Websites/webkit.org/blog-files/leaves/leaves.js

/*
Important:

This is sample code demonstrating API, technology or techniques in development.
Although this sample code has been reviewed for technical accuracy, it is not 
final. Apple is supplying this information to help you plan for the adoption of 
the technologies and programming interfaces described herein. This information 
is subject to change, and software implemented based on this sample code should 
be tested with final operating system software and final documentation. Newer 
versions of this sample code may be provided with future seeds of the API or 
technology. For information about updates to this and other developer 
documentation, view the New & Updated sidebars in subsequent documentation seeds.
*/

/*
File: Leaves.js
Abstract: Defines JavaScript functionality for the leaves sample.
          Creates all the leaves but do not animate them. Determines which
          spin animation should be applied to each leaf.
Version: 1.0

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*/


/* Define the number of leaves to be used in the animation */
const NUMBER_OF_LEAVES = 30;

/* 
    Called when the "Falling Leaves" page is completely loaded.
*/
function init()
{
    /* Get a reference to the element that will contain the leaves */
    var container = document.getElementById('leafContainer');
    /* Fill the empty container with new leaves */
    for (var i = 0; i < NUMBER_OF_LEAVES; i++) 
    {
        container.appendChild(createALeaf());
    }
}


/*
    Receives the lowest and highest values of a range and
    returns a random integer that falls within that range.
*/
function randomInteger(low, high)
{
    return low + Math.floor(Math.random() * (high - low));
}


/*
   Receives the lowest and highest values of a range and
   returns a random float that falls within that range.
*/
function randomFloat(low, high)
{
    return low + Math.random() * (high - low);
}


/*
    Receives a number and returns its CSS pixel value.
*/
function pixelValue(value)
{
    return value + 'px';
}


/*
    Returns a duration value for the falling animation.
*/

function durationValue(value)
{
    return value + 's';
}


/*
    Uses an img element to create each leaf. "Leaves.css" implements two spin 
    animations for the leaves: clockwiseSpin and counterclockwiseSpinAndFlip. This
    function determines which of these spin animations should be applied to each leaf.
    
*/
function createALeaf()
{
    /* Start by creating a wrapper div, and an empty img element */
    var leafDiv = document.createElement('div');
    var image = document.createElement('img');
    
    /* Randomly choose a leaf image and assign it to the newly created element */
    image.src = 'images/realLeaf' + randomInteger(1, 5) + '.png';
    
    leafDiv.style.top = "-100px";

    /* Position the leaf at a random location along the screen */
    leafDiv.style.left = pixelValue(randomInteger(0, 500));
    
    /* Randomly choose a spin animation */
    var spinAnimationName = (Math.random() < 0.5) ? 'clockwiseSpin' : 'counterclockwiseSpinAndFlip';
    
    /* Set the -webkit-animation-name property with these values */
    leafDiv.style.webkitAnimationName = 'fade, drop';
    image.style.webkitAnimationName = spinAnimationName;
    
    /* Figure out a random duration for the fade and drop animations */
    var fadeAndDropDuration = durationValue(randomFloat(5, 11));
    
    /* Figure out another random duration for the spin animation */
    var spinDuration = durationValue(randomFloat(4, 8));
    /* Set the -webkit-animation-duration property with these values */
    leafDiv.style.webkitAnimationDuration = fadeAndDropDuration + ', ' + fadeAndDropDuration;

    var leafDelay = durationValue(randomFloat(0, 5));
    leafDiv.style.webkitAnimationDelay = leafDelay + ', ' + leafDelay;

    image.style.webkitAnimationDuration = spinDuration;

    // add the <img> to the <div>
    leafDiv.appendChild(image);

    /* Return this img element so it can be added to the document */
    return leafDiv;
}


/* Calls the init function when the "Falling Leaves" page is full loaded */
window.addEventListener('load', init, false);