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@maximilliangeorge
Last active April 9, 2020 15:07
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After Effects Expressions
// MOMENTUM SCROLLING
//
// Nice easings without the hassle. Doesn't work well for very long distances.
//
// 1. Separate dimensions on layer to scroll (right click _> separate dimensions)
// 2. Apply the expression to the layers Y Position
// 3. Add keyframes. Easing will adapt to mimic momentum scrolling.
const c = thisLayer("Transform")("Y Position")
var NEWTON_ITERATIONS = 4;
var NEWTON_MIN_SLOPE = 0.001;
var SUBDIVISION_PRECISION = 0.0000001;
var SUBDIVISION_MAX_ITERATIONS = 10;
var kSplineTableSize = 11;
var kSampleStepSize = 1.0 / (kSplineTableSize - 1.0);
var float32ArraySupported = typeof Float32Array === 'function';
function A (aA1, aA2) { return 1.0 - 3.0 * aA2 + 3.0 * aA1; }
function B (aA1, aA2) { return 3.0 * aA2 - 6.0 * aA1; }
function C (aA1) { return 3.0 * aA1; }
function calcBezier (aT, aA1, aA2) { return ((A(aA1, aA2) * aT + B(aA1, aA2)) * aT + C(aA1)) * aT; }
function getSlope (aT, aA1, aA2) { return 3.0 * A(aA1, aA2) * aT * aT + 2.0 * B(aA1, aA2) * aT + C(aA1); }
function binarySubdivide (aX, aA, aB, mX1, mX2) {
var currentX, currentT, i = 0
do {
currentT = aA + (aB - aA) / 2.0
currentX = calcBezier(currentT, mX1, mX2) - aX
if (currentX > 0.0) {
aB = currentT
} else {
aA = currentT
}
} while (Math.abs(currentX) > SUBDIVISION_PRECISION && ++i < SUBDIVISION_MAX_ITERATIONS);
return currentT;
}
function newtonRaphsonIterate (aX, aGuessT, mX1, mX2) {
for (var i = 0; i < NEWTON_ITERATIONS; ++i) {
var currentSlope = getSlope(aGuessT, mX1, mX2)
if (currentSlope === 0.0) {
return aGuessT
}
var currentX = calcBezier(aGuessT, mX1, mX2) - aX
aGuessT -= currentX / currentSlope
}
return aGuessT
}
function LinearEasing (x) {
return x
}
function bezier(mX1, mY1, mX2, mY2) {
if (!(0 <= mX1 && mX1 <= 1 && 0 <= mX2 && mX2 <= 1)) {
throw new Error('bezier x values must be in [0, 1] range')
}
if (mX1 === mY1 && mX2 === mY2) {
return LinearEasing
}
var sampleValues = float32ArraySupported ? new Float32Array(kSplineTableSize) : new Array(kSplineTableSize)
for (var i = 0; i < kSplineTableSize; ++i) {
sampleValues[i] = calcBezier(i * kSampleStepSize, mX1, mX2)
}
function getTForX (aX) {
var intervalStart = 0.0
var currentSample = 1
var lastSample = kSplineTableSize - 1
for (; currentSample !== lastSample && sampleValues[currentSample] <= aX; ++currentSample) {
intervalStart += kSampleStepSize
}
--currentSample
// Interpolate to provide an initial guess for t
var dist = (aX - sampleValues[currentSample]) / (sampleValues[currentSample + 1] - sampleValues[currentSample])
var guessForT = intervalStart + dist * kSampleStepSize
var initialSlope = getSlope(guessForT, mX1, mX2)
if (initialSlope >= NEWTON_MIN_SLOPE) {
return newtonRaphsonIterate(aX, guessForT, mX1, mX2)
} else if (initialSlope === 0.0) {
return guessForT;
} else {
return binarySubdivide(aX, intervalStart, intervalStart + kSampleStepSize, mX1, mX2);
}
}
return function BezierEasing (x) {
if (x === 0 || x === 1) {
return x
}
return calcBezier(getTForX(x), mY1, mY2)
}
}
try {
let index = c.numKeys
while (c.key(index).time > time) {
index--
}
const transform = (value, range1, range2) => {
return ( (value - range1[0]) / (range1[1] - range1[0]) ) * (range2[1] - range2[0]) + range2[0]
}
const k1 = c.key(index)
const k2 = c.key(index + 1)
const progress = (time - k1.time) / (k2.time - k1.time)
const duration = k2.time - k1.time
const distance = Math.abs(k2.value - k1.value)
const pxFactor = 1800
const magnitude = duration * pxFactor / distance
const attack = 0.11 * magnitude
const ease = 1 - attack
const easing = bezier(attack, 0, attack / 1.5, 1)
transform(easing(progress), [0, 1], [k1.value, k2.value])
} catch (e) {
value
}
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