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framer-motion

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A simple and powerful JavaScript animation library

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import { warning, secondsToMilliseconds, millisecondsToSeconds } from 'motion-utils'; import { clamp } from '../../../utils/clamp.mjs'; import { springDefaults } from './defaults.mjs'; const safeMin = 0.001; function findSpring({ duration = springDefaults.duration, bounce = springDefaults.bounce, velocity = springDefaults.velocity, mass = springDefaults.mass, }) { let envelope; let derivative; warning(duration <= secondsToMilliseconds(springDefaults.maxDuration), "Spring duration must be 10 seconds or less"); let dampingRatio = 1 - bounce; /** * Restrict dampingRatio and duration to within acceptable ranges. */ dampingRatio = clamp(springDefaults.minDamping, springDefaults.maxDamping, dampingRatio); duration = clamp(springDefaults.minDuration, springDefaults.maxDuration, millisecondsToSeconds(duration)); if (dampingRatio < 1) { /** * Underdamped spring */ envelope = (undampedFreq) => { const exponentialDecay = undampedFreq * dampingRatio; const delta = exponentialDecay * duration; const a = exponentialDecay - velocity; const b = calcAngularFreq(undampedFreq, dampingRatio); const c = Math.exp(-delta); return safeMin - (a / b) * c; }; derivative = (undampedFreq) => { const exponentialDecay = undampedFreq * dampingRatio; const delta = exponentialDecay * duration; const d = delta * velocity + velocity; const e = Math.pow(dampingRatio, 2) * Math.pow(undampedFreq, 2) * duration; const f = Math.exp(-delta); const g = calcAngularFreq(Math.pow(undampedFreq, 2), dampingRatio); const factor = -envelope(undampedFreq) + safeMin > 0 ? -1 : 1; return (factor * ((d - e) * f)) / g; }; } else { /** * Critically-damped spring */ envelope = (undampedFreq) => { const a = Math.exp(-undampedFreq * duration); const b = (undampedFreq - velocity) * duration + 1; return -safeMin + a * b; }; derivative = (undampedFreq) => { const a = Math.exp(-undampedFreq * duration); const b = (velocity - undampedFreq) * (duration * duration); return a * b; }; } const initialGuess = 5 / duration; const undampedFreq = approximateRoot(envelope, derivative, initialGuess); duration = secondsToMilliseconds(duration); if (isNaN(undampedFreq)) { return { stiffness: springDefaults.stiffness, damping: springDefaults.damping, duration, }; } else { const stiffness = Math.pow(undampedFreq, 2) * mass; return { stiffness, damping: dampingRatio * 2 * Math.sqrt(mass * stiffness), duration, }; } } const rootIterations = 12; function approximateRoot(envelope, derivative, initialGuess) { let result = initialGuess; for (let i = 1; i < rootIterations; i++) { result = result - envelope(result) / derivative(result); } return result; } function calcAngularFreq(undampedFreq, dampingRatio) { return undampedFreq * Math.sqrt(1 - dampingRatio * dampingRatio); } export { calcAngularFreq, findSpring };