Marc Mintel
5397309103
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52 lines
1.9 KiB
Plaintext
52 lines
1.9 KiB
Plaintext
import { noop } from 'motion-utils';
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/*
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Bezier function generator
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This has been modified from Gaëtan Renaudeau's BezierEasing
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https://github.com/gre/bezier-easing/blob/master/src/index.js
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https://github.com/gre/bezier-easing/blob/master/LICENSE
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I've removed the newtonRaphsonIterate algo because in benchmarking it
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wasn't noticiably faster than binarySubdivision, indeed removing it
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usually improved times, depending on the curve.
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I also removed the lookup table, as for the added bundle size and loop we're
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only cutting ~4 or so subdivision iterations. I bumped the max iterations up
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to 12 to compensate and this still tended to be faster for no perceivable
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loss in accuracy.
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Usage
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const easeOut = cubicBezier(.17,.67,.83,.67);
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const x = easeOut(0.5); // returns 0.627...
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*/
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// Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
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const calcBezier = (t, a1, a2) => (((1.0 - 3.0 * a2 + 3.0 * a1) * t + (3.0 * a2 - 6.0 * a1)) * t + 3.0 * a1) *
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t;
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const subdivisionPrecision = 0.0000001;
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const subdivisionMaxIterations = 12;
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function binarySubdivide(x, lowerBound, upperBound, mX1, mX2) {
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let currentX;
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let currentT;
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let i = 0;
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do {
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currentT = lowerBound + (upperBound - lowerBound) / 2.0;
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currentX = calcBezier(currentT, mX1, mX2) - x;
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if (currentX > 0.0) {
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upperBound = currentT;
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}
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else {
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lowerBound = currentT;
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}
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} while (Math.abs(currentX) > subdivisionPrecision &&
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++i < subdivisionMaxIterations);
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return currentT;
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}
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function cubicBezier(mX1, mY1, mX2, mY2) {
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// If this is a linear gradient, return linear easing
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if (mX1 === mY1 && mX2 === mY2)
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return noop;
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const getTForX = (aX) => binarySubdivide(aX, 0, 1, mX1, mX2);
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// If animation is at start/end, return t without easing
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return (t) => t === 0 || t === 1 ? t : calcBezier(getTForX(t), mY1, mY2);
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}
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export { cubicBezier };
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