atmosphere-system.cpp

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/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include "game/systems/atmosphere-system.hpp"
#include <engine/physics/gas/atmosphere.hpp>
#include <engine/physics/gas/ozone.hpp>
#include <engine/physics/number-density.hpp>
 
atmosphere_system::atmosphere_system(entity::registry& registry):
    updatable_system(registry)
{
    registry.on_construct<::atmosphere_component>().connect<&atmosphere_system::on_atmosphere_construct>(this);
    registry.on_update<::atmosphere_component>().connect<&atmosphere_system::on_atmosphere_update>(this);
    registry.on_destroy<::atmosphere_component>().connect<&atmosphere_system::on_atmosphere_destroy>(this);
    
    set_rgb_wavelengths({680, 550, 440});
}
 
atmosphere_system::~atmosphere_system()
{
    registry.on_construct<::atmosphere_component>().disconnect<&atmosphere_system::on_atmosphere_construct>(this);
    registry.on_update<::atmosphere_component>().disconnect<&atmosphere_system::on_atmosphere_update>(this);
    registry.on_destroy<::atmosphere_component>().disconnect<&atmosphere_system::on_atmosphere_destroy>(this);
}
 
void atmosphere_system::update(float t, float dt)
{}
 
void atmosphere_system::set_rgb_wavelengths(const math::dvec3& wavelengths)
{
    m_rgb_wavelengths_nm = wavelengths;
    m_rgb_wavelengths_m = m_rgb_wavelengths_nm * 1e-9;
    
    // Update ozone cross sections
    m_rgb_ozone_cross_sections =
    {
        physics::gas::ozone::cross_section_293k<double>(m_rgb_wavelengths_nm.x()),
        physics::gas::ozone::cross_section_293k<double>(m_rgb_wavelengths_nm.y()),
        physics::gas::ozone::cross_section_293k<double>(m_rgb_wavelengths_nm.z())
    };
    
    // Update atmosphere components
    registry.view<::atmosphere_component>().each
    (
        [&](entity::id entity_id, auto& component)
        {
            update_atmosphere(entity_id);
        }
    );
}
 
void atmosphere_system::set_sky_pass(::render::sky_pass* pass)
{
    m_sky_pass = pass;
    update_sky_pass();
}
 
void atmosphere_system::set_active_atmosphere(entity::id entity_id)
{
    if (entity_id != m_active_atmosphere_eid)
    {
        m_active_atmosphere_eid = entity_id;
        update_sky_pass();
    }
}
 
void atmosphere_system::update_atmosphere(entity::id entity_id)
{
    // Get atmosphere component of the entity
    ::atmosphere_component* component = registry.try_get<::atmosphere_component>(entity_id);
    
    // Abort if entity has no atmosphere component
    if (!component)
    {
        return;
    }
    
    // Calculate Rayleigh scattering coefficients
    const double rayleigh_density = physics::number_density(component->rayleigh_concentration);
    const double rayleigh_polarization = physics::gas::atmosphere::polarization(component->index_of_refraction, rayleigh_density);
    component->rayleigh_scattering =
    {
        physics::gas::atmosphere::scattering(rayleigh_density, rayleigh_polarization, m_rgb_wavelengths_m.x()),
        physics::gas::atmosphere::scattering(rayleigh_density, rayleigh_polarization, m_rgb_wavelengths_m.y()),
        physics::gas::atmosphere::scattering(rayleigh_density, rayleigh_polarization, m_rgb_wavelengths_m.z())
    };
    
    // Calculate Mie scattering and extinction coefficients
    const double mie_density = physics::number_density(component->mie_concentration);
    const double mie_polarization = physics::gas::atmosphere::polarization(component->index_of_refraction, mie_density);
    component->mie_scattering = physics::gas::atmosphere::scattering(mie_density, mie_polarization);
    component->mie_extinction = physics::gas::atmosphere::extinction(component->mie_scattering, component->mie_albedo);
    
    // Calculate ozone absorption coefficients
    const double ozone_density = physics::number_density(component->ozone_concentration);
    component->ozone_absorption =
    {
        physics::gas::ozone::absorption(m_rgb_ozone_cross_sections.x(), ozone_density),
        physics::gas::ozone::absorption(m_rgb_ozone_cross_sections.y(), ozone_density),
        physics::gas::ozone::absorption(m_rgb_ozone_cross_sections.z(), ozone_density)
    };
    
    // Update sky pass parameters
    if (entity_id == m_active_atmosphere_eid)
    {
        update_sky_pass();
    }
}
 
void atmosphere_system::update_sky_pass()
{
    // Abort if no sky pass set
    if (!m_sky_pass)
    {
        return;
    }
    
    // Abort if active atmosphere entity is not valid
    if (!registry.valid(m_active_atmosphere_eid))
    {
        return;
    }
    
    // Get atmosphere component of the entity
    ::atmosphere_component* component = registry.try_get<::atmosphere_component>(m_active_atmosphere_eid);
    
    // Abort if entity has no atmosphere component
    if (!component)
    {
        return;
    }
    
    m_sky_pass->set_atmosphere_upper_limit(static_cast<float>(component->upper_limit));
    m_sky_pass->set_rayleigh_parameters(static_cast<float>(component->rayleigh_scale_height), math::fvec3(component->rayleigh_scattering));
    m_sky_pass->set_mie_parameters(static_cast<float>(component->mie_scale_height), static_cast<float>(component->mie_scattering), static_cast<float>(component->mie_extinction), static_cast<float>(component->mie_anisotropy));
    m_sky_pass->set_ozone_parameters(static_cast<float>(component->ozone_lower_limit), static_cast<float>(component->ozone_upper_limit), static_cast<float>(component->ozone_mode), math::fvec3(component->ozone_absorption));
    m_sky_pass->set_airglow_luminance(math::fvec3(component->airglow_luminance));
}
 
void atmosphere_system::on_atmosphere_construct(entity::registry& registry, entity::id entity_id)
{
    update_atmosphere(entity_id);
}
 
void atmosphere_system::on_atmosphere_update(entity::registry& registry, entity::id entity_id)
{
    update_atmosphere(entity_id);
}
 
void atmosphere_system::on_atmosphere_destroy(entity::registry& registry, entity::id entity_id)
{
    if (entity_id == m_active_atmosphere_eid)
    {
        m_active_atmosphere_eid = entt::null;
    }
}