collision-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/collision-system.hpp"
#include "game/components/transform-component.hpp"
#include "game/components/picking-component.hpp"
#include "game/components/rigid-body-component.hpp"
#include <engine/geom/intersection.hpp>
#include <engine/geom/primitives/plane.hpp>
#include <limits>
 
 
collision_system::collision_system(entity::registry& registry):
    updatable_system(registry)
{
}
 
collision_system::~collision_system()
{
}
 
void collision_system::update(float t, float dt)
{
 
}
 
entity::id collision_system::pick_nearest(const geom::ray<float, 3>& ray, std::uint32_t flags) const
{
    entity::id nearest_eid = entt::null;
    float nearest_distance = std::numeric_limits<float>::infinity();
    
    // For each entity with picking and transform components
    registry.view<picking_component, transform_component>().each
    (
        [&](entity::id entity_id, const auto& picking, const auto& transform)
        {
            // Skip entity if picking flags don't match
            if (!~(flags | picking.flags))
                return;
            
            // Transform picking sphere
            const geom::sphere<float> sphere =
            {
                transform.world * picking.sphere.center,
                picking.sphere.radius * math::max(transform.world.scale)
            };
            
            // Test for intersection between ray and sphere
            auto result = geom::intersection(ray, sphere);
            if (result)
            {
                float t0 = std::get<0>(*result);
                float t1 = std::get<1>(*result);
                
                if (t0 < nearest_distance)
                {
                    nearest_eid = entity_id;
                    nearest_distance = t0;
                }
            }
        }
    );
    
    return nearest_eid;
}
 
entity::id collision_system::pick_nearest(const math::fvec3& origin, const math::fvec3& normal, std::uint32_t flags) const
{
    entity::id nearest_eid = entt::null;
    float nearest_sqr_distance = std::numeric_limits<float>::infinity();
    
    // Construct picking plane
    const geom::plane<float> picking_plane = geom::plane<float>(origin, normal);
    
    // For each entity with picking and transform components
    registry.view<picking_component, transform_component>().each
    (
        [&](entity::id entity_id, const auto& picking, const auto& transform)
        {
            // Skip entity if picking flags don't match
            if (!~(flags | picking.flags))
                return;
            
            // Transform picking sphere center
            math::fvec3 picking_sphere_center = transform.world * picking.sphere.center;
            
            // Skip entity if picking sphere center has negative distance from picking plane
            if (picking_plane.distance(picking_sphere_center) < 0.0f)
                return;
            
            // Measure distance from picking plane origin to picking sphere center
            const float sqr_distance = math::sqr_distance(picking_sphere_center, origin);
            
            // Check if entity is nearer than the current nearest entity
            if (sqr_distance < nearest_sqr_distance)
            {
                nearest_eid = entity_id;
                nearest_sqr_distance = sqr_distance;
            }
        }
    );
    
    return nearest_eid;
}