@shopify/react-native-skia/lib/commonjs/animation/decay/decay.js

High-performance React Native Graphics using Skia

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.decay = void 0;
const VELOCITY_EPS = 1;
const SLOPE_FACTOR = 0.1;

const decay = (now, state, config) => {
  const {
    lastTimestamp,
    startTimestamp,
    initialVelocity,
    current,
    velocity
  } = state;
  const nextState = { ...state
  };
  const deltaTime = Math.min(now - lastTimestamp, 64);
  const v = velocity * Math.exp(-(1 - config.deceleration) * (now - startTimestamp) * SLOPE_FACTOR);
  nextState.current = current + v * config.velocityFactor * deltaTime / 1000; // /1000 because time is in ms not in s

  nextState.velocity = v;
  nextState.lastTimestamp = now;

  if (config.clamp) {
    if (initialVelocity < 0 && nextState.current <= config.clamp[0]) {
      nextState.current = config.clamp[0];
      nextState.finished = true;
    } else if (initialVelocity > 0 && nextState.current >= config.clamp[1]) {
      nextState.current = config.clamp[1];
      nextState.finished = true;
    }
  }

  nextState.finished = Math.abs(v) < VELOCITY_EPS;
  return nextState;
};

exports.decay = decay;
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