rigid-body.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 <engine/physics/kinematics/rigid-body.hpp>
#include <engine/math/interpolation.hpp>
#include <algorithm>
 
namespace physics {
 
void rigid_body::integrate_forces(float dt) noexcept
{
    // Apply forces
    m_linear_momentum += m_applied_force * dt;
    m_angular_momentum += m_applied_torque * dt;
    
    // Apply damping
    m_linear_momentum *= std::max<float>(0.0f, 1.0f - m_linear_damping * dt);
    m_angular_momentum *= std::max<float>(0.0f, 1.0f - m_angular_damping * dt);
    
    // Update velocities
    m_linear_velocity = m_inverse_mass * m_linear_momentum;
    m_angular_velocity = m_inverse_inertia * m_angular_momentum;
    
    // Clear forces
    m_applied_force = math::fvec3::zero();
    m_applied_torque = math::fvec3::zero();
}
 
void rigid_body::integrate_velocities(float dt) noexcept
{
    // Record previous state
    m_previous_transform = m_current_transform;
    
    // Update position
    m_current_transform.translation += m_linear_velocity * dt;
    
    // Update orientation
    const math::fquat spin = math::fquat{0.0f, m_angular_velocity * 0.5f} * m_current_transform.rotation;
    m_current_transform.rotation = math::normalize(m_current_transform.rotation + spin * dt);
}
 
math::transform<float> rigid_body::interpolate(float alpha) const
{
    return
    {
        math::lerp(m_previous_transform.translation, m_current_transform.translation, alpha),
        math::nlerp(m_previous_transform.rotation, m_current_transform.rotation, alpha),
        math::lerp(m_previous_transform.scale, m_current_transform.scale, alpha),
    };
}
 
} // namespace physics