Backstretch

Backstretch is a simple jQuery plugin that allows you to add a dynamically-resized, slideshow-capable background image to any page or element. The image will stretch to fit the page/element, and will automatically resize as the window/element size changes.

Original Repository

Is here: https://github.com/srobbin/jquery-backstretch
But we haven't seen any kind of activity by the author for about 2 years already. So I've taken the PRs that were there and merged them carefully, with some improvements and cleanup. This fork is the result.

Demo

There are a couple of examples included with this package, or feel free to check it out live on the project page itself.

Setup

Include the jQuery library (version 1.7 or newer) and Backstretch plugin files in your webpage (preferably at the bottom of the page, before the closing BODY tag):

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script src="jquery.backstretch.min.js"></script>
<script>
  // To attach Backstrech as the body's background
  $.backstretch("path/to/image.jpg");

  // You may also attach Backstretch to a block-level element
  $(".foo").backstretch("path/to/image.jpg");

  // If your element defines a background image with CSS, you can omit the argement altogether
  $(".foo").backstretch();

  // Or, to start a slideshow, just pass in an array of images
  $(".foo").backstretch([
    "path/to/image.jpg",
    "path/to/image2.jpg",
    "path/to/image3.jpg"    
  ], {duration: 4000});

  // Or, to load from a url that can accept a resolution and provide the best image for that resolution
  $(".foo").backstretch([
    "path/to/image.jpg?max_width={width}&max_height={height}"
  ]);

  // Or, to automatically choose from a set of resolutions
  // (Each width specifies the minimum resolution for specific image)
  $(".foo").backstretch([
    [
      width: 720, url: "path/to/image1_1080.jpg",
      width: 320, url: "path/to/image1_720.jpg",
      width: 0, url: "path/to/image1_320.jpg"
    ],
    [
      width: 720, url: "path/to/image2_1080.jpg",
      width: 320, url: "path/to/image2_720.jpg",
      width: 0, url: "path/to/image2_320.jpg"
    ]
  ]);
</script>

Options

Name	Description	Type	Default
centeredX	The ratio of the width/height of the image doesn't always jive with the width/height of the window. This parameter controls whether or not we center the image on the X axis to account for the discrepancy.	Boolean	true
centeredY	This parameter controls whether or not we center the image on the Y axis to account for the aforementioned discrepancy.	Boolean	true
alignX	This parameter controls the horizontal alignment of the image. Can be one of: "auto", "center", "left", "right". If different from "auto", it takes prcedence over the value of centeredX.	String	"auto"
alignY	This parameter controls the vertical alignment of the image. Can be one of: "auto", "center", "top", "bottom". If different from "auto", it takes prcedence over the value of centeredY.	String	"auto"
fade	This is the speed at which the image will fade in. Integers in milliseconds are accepted, as well as standard jQuery speed strings (slow, normal, fast).	Integer or String	0
fadeFirst	If true, the first image will fade in like all the others.	Boolean	true
duration	The amount of time in between slides, when using Backstretch as a slideshow, expressed as the number of milliseconds.	Integer	5000
paused	For slideshows: Disables the change between slides	Boolean	false
start	The index of the image in the array you want to start your slideshow with.	Integer	0
preload	How many images to preload at once? I.e. Lazy-loading can be enabled by specifying 0.	Integer	2
preloadSize	How many images to preload in parallel? If we are preloading 5 images for the next slides, we might want to still limit it to only preload 2 or 3 at once, according to the expected available bandwidth.	Integer	1

Slideshow API

Once you've instantiated a Backstretch slideshow, there are many actions that you can perform it:

// Start a slideshow
$('.foo').backstretch([
  'path/to/image.jpg',
  'path/to/image2.jpg',
  'path/to/image3.jpg'
]);

// Pause the slideshow
$('.foo').backstretch("pause");

// Advance to the next slide
$('.foo').backstretch("next");

Method	Description
.backstretch("show", n)	Jump to the slide at a given index, where n is the number of the image that you'd like to display. Slide number starts at 0.
.backstretch("prev")	Display the previous image in a slideshow.
.backstretch("next")	Advance to the next image in a slideshow.
.backstretch("pause")	Pause the slideshow.
.backstretch("resume")	Resume a paused slideshow.
.backstretch("destroy", preserveBackground)	Destroy the Backstretch instance. Optionally, you can pass in a Boolean parameter, preserveBackground, to determine whether or not you'd like to keep the current image stretched as the background image.
.backstretch("resize")	This method is called automatically when the container (window or block-level element) is resized, however you can always call this manually if needed.
.backstretch("gravity", g)	Set the alignment (NorthWest, North, NorthEast, West, Center, East, SouthWest, South, SouthEast) for the next image.

Public Variables

Sometimes, you'll want to access Backstretch's images after you've instantiated the plugin. For example, perhaps you'd like to be able add more images to a slideshow. Doing so is easy. You can access the images array as follows:

$('.foo').backstretch([
  'path/to/image.jpg',
  'path/to/image2.jpg',
  'path/to/image3.jpg'
]);

// Access the instance
var instance = $('.foo').data('backstretch');

// Then, you can manipulate the images array directly
instance.images.push('path/to/image4.jpg')

Additionally, the current index of a slideshow is available through the instance as well:

$("body").data("backstretch").index;

Events

backstretch.before

Backstretch will fire a "backstretch.before" event before a new image loads, triggering a function that is passed the event, Backstretch instance, and index of the image that will be displayed. If you listen for that event, you can, for example, coordinate other changes to coincide with your slideshow.

$(window).on("backstretch.before", function (e, instance, index) {
  // If we wanted to stop the slideshow after it reached the end
  if (index === instance.images.length - 1) {
    instance.pause();
  };
});

backstretch.after

Backstretch will also fire a "backstretch.after" event after the new images has completed loading.

$(window).on("backstretch.after", function (e, instance, index) {
  // Do something
});

Changelog

Version 2.0.6

• Minor bug fixes due to latest PRs

Version 2.0.5

• New fadeFirst feature
• New alignX feature
• New alignY feature
• New paused feature
• New start feature
• New preload feature
• New preloadSize feature
• New feature: url templates
• New feature: automatic resolution selection
• Minor bug fixes

Version 2.0

• Now accepts an array of images to create a slideshow
• Can attach Backstretch to any block-level element, not just the body
• Deprecated "speed" option in favor of "fade" for fadeIn timing
• Added "duration" option, and Slideshow API

Version 1.2

• You can now called backstretch twice, and it will replace the existing image.

Version 1.1

• Added 'centeredX' and 'centeredY' options.
• Removed 'hideUntilReady' option. It looks pretty bad if you don't hide the image until it's fully loaded.
• Fixed IE img onload bug.
• Now supports iPhone/iPad orientation changes.