Plugins – Page 3 – computeraxe

Slideshow Loading Problems Solved in jQuery Cycle

When it comes to JavaScript components that act on elements of the page, it is highly important to have those elements in place before the script tries to manipulate them, else things won’t work as intended. So, that begs the question, “What’s the best way to have JavaScript run on my page?” In this example we’ll focus on handling javascript while making slideshows with the jQuery Cycle plugin.

At any rate we want our pages to be seen by the visitor right away. We know if it takes more than a couple of seconds for anything to appear on the screen, the visitor is likely to click away to another site. Remember, text appears quickly when it’s not part of a table. The whole table has to be ready before you’ll see the table, so don’t use tables for design purposes, especially nested tables. Save your tables for presenting data.

A problem with big pages having slideshows is that if the page is not ready when a script tries to manipulate things, the effects may be all wrong. For example, when a script calculates the center position for an image it may get the positioning wrong, especially if all the images in the slideshow are not of the same size.

So, how do we improve our slideshow for the masses? We need to tell the javascript when to do its magic. In this example we’ll use this approach:

Perform initial actions with the .ready() method. Actions in this case are to hide images with the .hide() method until they are called for by the script.
Run the slideshow after the content has loaded with the .load() method.
Use a function to calculate the center for each image.
Apply the function with the before option in jQuery Cycle.

A previous post on centering slideshows with jQuery Cycle put all the javascript inside a .ready() statement. For many scripts this would be just fine, but for the slideshow it resulted in the action starting up before all the images were available.

For this example the slideshow is marked up as a group of images inside a <div> that has been assigned an id for JS targeting, #big_show, and a class for CSS targeting, .photos.

HTML Markup:

[plain]

[/plain]

Hide Images While Page Loads

Because it may take a while to load up all the photos for the slideshow, and everything else on the page, hide the photos except for the first one to start. Use a .ready() statement to hide the photos because we want to do that right away. Put everything in the .ready() method that you want to run first, even before the rest of the page or content has loaded. The .ready() function is a jQuery construct that allows you to bring functionality to the page before all the content has loaded. That way a page with lot of images can be useful even before all the images are visible.

For hiding images use the .ready() function so that this task will occur as soon as possible.

[crayon]
$(document).ready(function() {
$(‘#s1 img:gt(0)’).hide(); // hides all images with index greater than 0, so it shows the first image only – in one JS/jQuery call

$(‘#s2 img’).hide(); // hides all images
$(‘#s2 img:first’).show(); // shows the first image

$(‘#s3 img’).hide(); // hides all images
$(‘#s3 img:eq(0)’).show(); // shows the image with index equal to 0
});
[/crayon]

Many selectors could be used to target the first element in a series and the example above shows three ways of doing so for three different slideshows, #s1, #s2 and #s3. The outcome of each is the same in that only the first image is shown until the rest of the slideshow is loaded.

Control Slideshow Action After Window Loads

It makes sense to run a slideshow only when all the components for the show are present. To do that run Cycle with a .load() statement so that the slideshow waits to start until all of the images are loaded.

[crayon]
$(window).load(function() {
$(‘#big_show’).cycle({
fx: ‘fadeZoom’,
timeout: 2000,
before: onBefore
});
});
[/crayon]

If you have a big slide show with lots of images, you might want to present an animated loading image until the slideshow starts.

Calculate Image Size for Centering in Slideshow

Take a look at the solution provided by “malsup” for users of his Cycle plugin:

[crayon]
function onBefore(curr,next,opts) {
var $slide = $(next);
var w = $slide.outerWidth();
var h = $slide.outerHeight();
$slide.css({
marginTop: (400 – h) / 2,
marginLeft: (300 – w) / 2
});
};
[/crayon]

Basically, what his code is doing is creating a function that will run before any slides are manipulated by Cycle. The purpose of the onBefore function is to calculate the correct margins for images and set the CSS parameters margin-top and margin-left for centering the images.

The onBefore function creates a variable called $slide to hold an array of the parameters of the $(next) element in the slideshow. The variables w and h are set to the width and height of said element via the $slide.outerWidth() and $slide.outerHeight() methods, respectively.

