💿🐜 Antkeeper source code
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301 lines
11 KiB
301 lines
11 KiB
/*
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* Copyright (C) 2021 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "entity/systems/astronomy.hpp"
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#include "astro/apparent-size.hpp"
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#include "entity/components/blackbody.hpp"
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#include "entity/components/transform.hpp"
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#include "geom/intersection.hpp"
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#include "color/color.hpp"
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#include "physics/orbit/orbit.hpp"
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#include "physics/time/ut1.hpp"
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#include "physics/light/photometry.hpp"
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#include "physics/light/luminosity.hpp"
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#include "physics/light/refraction.hpp"
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#include "physics/atmosphere.hpp"
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#include "geom/cartesian.hpp"
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#include <iostream>
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namespace entity {
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namespace system {
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template <class T>
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math::vector3<T> transmittance(T depth_r, T depth_m, T depth_o, const math::vector3<T>& beta_r, const math::vector3<T>& beta_m)
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{
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math::vector3<T> transmittance_r = beta_r * depth_r;
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math::vector3<T> transmittance_m = beta_m * 1.1 * depth_m;
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math::vector3<T> transmittance_o = {0, 0, 0};
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math::vector3<T> t = transmittance_r + transmittance_m + transmittance_o;
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t.x = std::exp(-t.x);
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t.y = std::exp(-t.y);
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t.z = std::exp(-t.z);
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return t;
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}
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astronomy::astronomy(entity::registry& registry):
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updatable(registry),
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universal_time(0.0),
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time_scale(1.0),
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reference_entity(entt::null),
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observer_location{0, 0, 0},
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sun_light(nullptr),
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sky_pass(nullptr)
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{
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// Construct reference frame which transforms coordinates from SEZ to EZS
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sez_to_ezs = physics::frame<double>
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{
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{0, 0, 0},
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math::normalize
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(
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math::quaternion<double>::rotate_x(-math::half_pi<double>) *
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math::quaternion<double>::rotate_z(-math::half_pi<double>)
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)
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};
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// Construct reference frame which transforms coordinates from EZS to SEZ
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ezs_to_sez = sez_to_ezs.inverse();
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registry.on_construct<entity::component::celestial_body>().connect<&astronomy::on_celestial_body_construct>(this);
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registry.on_replace<entity::component::celestial_body>().connect<&astronomy::on_celestial_body_replace>(this);
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}
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void astronomy::update(double t, double dt)
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{
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// Add scaled timestep to current time
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set_universal_time(universal_time + dt * time_scale);
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// Abort if no reference body
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if (reference_entity == entt::null)
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return;
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// Abort if either reference body or orbit have not been set
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if (!registry.has<entity::component::orbit>(reference_entity) || !registry.has<entity::component::celestial_body>(reference_entity))
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return;
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const entity::component::orbit& reference_orbit = registry.get<entity::component::orbit>(reference_entity);
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const entity::component::celestial_body& reference_body = registry.get<entity::component::celestial_body>(reference_entity);
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// Determine axial rotation at current time
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const double reference_axial_rotation = reference_body.axial_rotation + reference_body.angular_frequency * universal_time;
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// Construct reference frame which transforms coordinates from inertial space to reference body BCBF space
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inertial_to_bcbf = physics::orbit::inertial::to_bcbf
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(
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reference_orbit.state.r,
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reference_orbit.elements.i,
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reference_body.axial_tilt,
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reference_axial_rotation
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);
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// Construct reference frame which transforms coordinates from inertial space to reference body topocentric space
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inertial_to_topocentric = inertial_to_bcbf * bcbf_to_topocentric;
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// Set the transform component translations of orbiting bodies to their topocentric positions
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registry.view<component::celestial_body, component::orbit, component::transform>().each(
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[&](entity::id entity_id, const auto& celestial_body, const auto& orbit, auto& transform)
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{
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// Transform Cartesian position vector (r) from inertial space to topocentric space
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const math::vector3<double> r_topocentric = inertial_to_topocentric * orbit.state.r;
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// Update local transform
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transform.local.translation = math::type_cast<float>(r_topocentric);
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});
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// Update blackbody lighting
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registry.view<component::celestial_body, component::orbit, component::blackbody>().each(
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[&](entity::id entity_id, const auto& celestial_body, const auto& orbit, const auto& blackbody)
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{
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// Calculate blackbody inertial basis
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double3 blackbody_forward_inertial = math::normalize(reference_orbit.state.r - orbit.state.r);
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double3 blackbody_up_inertial = {0, 0, 1};
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// Transform blackbody inertial position and basis into topocentric space
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double3 blackbody_position_topocentric = inertial_to_topocentric * orbit.state.r;
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double3 blackbody_forward_topocentric = inertial_to_topocentric.rotation * blackbody_forward_inertial;
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double3 blackbody_up_topocentric = inertial_to_topocentric.rotation * blackbody_up_inertial;
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// Calculate distance from observer to blackbody
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double blackbody_distance = math::length(blackbody_position_topocentric) - celestial_body.radius;
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// Calculate blackbody distance attenuation
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double distance_attenuation = 1.0 / (blackbody_distance * blackbody_distance);
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// Init atmospheric transmittance
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double3 atmospheric_transmittance = {1.0, 1.0, 1.0};
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// Get atmosphere component of reference body (if any)
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if (this->registry.has<entity::component::atmosphere>(reference_entity))
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{
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const entity::component::atmosphere& reference_atmosphere = registry.get<entity::component::atmosphere>(reference_entity);
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// Altitude of observer in meters
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geom::ray<double> sample_ray;
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sample_ray.origin = {0, reference_body.radius + observer_location[0], 0};
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sample_ray.direction = math::normalize(blackbody_position_topocentric);
