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