Finally, the margins are calculated from knowing the width and height of the slide container as set in the CSS (in this example 400 px and 300 px) and subtracting the slide’s width (w) and height (h) values, respectively. The margins only need to have half of the total margin value to accommodate both sides of the box, so the difference is divided by 2.

Use Cycle’s Before Option to Apply Centering Function

Using the onBefore function with Cycle’s before option works beautifully with images of different sizes, see line 5 of the .load() method above. Margins are set using the .css() method after they are calculated by the onBefore function.

CSS:

[plain]
#big_show {
height: 400px;
width: 300px;
text-align: center;
background-color: #f3c;
}
.photos img {
margin: 0;
padding: 4px;
border: 1px solid #ccc;
background-color: #eee;
max-width: 290px;
max-height: 390px;
}
[/plain]

You have to specify some CSS to get this thing to work right, namely set the width and height on the slide container and slides themselves.

Setting the max-width and max-height for the images helps to keep them inside of the container. Note that adding up the padding and border for both sides of the box is 10 px of the slideshow box that can’t be used to show an image. Therefore, the maximum image dimensions are the overall width or height minus 10 px. By accounting for the padding and border sizes a large image won’t overflow its container.

Any comments on this improved slideshow using Cycle plugin with jQuery?

Slideshow Image Captions with jQuery Cycle

If a picture is worth a thousand words, a photo slideshow would be worth a whole book. Images can be interpreted in many ways and without some accompanying text or captions for the images in a slide show, you force the visitor to draw their own conclusions about what they are viewing. In the art world this may be ok and perhaps what you’re striving for, but most of the time we want to provide additional information with images so the visitor really knows what the imagery is all about.

Some images are fairly meaningless without captions. Were those pictures taken before or after the event? And is that really Aunt Tillie as a hip youngster?! You get the idea…captions help us to tell our stories. They can be as short and sweet as you like or more explanatory in nature. It just depends on your purpose as to what kinds of captions your visitors would benefit from.

Presented here are three examples for producing image captions in slideshows with jQuery Cycle.

To make an image caption for jQuery Cycle slideshows, the examples that follow depend on passing selectors, like this.alt, to the .html() method to pick up the alt text from each <img>. Also, we’re going to use Cycle’s after and before options to specify our image captions.

Example 1: Use Cycle’s after option to specify a caption using the image’s alt text. Caption will appear after the slide is in place.

[crayon]
$(‘#slide_after’).cycle({
fx: ‘shuffle’,
timeout: 2000,
slideExpr: ‘img’,
after: function() {
$(‘#caption’).html(this.alt);
}
});
[/crayon]

Here, the after option takes the result of an anonymous function as its value. The function() inserts the alt text from this, the current image, into #caption. In the HTML markup below notice that #caption identifies a paragraph below the images.

Example 1 HTML Markup:

[plain]

[/plain]

Example 1 Slideshow:

Example 2: Use Cycle’s before option to specify a caption using the image’s alt text. Caption will appear before the next slide.

[crayon]
$(‘#slide_before’).cycle({
fx: ‘shuffle’,
timeout: 2000,
slideExpr: ‘img’,
before: function() {
$(‘#caption2’).html(this.alt);
}
});
[/crayon]

The only things changed from Example 1 are that we’re using Cycle’s before option instead of the after option and the captions are placed at the top of the images instead of below them.

Example 2 HTML Markup:

[plain]

[/plain]

Example 2 Slideshow:

Example 3: Show slide number and total count of slides in addition to the image’s alt text for a caption.

To get the slide numbers we can take advantage of a couple of variables that keep track of the current slide and the number of total slides. We’ll pass three Cycle variables (curr,next,opts) to a new function.

[crayon]
$(‘#slideboth’).cycle({
fx: ‘fadeZoom’,
timeout: 2000,
slideExpr: ‘img’,
after: slideAfter,
before: function() {
$(‘#caption3’).html(this.alt);
}
});

function slideAfter(curr,next,opts) {
var caption_count = ‘Image ‘ + (opts.currSlide + 1) + ‘ of ‘ + opts.slideCount;
$(‘#caption4’).html(caption_count);
}
[/crayon]

There’s something new going on here. A named function, slideAfter, is the value for the after option. Using a function we can make calculations and assignments to create some interesting captions. Cycle’s before option also may take a function as its value.

