/* * Copyright (C) 2016 Apple Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF * THE POSSIBILITY OF SUCH DAMAGE. */ #pragma once namespace WebCore { class SpringSolver { public: SpringSolver(double mass, double stiffness, double damping, double initialVelocity) { m_w0 = std::sqrt(stiffness / mass); m_zeta = damping / (2 * std::sqrt(stiffness * mass)); if (m_zeta < 1) { // Under-damped. m_wd = m_w0 * std::sqrt(1 - m_zeta * m_zeta); m_A = 1; m_B = (m_zeta * m_w0 + -initialVelocity) / m_wd; } else { // Critically damped (ignoring over-damped case for now). m_A = 1; m_B = -initialVelocity + m_w0; } } double solve(double t) { if (m_zeta < 1) { // Under-damped t = std::exp(-t * m_zeta * m_w0) * (m_A * std::cos(m_wd * t) + m_B * std::sin(m_wd * t)); } else { // Critically damped (ignoring over-damped case for now). t = (m_A + m_B * t) * std::exp(-t * m_w0); } // Map range from [1..0] to [0..1]. return 1 - t; } private: double m_w0; double m_zeta; double m_wd; double m_A; double m_B; }; } // namespace WebCore