/*

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: Dropper.js

Abstract: Defines JavaScript functionality for the Leaves sample.

          Creates a JavaScript object that contains all required 

          information to animate the leaves.

Version: 1.0

Disclaimer: IMPORTANT:  This Apple software is supplied to you by

Apple Inc. ("Apple") in consideration of your agreement to the

following terms, and your use, installation, modification or

redistribution of this Apple software constitutes acceptance of these

terms.  If you do not agree with these terms, please do not use,

install, modify or redistribute this Apple software.

In consideration of your agreement to abide by the following terms, and

subject to these terms, Apple grants you a personal, non-exclusive

license, under Apple's copyrights in this original Apple software (the

"Apple Software"), to use, reproduce, modify and redistribute the Apple

Software, with or without modifications, in source and/or binary forms;

provided that if you redistribute the Apple Software in its entirety and

without modifications, you must retain this notice and the following

text and disclaimers in all such redistributions of the Apple Software.

Neither the name, trademarks, service marks or logos of Apple Inc.

may be used to endorse or promote products derived from the Apple

Software without specific prior written permission from Apple.  Except

as expressly stated in this notice, no other rights or licenses, express

or implied, are granted by Apple herein, including but not limited to

any patent rights that may be infringed by your derivative works or by

other works in which the Apple Software may be incorporated.

The Apple Software is provided by Apple on an "AS IS" basis.  APPLE

MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION

THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS

FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND

OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.

IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL

OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,

MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED

AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),

STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE

POSSIBILITY OF SUCH DAMAGE.

Copyright (C) 2008 Apple Inc. All Rights Reserved.

*/

/*

    Creates a JavaScript object that implements fade and drop animations on the y-axis.

    Takes four parameters: element, startPosition, endPosition, and duration. 

    The element parameter refers to the html element to be animated, startPosition

    and endPosition respectively determine where to start and end the animations on the the y-axis,

    and duration specifies the length of the animation.

*/

function Dropper(element, startPosition, endPosition, duration)

{

    /* Track all parameters of the Dropper instance object */

    this.element = element;

    this.startPositionOnYAxis = startPosition;

    this.endPositionOnYAxis = endPosition;

    this.duration = duration;

    /* timeout will be used to start and stop the animation */

    this.timeout = null;

};

/*

    Updates both startTime and endTime variables that respectively specify the times at 

    which the animations will start and end. Calls the loop function to start the animations.

*/

Dropper.prototype.start = function ()

{

    /* Do nothing if the values of startPositionOnYAxis and endPositionOnYAxis are identical */

    if (this.startPositionOnYAxis == this.endPositionOnYAxis) 

    {

        return;

    }

    /* Track the animation time, get its starting time here */

    this.startTime = new Date();

    /* Get the current duration in milliseconds, add it to the above starting time, and assign it to the endTime variable */

    this.endTime = this.startTime.getTime() + (this.duration * 1000);

    /* Calls the loop function to start the animation */

    this.loop();

};

/* 

    Performs the animations. Check the elapsed time for the current animation.

    Moves the element to its final position, stops the current animation,

    and restarts the animation process if that time is equal to or greater than

    the current time. 

    Updates the top and opacity properties of the elements if we are still within

    the allocated time for the animation. 

*/

Dropper.prototype.loop = function ()

{

    /* Get the current time */

    var now = new Date();

    /* Check whether we have reached or gone past the end time */

    if (now >= this.endTime) 

    {

        /* If so, set the final position */

        this.setTopAttribute(this.endPositionOnYAxis);

        /* Clear current animation */

        window.clearTimeout(this.timeout);

        /* Restart the animation */

        this.start();

        return;

    }

    /* Otherwise, figure out how far along we are within the animation */

    var offset = (now - this.startTime) / (this.duration * 1000);

    /* Compute and set the current height based on offset */

    this.setTopAttribute(this.startPositionOnYAxis + (offset * (this.endPositionOnYAxis - this.startPositionOnYAxis)));

    /*And if we are real close to the end of the animation, update the opacity for a gradual fade out */

    this.setOpacity( (offset > 0.95) ? 1.0 - (offset - 0.95) * 20.0 : 1.0 );

    /* Finally, call the loop function again in 10 ms */

    var _this = this;

    this.timeout = window.setTimeout(function () { _this.loop() }, 10);

};

/*

    Updates the top position of an element.  

*/

Dropper.prototype.setTopAttribute = function (newTopPosition)

{

    this.element.style.top = pixelValue(newTopPosition);

};

/*

    Updates an element's opacity.

*/

Dropper.prototype.setOpacity = function (newOpacity)

{

    this.element.style.opacity = newOpacity;

};