javascript - How can I get jquery to execute animations in exact parallel?

Question

I'm trying to create an accordion widget in jquery similar to jquery's accordion plugin, with the difference that I want the handles to appear below their respective content instead of above. My accordion works by decreasing the height of the open content section while at the same time increasing the height of the clicked content section. I've posted an example here. My problem is that the animations aren't started at exactly the same time, and there is a noticeable "jump" due to the slight delay before the second animation is started.

Scriptaculous has a function called Effect.Parallel that allows you to create an array of animation effects and execute them in parallel. Unfortunately, I can't seem to find something similar with jquery.

Is there a way I can run precise parallel animations on separate divs in jquery?

Edit: I'm as much interested in alternative methods of coding this accordion widget. So if there is any other method people think would work I'm open to that.

Answer 1

One more answer, hopefully my last one...

Unfortunately, John Resig's syncAnimate method is not quite up to snuff for the accordion-type animation I want to do. While it works great on Firefox, I couldn't get it working smoothly on IE or Safari.

With that said, I decided to bite the bullet and write my own animation engine that does simple parallel animations. The class-code uses jquery functions but is not a jquery plugin. Also, I've only set it up to do size/position animations, which is all I need.

ParallelAnimations = function(animations, opts){
    this.init(animations, opts);
};

$.extend(ParallelAnimations.prototype, {
    options: {
        duration: 250
    },
    rules: {},

    init: function(animations, opts){
        // Overwrite the default options
        $.extend(this.options, opts);

        // Create a set of rules to follow in our animation
        for(var i in animations){
            this.rules[i] = {
                element: animations[i].element,
                changes: new Array()
            };

            for(var style in animations[i].styles){

                // Calculate the start and end point values for the given style change
                var from = this.parse_style_value(animations[i].element, style, "");
                var to = this.parse_style_value(animations[i].element, style, animations[i].styles[style]);

                this.rules[i].changes.push({
                    from: from,
                    to: to,
                    style: style
                });
            }
        }

        this.start()
    },

    /*
     * Does some parsing of the given and real style values
     * Allows for pixel and percentage-based animations
     */
    parse_style_value: function(element, style, given_value){
        var real_value = element.css(style);

        if(given_value.indexOf("px") != -1){
            return {
                amount: given_value.substring(0, (given_value.length - 2)),
                unit: "px"
            };
        }

        if(real_value == "auto"){
            return {
                amount: 0,
                unit: "px"
            };
        }

        if(given_value.indexOf("%") != -1){
            var fraction = given_value.substring(0, given_value.length - 1) / 100;

            return {
                amount: (real_value.substring(0, real_value.length - 2) * fraction),
                unit: "px"
            };
        }

        if(!given_value){
            return {
                amount: real_value.substring(0, real_value.length - 2),
                unit: "px"
            };
        }
    },

    /*
     * Start the animation
     */
    start: function(){
        var self = this;
        var start_time = new Date().getTime();
        var freq = (1 / this.options.duration);

        var interval = setInterval(function(){
            var elapsed_time = new Date().getTime() - start_time;

            if(elapsed_time < self.options.duration){
                var f = elapsed_time * freq;

                for(var i in self.rules){
                    for(var j in self.rules[i].changes){
                        self.step(self.rules[i].element, self.rules[i].changes[j], f);
                    }
                }
            }
            else{
                clearInterval(interval);

                for(var i in self.rules){
                    for(var j in self.rules[i].changes)
                        self.step(self.rules[i].element, self.rules[i].changes[j], 1);
                }
            }
        }, 10);
    },

    /*
     * Perform an animation step
     * Only works with position-based animations
     */ 
    step: function(element, change, fraction){

        var new_value;
        switch(change.style){
            case 'height':
            case 'width':
            case 'top':
            case 'bottom':
            case 'left':
            case 'right':
            case 'marginTop':
            case 'marginBottom':
            case 'marginLeft':
            case 'marginRight':
                new_value = Math.round(change.from.amount - (fraction * (change.from.amount - change.to.amount))) + change.to.unit;
                break;
        }

        if(new_value)
            element.css(change.style, new_value);
    }
});

Then the original Accordion class only needs to be modified in the animate method to make use of the new call.

