vuescroll/src/third-party/scroller/animate.js

A beautiful scrollbar based on Vue.js for PC and mobile.

/*
 * Scroller
 * http://github.com/zynga/scroller
 *
 * Copyright 2011, Zynga Inc.
 * Licensed under the MIT License.
 * https://raw.github.com/zynga/scroller/master/MIT-LICENSE.txt
 *
 * Based on the work of: Unify Project (unify-project.org)
 * http://unify-project.org
 * Copyright 2011, Deutsche Telekom AG
 * License: MIT + Apache (V2)
 */

/**
 * Generic animation class with support for dropped frames both optional easing and duration.
 *
 * Optional duration is useful when the lifetime is defined by another condition than time
 * e.g. speed of an animating object, etc.
 *
 * Dropped frame logic allows to keep using the same updater logic independent from the actual
 * rendering. This eases a lot of cases where it might be pretty complex to break down a state
 * based on the pure time difference.
 */
import { requestAnimationFrame } from './requestAnimationFrame';

var time =
  Date.now ||
  function() {
    return +new Date();
  };
var desiredFrames = 60;
var millisecondsPerSecond = 1000;
var running = {};
var counter = 1;

const core = { effect: {} };
let global = null;

if (typeof window !== 'undefined') {
  global = window;
} else {
  global = {};
}

core.effect.Animate = {
  /**
   * A requestAnimationFrame wrapper / polyfill.
   *
   * @param callback {Function} The callback to be invoked before the next repaint.
   * @param root {HTMLElement} The root element for the repaint
   */
  requestAnimationFrame: requestAnimationFrame(global),
  /**
   * Stops the given animation.
   *
   * @param id {Integer} Unique animation ID
   * @return {Boolean} Whether the animation was stopped (aka, was running before)
   */
  stop: function(id) {
    var cleared = running[id] != null;
    if (cleared) {
      running[id] = null;
    }

    return cleared;
  },

  /**
   * Whether the given animation is still running.
   *
   * @param id {Integer} Unique animation ID
   * @return {Boolean} Whether the animation is still running
   */
  isRunning: function(id) {
    return running[id] != null;
  },

  /**
   * Start the animation.
   *
   * @param stepCallback {Function} Pointer to function which is executed on every step.
   *   Signature of the method should be `function(percent, now, virtual) { return continueWithAnimation; }`
   * @param verifyCallback {Function} Executed before every animation step.
   *   Signature of the method should be `function() { return continueWithAnimation; }`
   * @param completedCallback {Function}
   *   Signature of the method should be `function(droppedFrames, finishedAnimation) {}`
   * @param duration {Integer} Milliseconds to run the animation
   * @param easingMethod {Function} Pointer to easing function
   *   Signature of the method should be `function(percent) { return modifiedValue; }`
   * @param root {Element ? document.body} Render root, when available. Used for internal
   *   usage of requestAnimationFrame.
   * @return {Integer} Identifier of animation. Can be used to stop it any time.
   */
  start: function(
    stepCallback,
    verifyCallback,
    completedCallback,
    duration,
    easingMethod,
    root
  ) {
    var start = time();
    var lastFrame = start;
    var percent = 0;
    var dropCounter = 0;
    var id = counter++;

    if (!root) {
      root = document.body;
    }

    // Compacting running db automatically every few new animations
    if (id % 20 === 0) {
      var newRunning = {};
      for (var usedId in running) {
        newRunning[usedId] = true;
      }
      running = newRunning;
    }

    // This is the internal step method which is called every few milliseconds
    var step = function(virtual) {
      // Normalize virtual value
      var render = virtual !== true;

      // Get current time
      var now = time();

      // Verification is executed before next animation step
      if (!running[id] || (verifyCallback && !verifyCallback(id))) {
        running[id] = null;
        completedCallback &&
          completedCallback(
            desiredFrames -
              dropCounter / ((now - start) / millisecondsPerSecond),
            id,
            false
          );
        return;
      }

      // For the current rendering to apply let's update omitted steps in memory.
      // This is important to bring internal state variables up-to-date with progress in time.
      if (render) {
        var droppedFrames =
          Math.round(
            (now - lastFrame) / (millisecondsPerSecond / desiredFrames)
          ) - 1;
        for (var j = 0; j < Math.min(droppedFrames, 4); j++) {
          step(true);
          dropCounter++;
        }
      }

      // Compute percent value
      if (duration) {
        percent = (now - start) / duration;
        if (percent > 1) {
          percent = 1;
        }
      }

      // Execute step callback, then...
      var value = easingMethod ? easingMethod(percent) : percent;
      if (
        (stepCallback(value, now, render) === false || percent === 1) &&
        render
      ) {
        running[id] = null;
        completedCallback &&
          completedCallback(
            desiredFrames -
              dropCounter / ((now - start) / millisecondsPerSecond),
            id,
            percent === 1 || duration == null
          );
      } else if (render) {
        lastFrame = now;
        core.effect.Animate.requestAnimationFrame(step, root);
      }
    };

    // Mark as running
    running[id] = true;

    // Init first step
    core.effect.Animate.requestAnimationFrame(step, root);

    // Return unique animation ID
    return id;
  }
};

export { core };