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float molecular_phase_function(float cos_theta)
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{
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return RAYLEIGH_PHASE_SCALE * (1.0 + cos_theta*cos_theta);
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}
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/*
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* Henyey-Greenstrein phase function.
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*/
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float aerosol_phase_function(float cos_theta)
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{
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float den = 1.0 + gg + 2.0 * g * cos_theta;
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return INV_4PI * (1.0 - gg) / (den * sqrt(den));
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}
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float4 get_multiple_scattering(Texture2D transmittance_lut, SamplerState lut_sampler, float cos_theta, float normalized_height, float d)
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{
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// Solid angle subtended by the planet from a point at d distance
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// from the planet center.
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float omega = 2.0 * PI * (1.0 - sqrt(max(0., d*d - EARTH_RADIUS*EARTH_RADIUS)) / d);
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float4 T_to_ground = transmittance_from_lut(transmittance_lut, lut_sampler, cos_theta, 0.0);
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float4 T_ground_to_sample =
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transmittance_from_lut(transmittance_lut, lut_sampler, 1.0, 0.0) /
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transmittance_from_lut(transmittance_lut, lut_sampler, 1.0, normalized_height);
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// 2nd order scattering from the ground
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float4 L_ground = PHASE_ISOTROPIC * omega * (g_GroundAlbedo / PI) * T_to_ground * T_ground_to_sample * cos_theta;
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// Fit of Earth's multiple scattering coming from other points in the atmosphere
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float4 L_ms = 0.02 * float4(0.217, 0.347, 0.594, 1.0) * (1.0 / (1.0 + 5.0 * exp(-17.92 * cos_theta)));
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return L_ms + L_ground;
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}
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/*
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* Return the molecular volume scattering coefficient (km^-1) for a given altitude
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* in kilometers.
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*/
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float4 get_molecular_scattering_coefficient(float h)
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{
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return molecular_scattering_coefficient_base * exp(-0.07771971 * pow(h, 1.16364243));
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}
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/*
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* Return the molecular volume absorption coefficient (km^-1) for a given altitude
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* in kilometers.
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*/
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float4 get_molecular_absorption_coefficient(float h)
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{
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h += 1e-4; // Avoid division by 0
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float t = log(h) - 3.22261;
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float density = 3.78547397e17 * (1.0 / h) * exp(-t * t * 5.55555555);
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return ozone_absorption_cross_section * g_OzoneMean * density;
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}
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/*
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* Return the fog volume scattering coefficient (m^-1) for a given altitude in
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* kilometers.
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*
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* Fog (or mist, depending on density) is a special kind of aerosol consisting
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* of water droplets or ice crystals. Visibility is mostly dependent on fog.
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*/
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float4 get_fog_scattering_coefficient(float h)
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{
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if (g_FogDensity > 0.0) {
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return fog_scattering_cross_section * g_FogDensity
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* min(1.0, exp((-h + g_FogHeightOffset) / g_FogHeightScale));
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} else {
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return 0.0;
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}
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}
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float get_aerosol_density(float h)
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{
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return g_AerosolBaseDensity * (exp(-h / g_AerosolHeightScale)
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+ g_AerosolBackgroundDividedByBaseDensity);
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}
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/*
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* Get the collision coefficients (scattering and absorption) of the
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* atmospheric medium for a given point at an altitude h.
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*/
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void get_atmosphere_collision_coefficients(in float h,
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out float4 aerosol_absorption,
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out float4 aerosol_scattering,
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out float4 molecular_absorption,
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out float4 molecular_scattering,
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out float4 fog_scattering,
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out float4 extinction)
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{
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h = max(h, 1.e-3); // In case height is negative
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h *= 1.e-3;
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float aerosol_density = get_aerosol_density(h);
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aerosol_absorption = g_AerosolAbsorptionCrossSection * aerosol_density * g_AerosolTurbidity;
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aerosol_scattering = g_AerosolScatteringCrossSection * aerosol_density * g_AerosolTurbidity;
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molecular_absorption = get_molecular_absorption_coefficient(h);
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molecular_scattering = get_molecular_scattering_coefficient(h);
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fog_scattering = get_fog_scattering_coefficient(h);
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extinction = aerosol_absorption + aerosol_scattering + molecular_absorption + molecular_scattering + fog_scattering;
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}
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//-----------------------------------------------------------------------------
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// Spectral rendering stuff
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static const float4x3 M = float4x3(
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137.672389239975, -8.632904716299537, -1.7181567391931372,
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32.549094028629234, 91.29801417199785, -12.005406444382531,
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-38.91428392614275, 34.31665471469816, 29.89044807197628,
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8.572844237945445, -11.103384660054624, 117.47585277566478
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);
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float3 linear_srgb_from_spectral_samples(float4 L)
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{
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return REC709_to_XYZ(mul(L, M));
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}
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#endif |