The function slideAfter calculates and specifies the number of the current image and the total number of slides in the slideshow. The calculated values are assigned to a variable, caption_count, which is then used as the image caption.

Example 3 HTML Markup:

[plain]

()

[/plain]

In this example #caption5 is used for CSS positioning, while #caption3 and #caption4 are targeted by the JavaScript in creating the caption.

Example 3 Slideshow:

()

Examples borrowed from jQuery Cycle image count caption demo.

These examples showed how to create captions for images presented in slideshows with the jQuery Cycle plugin.

Specify Children for jQuery Cycle Slideshows

The jQuery Cycle plugin is a versatile JavaScript plugin for making slideshows.

The default behavior is to fade in a new slide, let the viewer see the slide for four seconds, then fade out that slide as the next one fades in. Slides are faded in and out continuously and in a sequential manner. Unless specified in the options, a slideshow starts with the first slide and cycles through all slides, then loops back to the first slide, running continuously.

Options are available to change every aspect of the slideshow behavior, so the kind and timing of the transitions can be easily changed, as well as the starting and ending slides of the show.

It’s beyond the scope of this post to review all the Cycle options, but one option that may come in handy is the slideExpr option. The default value is ‘NULL‘ and it’s described as the “expression for selecting slides (if something other than all children is required)”.

So far, there are two instances where slideExpr has saved my day. Basically, it lets you specify the children of the slideshow and that’s important if you’re using WordPress or if you’re wrapping slides in links.

WordPress or Other CMS

Using JavaScript inside WordPress posts can be tricky. One has to properly register and queue up the scripts with the methods wp_register_script() and wp_enqueue_script() instead of inserting <script> tags in the page headers.

Still, things may not look right when a post is previewed because of the way that WordPress assembles the pages we see on the World Wide Web. WordPress or another content management system (CMS) may insert line breaks that interrupt the flow of a slideshow.

Remember, with the Cycle plugin every child element inside the slideshow container will become a slide. That means every CMS inserted <br /> will be treated as a slide. This produces a slideshow with long, blank pauses in between the actual slides, like the slideshow on the left below, #show_a.

Use slideExpr to specify the children elements for slideshows in WordPress. This avoids extraneous elements from the content management system from being interpreted as slides. See the slideshow on the right below, #show_b.

HTML Markup:

[plain]

[/plain]

The left slideshow, #show_a, shows a few different transitions without using slideExpr, which gives a background-colored pause or blank pause in between each slide. This slideshow assumes the first-level children are the elements to be manipulated in the slideshow.

The right slideshow, #show_b, shows the same transitions with slideExpr set to ‘img’. This gives the expected behavior where only the images, <img>, are treated as slides, not any other element that may be inserted by WordPress or by the developer.

JavaScript:

[crayon]
$(‘#show_a’).cycle({
fx: ‘fade,toss,fadeZoom’,
speed: 700,
timeout: 2000
});

$(‘#show_b’).cycle({
fx: ‘fade,toss,fadeZoom’,
speed: 700,
timeout: 2000,
slideExpr: ‘img’
});
[/crayon]

Wrapping slides

If you’re not using WordPress or another CMS, there may still be unexpected behavior with the Cycle plugin with respect to children of the slide show.

Any children in a container element can be used as a slide with the jQuery Cycle plugin. Designers can get as fancy or as funky as they want to with their slideshows because they ultimately have complete control. If you want to wrap each image in an anchor which is wrapped in a styling div, that’s ok.

Just remember to use slideExpr: ‘img’ if it is the images that you want to transition from slide to slide. HTML Markup is very similar to that above with different container ids for JavaScript and CSS targeting.

In this example the slideshow on the left, #show_1, uses the ‘fadeZoom’ transition effect without slideExpr. Slideshow #show_2 on the right uses the ‘fadeZoom’ transition effect with slideExpr: ‘img’. Note how the actual transition effect is different depending on which element is serving as the slide.

JavaScript:

[crayon]
$(‘#show_1’).cycle({
fx: ‘fadeZoom’,
speedIn: 700,
speedOut: 1200,
timeout: 2000
});

$(‘#show_2’).cycle({
fx: ‘fadeZoom’,
speedIn: 700,
speedOut: 1200,
timeout: 2000,
slideExpr: ‘img’
});
[/crayon]

Note the empty paragraph in the HTML markup for each slideshow. Without specifying the slideExpr option, as in #show_1, the empty paragraph is treated as a slide and a blank space is shown for it. Slideshow #show_2 specifies that the images are to be the sliding elements, so no blank space is seen.

