Adolfo Reyna
114 lines
3.8 KiB
JavaScript
114 lines
3.8 KiB
JavaScript
"use strict";
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// Taken from https://github.com/facebook/react-native/blob/0b9ea60b4fee8cacc36e7160e31b91fc114dbc0d/Libraries/Animated/src/bezier.js
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.bezier = bezier;
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const NEWTON_ITERATIONS = 4;
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const NEWTON_MIN_SLOPE = 0.001;
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const SUBDIVISION_PRECISION = 0.0000001;
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const SUBDIVISION_MAX_ITERATIONS = 10;
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const kSplineTableSize = 11;
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const kSampleStepSize = 1.0 / (kSplineTableSize - 1.0);
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const float32ArraySupported = typeof Float32Array === 'function';
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function a(aA1, aA2) {
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return 1.0 - 3.0 * aA2 + 3.0 * aA1;
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}
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function b(aA1, aA2) {
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return 3.0 * aA2 - 6.0 * aA1;
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}
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function c(aA1) {
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return 3.0 * aA1;
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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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function calcBezier(aT, aA1, aA2) {
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return ((a(aA1, aA2) * aT + b(aA1, aA2)) * aT + c(aA1)) * aT;
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}
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// Returns dx/dt given t, x1, and x2, or dy/dt given t, y1, and y2.
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function getSlope(aT, aA1, aA2) {
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return 3.0 * a(aA1, aA2) * aT * aT + 2.0 * b(aA1, aA2) * aT + c(aA1);
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}
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function binarySubdivide({ aX, _aA, _aB, 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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let aA = _aA;
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let aB = _aB;
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do {
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currentT = aA + (aB - aA) / 2.0;
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currentX = calcBezier(currentT, mX1, mX2) - aX;
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if (currentX > 0.0) {
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aB = currentT;
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}
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else {
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aA = currentT;
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}
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} while (Math.abs(currentX) > SUBDIVISION_PRECISION &&
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++i < SUBDIVISION_MAX_ITERATIONS);
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return currentT;
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}
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function newtonRaphsonIterate(aX, _aGuessT, mX1, mX2) {
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let aGuessT = _aGuessT;
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for (let i = 0; i < NEWTON_ITERATIONS; ++i) {
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const currentSlope = getSlope(aGuessT, mX1, mX2);
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if (currentSlope === 0.0) {
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return aGuessT;
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}
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const currentX = calcBezier(aGuessT, mX1, mX2) - aX;
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aGuessT -= currentX / currentSlope;
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}
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return aGuessT;
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}
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function bezier(mX1, mY1, mX2, mY2) {
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if (!(mX1 >= 0 && mX1 <= 1 && mX2 >= 0 && mX2 <= 1)) {
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throw new Error('bezier x values must be in [0, 1] range');
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}
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// Precompute samples table
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const sampleValues = float32ArraySupported
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? new Float32Array(kSplineTableSize)
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: new Array(kSplineTableSize);
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if (mX1 !== mY1 || mX2 !== mY2) {
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for (let i = 0; i < kSplineTableSize; ++i) {
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sampleValues[i] = calcBezier(i * kSampleStepSize, mX1, mX2);
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}
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}
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function getTForX(aX) {
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let intervalStart = 0.0;
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let currentSample = 1;
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const lastSample = kSplineTableSize - 1;
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for (; currentSample !== lastSample && sampleValues[currentSample] <= aX; ++currentSample) {
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intervalStart += kSampleStepSize;
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}
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--currentSample;
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// Interpolate to provide an initial guess for t
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const dist = (aX - sampleValues[currentSample]) /
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(sampleValues[currentSample + 1] - sampleValues[currentSample]);
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const guessForT = intervalStart + dist * kSampleStepSize;
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const initialSlope = getSlope(guessForT, mX1, mX2);
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if (initialSlope >= NEWTON_MIN_SLOPE) {
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return newtonRaphsonIterate(aX, guessForT, mX1, mX2);
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}
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if (initialSlope === 0.0) {
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return guessForT;
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}
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return binarySubdivide({
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aX,
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_aA: intervalStart,
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_aB: intervalStart + kSampleStepSize,
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mX1,
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mX2,
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});
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}
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return function (x) {
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if (mX1 === mY1 && mX2 === mY2) {
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return x; // linear
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}
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// Because JavaScript number are imprecise, we should guarantee the extremes are right.
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if (x === 0) {
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return 0;
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}
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if (x === 1) {
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return 1;
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}
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return calcBezier(getTForX(x), mY1, mY2);
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};
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}
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