1/*
2 * Copyright (C) 2016 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28namespace WebCore {
29
30class SpringSolver {
31public:
32 SpringSolver(double mass, double stiffness, double damping, double initialVelocity)
33 {
34 m_w0 = std::sqrt(stiffness / mass);
35 m_zeta = damping / (2 * std::sqrt(stiffness * mass));
36
37 if (m_zeta < 1) {
38 // Under-damped.
39 m_wd = m_w0 * std::sqrt(1 - m_zeta * m_zeta);
40 m_A = 1;
41 m_B = (m_zeta * m_w0 + -initialVelocity) / m_wd;
42 } else {
43 // Critically damped (ignoring over-damped case for now).
44 m_A = 1;
45 m_B = -initialVelocity + m_w0;
46 }
47 }
48
49 double solve(double t)
50 {
51 if (m_zeta < 1) {
52 // Under-damped
53 t = std::exp(-t * m_zeta * m_w0) * (m_A * std::cos(m_wd * t) + m_B * std::sin(m_wd * t));
54 } else {
55 // Critically damped (ignoring over-damped case for now).
56 t = (m_A + m_B * t) * std::exp(-t * m_w0);
57 }
58
59 // Map range from [1..0] to [0..1].
60 return 1 - t;
61 }
62
63private:
64 double m_w0;
65 double m_zeta;
66 double m_wd;
67 double m_A;
68 double m_B;
69};
70
71} // namespace WebCore
72