Certain transition effects problems may appear when wrapping slides with links in jQuery Cycle. Using the slideExpr option is an easy solution.

jQuery Cycle Plugin Working with Links

The Cycle plugin for use with the jQuery library can be described as a robust, mature and versatile JavaScript plugin. Plentiful options allow every aspect of a slideshow created with Cycle to be modified.

For interactive slideshows where you’d like the user to be able to click on a slide to get more information, wrap an anchor around each slide. Then, when the user clicks on a slide they will be shown the target link. You could show the user a larger image, an expanded view of a portion of the image, or more descriptive text about the slide.

The markup is straightforward, using an unordered list of links:

[plain]

[/plain]

Transition Effects Problem

Wrapping anchors around each slide makes them clickable, but that introduces a potential problem when using the Cycle plugin. Some of the transition effects just won’t work as expected. In this example the children that will be manipulated inside the #show container are the anchor links, not the images. Even though we know it’s supposed to be the images that are to be swapped in and out of this slideshow, technically, the children that will be swapped are the anchors, and that makes a difference in how things will look. Images are contained inside the anchors, so the images won’t be manipulated, just the anchors.

Most of the available transition effects modify the size of the slide’s width and/or height to achieve the desired effect. When an anchor is wrapped around an image, the anchor’s size can be manipulated, but the contained image won’t be resized. If one of the transitions that manipulate the slide width or height has been called, the effect won’t be seen as intended.

For example, the two slideshows below use the same HTML markup, except for having different container ids, which are targeted by the script and the CSS. Images are wrapped by <a> in both the left and right slideshows below.

Here’s the HTML Markup for the example slideshows below:

[plain]

[/plain]

Using one of the turn effects illustrates how the different children behave. The slideshow on the left is manipulating anchors, while a slight change in the script allows the slideshow on the right to manipulate the images. Both slideshows below use the turnDown transition effect.

Watch each slide transition and you’ll see that the one on the left doesn’t show any turning behavior as the top slide is dragged off the lower slide. In the slideshow on the right the turnDown effect can be seen as the images are manipulated in a way to make it look like the next image is being turned down from above.

This phenomenon happens using the jQuery Cycle plugin when an anchor, <div>, or any other tag wraps around the images, in effect taking their place as children of the slideshow container.

slideExpr Solution

One solution is to use the slideExpr option. The default value for slideExpr is ‘NULL‘ which indicates that the default children will be manipulated as the slides, as in the slideshow on the left.

[crayon]
$(‘#showleft’).cycle({
fx: ‘turnDown’,
speed: 700,
timeout: 2000
});

$(‘#showright’).cycle({
fx: ‘turnDown’,
speed: 700,
timeout: 2000,
slideExpr: ‘img’
});
[/crayon]

The slideshow on the right, #showright, has specified the option slideExpr: ‘img’ to assure that the <img> should be treated as slides, see line 11. By specifying which element should be treated as the children of the slideshow container, the transition fx can be seen as intended.

Slideshows can use any content for slides, so remember that extra elements in the slideshow container will be treated as slides. Inspect the HTML markup above and take note of the blank paragraph in each slideshow container. The default slideshow on the left, #showleft, assumes that the <p> is a child that is part of the slideshow, so it shows a blank paragraph after the last slide. Only images are slides in the slideshow #showright, so its behavior is to wrap around to the first <img>, instead of showing the blank paragraph as the last slide.

fx Solution

Another way to avoid the transition effect problem is to stick with the slide transitions that aren’t affected when using wrappers around slides. When the design requires wrapping slides in anchors or divs, pick from the subset of transition effects that doesn’t modify the image size. To see the true effects use fade, scrollUp, scrollDown, scrollLeft, scrollRight, and shuffle for slide transitions.

Note: The blank spaces between each slide in #showleft are due to the way that WordPress assembles a webpage or post. Use slideExpr with WordPress to avoid having WordPress-injected elements acting as slides in slideshows with the jQuery Cycle plugin.