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geom::sphere<double> exosphere;
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exosphere.center = {0, 0, 0};
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exosphere.radius = reference_body.radius + reference_atmosphere.exosphere_altitude;
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auto intersection_result = geom::ray_sphere_intersection(sample_ray, exosphere);
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if (std::get<0>(intersection_result))
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{
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double3 sample_start = sample_ray.origin;
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double3 sample_end = sample_ray.extrapolate(std::get<2>(intersection_result));
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double optical_depth_r = physics::atmosphere::optical_depth(sample_start, sample_end, reference_body.radius, reference_atmosphere.rayleigh_scale_height, 32);
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double optical_depth_k = physics::atmosphere::optical_depth(sample_start, sample_end, reference_body.radius, reference_atmosphere.mie_scale_height, 32);
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double optical_depth_o = 0.0;
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atmospheric_transmittance = transmittance(optical_depth_r, optical_depth_k, optical_depth_o, reference_atmosphere.rayleigh_scattering, reference_atmosphere.mie_scattering);
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}
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}
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if (sun_light != nullptr)
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{
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// Update blackbody light transform
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sun_light->set_translation(math::normalize(math::type_cast<float>(blackbody_position_topocentric)));
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sun_light->set_rotation
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(
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math::look_rotation
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(
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math::type_cast<float>(blackbody_forward_topocentric),
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math::type_cast<float>(blackbody_up_topocentric)
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)
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);
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// Sun color at the outer atmosphere
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float3 sun_color_outer = math::type_cast<float>(blackbody.luminous_intensity * distance_attenuation);
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// Sun color at sea level
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float3 sun_color_inner = math::type_cast<float>(blackbody.luminous_intensity * distance_attenuation * atmospheric_transmittance);
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// Update blackbody light color and intensity
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sun_light->set_color(sun_color_inner);
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sun_light->set_intensity(1.0f);
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// Upload blackbody params to sky pass
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if (this->sky_pass)
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{
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this->sky_pass->set_sun_position(math::type_cast<float>(blackbody_position_topocentric));
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this->sky_pass->set_sun_color(sun_color_outer, sun_color_inner);
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double blackbody_angular_radius = std::asin((celestial_body.radius * 2.0) / (blackbody_distance * 2.0));
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this->sky_pass->set_sun_angular_radius(static_cast<float>(blackbody_angular_radius));
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}
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}
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});
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// Update sky pass topocentric frame
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if (sky_pass != nullptr)
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{
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// Upload topocentric frame to sky pass
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sky_pass->set_topocentric_frame
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(
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physics::frame<float>
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{
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math::type_cast<float>(inertial_to_topocentric.translation),
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math::type_cast<float>(inertial_to_topocentric.rotation)
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}
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);
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// Upload observer altitude to sky pass
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sky_pass->set_observer_altitude(observer_location[0]);
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// Upload atmosphere params to sky pass
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if (registry.has<entity::component::atmosphere>(reference_entity))
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{
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const entity::component::atmosphere& reference_atmosphere = registry.get<entity::component::atmosphere>(reference_entity);
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sky_pass->set_scale_heights(reference_atmosphere.rayleigh_scale_height, reference_atmosphere.mie_scale_height);
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sky_pass->set_scattering_coefficients(math::type_cast<float>(reference_atmosphere.rayleigh_scattering), math::type_cast<float>(reference_atmosphere.mie_scattering));
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sky_pass->set_mie_anisotropy(reference_atmosphere.mie_anisotropy);
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sky_pass->set_atmosphere_radii(reference_body.radius, reference_body.radius + reference_atmosphere.exosphere_altitude);
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}
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}
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}
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void astronomy::set_universal_time(double time)
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{
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universal_time = time;
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}
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void astronomy::set_time_scale(double scale)
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{
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time_scale = scale;
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}
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void astronomy::set_reference_body(entity::id entity_id)
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{
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reference_entity = entity_id;
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update_bcbf_to_topocentric();
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}
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void astronomy::set_observer_location(const double3& location)
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{
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observer_location = location;
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update_bcbf_to_topocentric();
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}
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void astronomy::set_sun_light(scene::directional_light* light)
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{
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sun_light = light;
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}
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void astronomy::set_sky_pass(::render::sky_pass* pass)
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{
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this->sky_pass = pass;
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}
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void astronomy::on_celestial_body_construct(entity::registry& registry, entity::id entity_id, entity::component::celestial_body& celestial_body)
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{
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if (entity_id == reference_entity)
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update_bcbf_to_topocentric();
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}
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void astronomy::on_celestial_body_replace(entity::registry& registry, entity::id entity_id, entity::component::celestial_body& celestial_body)
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{
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if (entity_id == reference_entity)
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update_bcbf_to_topocentric();
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}
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void astronomy::update_bcbf_to_topocentric()
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{
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double radial_distance = observer_location[0];
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if (reference_entity)
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{
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if (registry.has<entity::component::celestial_body>(reference_entity))
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radial_distance += registry.get<entity::component::celestial_body>(reference_entity).radius;
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}
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// Construct reference frame which transforms coordinates from BCBF space to topocentric space
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bcbf_to_topocentric = physics::orbit::bcbf::to_topocentric
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(
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radial_distance,
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observer_location[1],
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observer_location[2]
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) * sez_to_ezs;
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}
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} // namespace system
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} // namespace entity
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