Accordion = function(container_id, options){
    this.init(container_id, options);
}

$.extend(Accordion.prototype, {
    container_id: '',
    options: {},
    active_tab: 0,    
    animating: false,
    button_position: 'below',
    duration: 250,
    height: 100,

    handle_class: ".handle",
    section_class: ".section",

    init: function(container_id, options){
        var self = this;
        this.container_id = container_id;
        this.button_position = this.get_button_position();

        // The height of each section, use the height specified in the stylesheet if possible
        this.height = $(this.container_id + " " + this.section_class).css("height");

        if(options && options.duration)    this.duration = options.duration;
        if(options && options.active_tab)  this.active_tab = options.active_tab;

        // Set the first section to have a height and be "open"
        // All the rest of the sections should have 0px height
        $(this.container_id).children(this.section_class).eq(this.active_tab)
            .addClass("open")
            .css("height", this.height)
            .siblings(this.section_class)
            .css("height", "0px");

        // figure out the state of the handles
        this.do_handle_logic($(this.container_id).children(this.handle_class).eq(this.active_tab));

        // Set up an event handler to animate each section
        $(this.container_id + " " + this.handle_class).mouseover(function(){

            if(self.animating)
                return;

            self.animate($(this));
        });
    },

    /*
     * Determines whether handles are above or below their associated section
     */     
    get_button_position: function(){
        return ($(this.container_id).children(":first").hasClass(this.handle_class) ? 'above' : 'below');
    },

    /*
     * Animate the accordion from one node to another
     */ 
    animate: function(handle){
        var active_section = (this.button_position == 'below' ? handle.prev() : handle.next());    
        var open_section = handle.siblings().andSelf().filter(".open");

        if(active_section.hasClass("open"))
            return;

        this.animating = true;

        // figure out the state of the handles
        this.do_handle_logic(handle);

        // Close the open section
        var arr = new Array();
        arr.push({
            element: open_section,
            styles: {
                "height": "0px"
            }
        });
        arr.push({
            element: active_section,
            styles: {
                "height": this.height
            }
        });
        new ParallelAnimations(arr, {duration: this.duration});

        var self = this;
        window.setTimeout(function(){
            open_section.removeClass("open");
            active_section.addClass("open");
            self.animating = false;
        }, this.duration);
    },

    /*
     * Update the current class or "state" of each handle
     */ 
    do_handle_logic: function(handle){
        var all_handles = handle.siblings(".handle").andSelf();
        var above_handles = handle.prevAll(this.handle_class);
        var below_handles = handle.nextAll(this.handle_class);

        // Remove all obsolete handles
        all_handles
            .removeClass("handle_on_above")
            .removeClass("handle_on_below")
            .removeClass("handle_off_below")
            .removeClass("handle_off_above");

        // Apply the "on" state to the current handle
        if(this.button_position == 'below'){
            handle
                .addClass("handle_on_below");
        }
        else{
            handle
                .addClass("handle_on_above");
        }

        // Apply the off above/below state to the rest of the handles
        above_handles
            .addClass("handle_off_above");

        below_handles
            .addClass("handle_off_below");
    }
});

The HTML is still called the same way:

<html>
<head>
    <title>Parallel Accordion Animation</title>
    <script type="text/javascript" src="jquery.js"></script>
    <script type="text/javascript" src="ui.js"></script>
    <script type="text/javascript">
    $(document).ready(function(){
        new Accordion("#accordion");
    });
    </script>
    <style type="text/css">
    #accordion{
        position: relative;
    }
    #accordion .handle{
        width: 260px;
        height: 30px;
        background-color: orange;
    }
    #accordion .section{
        width: 260px;
        height: 445px;
        background-color: #a9a9a9;
        overflow: hidden;
        position: relative;
    }
    </style>
</head>
<body>

<div id="accordion">
    <div class="section"><!-- --></div>
    <div class="handle">handle 1</div>
    <div class="section"><!-- --></div>
    <div class="handle">handle 2</div>
    <div class="section"><!-- --></div>
    <div class="handle">handle 3</div>
    <div class="section"><!-- --></div>
    <div class="handle">handle 4</div>
    <div class="section"><!-- --></div>
    <div class="handle">handle 5</div>
</div>

</body>
</html>

There are a few things I may add in the future: - Queued Animations - Animations for other types of styles (colors,etc)