Note: This repo is currently looking for maintainers: #464

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.

** We're back in business! Merged danielgindi/jquery-backstretch, and all eyes please get back here! **

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

1. Download/save the JS file from GitHub.
2. Install via Bower with the following command.

bower install jquery-backstretch

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?width={width}&height={height}"
  ]);

  // Or, to automatically choose from a set of resolutions.
  // The width is the width of the image, and the algorithm chooses the best fit.
  $(".foo").backstretch([
    [
      { width: 1080, url: "path/to/image1_1080.jpg" },
      { width: 720, url: "path/to/image1_720.jpg" },
      { width: 320, url: "path/to/image1_320.jpg" }
    ],
    [
      { width: 1080, url: "path/to/image2_1080.jpg" },
      { width: 720, url: "path/to/image2_720.jpg" },
      { width: 320, url: "path/to/image2_320.jpg" }
    ]
  ]);

  // If we wanted to specify different images for different pixel-ratios:
  $(".foo").backstretch([
    [
      // Will only be chosed for a @2x device
      { width: 1080, url: "path/to/[email protected]", pixelRatio: 2 },
      
      // Will only be chosed for a @1x device
      { width: 1080, url: "path/to/image1_1080.jpg", pixelRatio: 1 },
      
      { width: 720, url: "path/to/[email protected]", pixelRatio: 2 },
      { width: 720, url: "path/to/image1_720.jpg", pixelRatio: 1 },
      { width: 320, url: "path/to/[email protected]",  pixelRatio: 2 },
      { width: 320, url: "path/to/image1_320.jpg", pixelRatio: 1 }
    ]
  ]);

  // If we wanted the browser to automatically choose from a set of resolutions,
  // While considering the pixel-ratio of the device
  $(".foo").backstretch([
    [
      // Will be chosen for a 2160 device or a 1080*2 device
      { width: 2160, url: "path/to/image1_2160.jpg", pixelRatio: "auto" }, 
      
      // Will be chosen for a 1080 device or a 540*2 device
      { width: 1080, url: "path/to/image1_1080.jpg", pixelRatio: "auto" },
      
      // Will be chosen for a 1440 device or a 720*2 device
      { width: 1440, url: "path/to/image1_1440.jpg", pixelRatio: "auto" },
      { width: 720, url: "path/to/image1_720.jpg", pixelRatio: "auto" },
      { width: 640, url: "path/to/image1_640.jpg", pixelRatio: "auto" },
      { width: 320, url: "path/to/image1_320.jpg", pixelRatio: "auto" }
    ]
  ]);
</script>

The automatic resolution selection algorithm has multiple options to choose from.
The default behaviour is that it matches the logical width of the element against the specified image sizes. Which means that an element with a 320px width on a @2x device is still considered as 320px.
If you want 320px on a @2x device to be considered as 640px, then you can specify pixelRatio: "auto" on the specific image resolution.
However if you want to limit specific images to only be chosen if the device has a certain pixel ratio - you can specify that pixel ratio i.e pixelRatio: 2.5.

• Options marked with an * can be specified for individual images

Each image in the set can be a String specifying the URL for the image, or an object with the following options, or an array of images for different resolutions to choose between. A url can be a url to a video also. Currently the plugin will automatically recognize a youtube url. If you pass urls to raw videos, you have to specify isVideo: true.

If you have specified an array of resolutions for a single image, then these are the available options:

• 'fade'
• 'fade_in_out' / 'fadeInOut'
• 'push_left' / 'pushLeft'
• 'push_right' / 'pushRight'
• 'push_up' / 'pushUp'
• 'push_down' / 'pushDown'
• 'cover_left' / 'coverLeft'
• 'cover_right' / 'coverRight'
• 'cover_up' / 'coverUp'
• 'cover_down' / 'coverDown'

• If the video is not in loop mode, then it will play until the end. You have to specify a duration for the specific video in order to limit its playing duration.
• Mobile browsers do not allow playback of videos without the users tapping a play button... So you may want to detect those and supply different media arrays for those browsers.

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'
]);

// Slideshow with granular control
$('.foo').backstretch([
  { url: 'path/to/image.jpg', duration: 3000 }
  { url: 'path/to/image2.jpg', fade: 250 },
  { url: 'path/to/image3.jpg', alignY: 0.2 }
]);

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

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

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;

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

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

• Bugfix: When another library imports youtube api first, YT detection misbehaves in backstretch.

• Bugfix: Calling .backstretch(...) on an already backstretched element did not properly destroy the older backstretch instance. Resulted in ghost backstretches...

• New: Added scale feature.

• Improvement: Not modifying background property, but background-image, to allow CSS to play with colors. (@philsbury)

• New: Added 'deviceOrientation', 'windowOrientation' and 'orientation' options

• Bugfix: Native video source tags were misspelled
• Bugfix: Youtube matching regex was not constrained to youtube.com/youtu.be domain

• New: Added 'fade_in_out' transition

• Bugfix: Resolution detection routine failed to properly match current url - and cause an additional replace of the image. This affected video urls in a way that caused them to being played from the start.

• Bugfix: pixelRatio == 'auto' was ignored due to a missing rule.

• Allow overriding transition options for a single show(...) call
• Bugfix: Next transition can go wrong because of css leftover of previous transition

• Improved method calling through .backstretch('method', ...) to pass all arguments, and return value.
• Added current() function to return current slide index.

• Minor documentation improvements. Version release for updated docs in NPM etc.

• Minor fix: background css on the target element was sometimes cleared prematurely. (Issue #18)

• Minor fix: resolutionChangeRatioTreshold was a typo. Changed to resolutionChangeRatioThreshold, but keeping backwards compatibility.

• New: Added more transitions beside fade
• Bugfix: Youtube Iframe API's destroy was not being called
• Minor documentation updates

• New: Youtube and <video> support!

• Bugfix: Executing backstretch methods on already backstretched elements failed

• Published to bower under "jquery-backstretch-2"

• New alwaysTestWindowResolution option
• New resolutionRefreshRate option
• New resolutionChangeRatioTreshold option
• Minor bugfix: If there was no fade duration, the new image was still being removed asynchronously. Possibly causing a glitch if custom CSS is used.

• New alt image property
• New bypassCss option

• Changed multi-res feature width's meaning. width now means the actual width of the image to match against.
• Added pixelRatio option for multires.

• More granular control over options
• 1. Now you can specify alignX/alignY/duration/fade on an image basis
• 2. Minor bugfixes
• 3. Deprecated centeredX/centeredY

• Minor bug fixes due to latest PRs

• 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

• 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

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

• 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.