JQuery 实现的页面滚动时浮动窗口控件

( function( $ ) {

    $.scrollFollow = function ( box, options )
    {
        // Convert box into a jQuery object
        box = $( box );

        // 'box' is the object to be animated
        var position = box.css( 'position' );

        function ani()
        {        
            // The script runs on every scroll which really means many times during a scroll.
            // We don't want multiple slides to queue up.
            box.queue( [ ] );

            // A bunch of values we need to determine where to animate to
            var viewportHeight = parseInt( $( window ).height() );    
            var pageScroll = parseInt( $( document ).scrollTop() );
            var parentTop = parseInt( box.cont.offset().top );
            var parentHeight = parseInt( box.cont.attr( 'offsetHeight' ) );
            var boxHeight = parseInt( box.attr( 'offsetHeight' ) + ( parseInt( box.css( 'marginTop' ) ) || 0 ) + ( parseInt( box.css( 'marginBottom' ) ) || 0 ) );
            var aniTop;

            // Make sure the user wants the animation to happen
            if ( isActive )
            {
                // If the box should animate relative to the top of the window
                if ( options.relativeTo == 'top' )
                {
                    // Don't animate until the top of the window is close enough to the top of the box
                    if ( box.initialOffsetTop >= ( pageScroll + options.offset ) )
                    {
                        aniTop = box.initialTop;
                    }
                    else
                    {
                        aniTop = Math.min( ( Math.max( ( -parentTop ), ( pageScroll - box.initialOffsetTop + box.initialTop ) ) + options.offset ), ( parentHeight - boxHeight - box.paddingAdjustment ) );
                    }
                }
                // If the box should animate relative to the bottom of the window
                else if ( options.relativeTo == 'bottom' )
                {
                    // Don't animate until the bottom of the window is close enough to the bottom of the box
                    if ( ( box.initialOffsetTop + boxHeight ) >= ( pageScroll + options.offset + viewportHeight ) )
                    {
                        aniTop = box.initialTop;
                    }
                    else
                    {
                        aniTop = Math.min( ( pageScroll + viewportHeight - boxHeight - options.offset ), ( parentHeight - boxHeight ) );
                    }
                }

                // Checks to see if the relevant scroll was the last one
                // "-20" is to account for inaccuracy in the timeout
                if ( ( new Date().getTime() - box.lastScroll ) >= ( options.delay - 20 ) )
                {
                    box.animate(
                        {
                            top: aniTop
                        }, options.speed, options.easing
                    );
                }
            }
        };

        // For user-initiated stopping of the slide
        var isActive = true;

        if ( $.cookie != undefined )
        {
            if( $.cookie( 'scrollFollowSetting' + box.attr( 'id' ) ) == 'false' )
            {
                var isActive = false;

                $( '#' + options.killSwitch ).text( options.offText )
                    .toggle(
                        function ()
                        {
                            isActive = true;

                            $( this ).text( options.onText );

                            $.cookie( 'scrollFollowSetting' + box.attr( 'id' ), true, { expires: 365, path: '/'} );

                            ani();
                        },
                        function ()
                        {
                            isActive = false;

                            $( this ).text( options.offText );

                            box.animate(
                                {
                                    top: box.initialTop
                                }, options.speed, options.easing
                            );    

                            $.cookie( 'scrollFollowSetting' + box.attr( 'id' ), false, { expires: 365, path: '/'} );
                        }
                    );
            }
            else
            {
                $( '#' + options.killSwitch ).text( options.onText )
                    .toggle(
                        function ()
                        {
                            isActive = false;

                            $( this ).text( options.offText );

                            box.animate(
                                {
                                    top: box.initialTop
                                }, 0
                            );    

                            $.cookie( 'scrollFollowSetting' + box.attr( 'id' ), false, { expires: 365, path: '/'} );
                        },
                        function ()
                        {
                            isActive = true;

                            $( this ).text( options.onText );

                            $.cookie( 'scrollFollowSetting' + box.attr( 'id' ), true, { expires: 365, path: '/'} );

                            ani();
                        }
                    );
            }
        }

        // If no parent ID was specified, and the immediate parent does not have an ID
        // options.container will be undefined. So we need to figure out the parent element.
        if ( options.container == '')
        {
            box.cont = box.parent();
        }
        else
        {
            box.cont = $( '#' + options.container );
        }

        // Finds the default positioning of the box.
        box.initialOffsetTop = parseInt( box.offset().top );
        box.initialTop = parseInt( box.css( 'top' ) ) || 0;

        // Hack to fix different treatment of boxes positioned 'absolute' and 'relative'
        if ( box.css( 'position' ) == 'relative' )
        {
            box.paddingAdjustment = parseInt( box.cont.css( 'paddingTop' ) ) + parseInt( box.cont.css( 'paddingBottom' ) );
        }
        else
        {
            box.paddingAdjustment = 0;
        }

        // Animate the box when the page is scrolled
        $( window ).scroll( function ()
            {
                // Sets up the delay of the animation
                $.fn.scrollFollow.interval = setTimeout( function(){ ani();} , options.delay );

                // To check against right before setting the animation
                box.lastScroll = new Date().getTime();
            }
        );

        // Animate the box when the page is resized
        $( window ).resize( function ()
            {
                // Sets up the delay of the animation
                $.fn.scrollFollow.interval = setTimeout( function(){ ani();} , options.delay );

                // To check against right before setting the animation
                box.lastScroll = new Date().getTime();
            }
        );
        // Run an initial animation on page load
        box.lastScroll = 0;

        ani();
    };

    $.fn.scrollFollow = function ( options )
    {
        options = options || {};
        options.relativeTo = options.relativeTo || 'top';
        options.speed = options.speed || 1;
        options.offset = options.offset || 0;
        options.easing = options.easing || 'swing';
        options.container = options.container || this.parent().attr( 'id' );
        options.killSwitch = options.killSwitch || 'killSwitch';
        options.onText = options.onText || 'Turn Slide Off';
        options.offText = options.offText || 'Turn Slide On';
        options.delay = options.delay || 0;

        this.each( function()
            {
                new $.scrollFollow( this, options );
            }
        );

        return this;
    };
})( jQuery );

<script type="text/javascript"><!--
$( document ).ready( function ()
{
$( '#example' ).scrollFollow();
}
);
// --></script>

#example {
position: relative;
width: 220px;
margin: 5px;
padding: 10px;
background: #DDDDDD;
border: 1px solid #42CBDC;
}