angular-retina

Replaces the AngularJS directive ng-src by a version which supports Retina displays.

If the browser runs on a Retina display and the referenced image is available in double resolution, then load the high resolution version of that image from the server.

Install

If you prefer to host Javascript files locally instead of using a CDN, install them with:

npm install angular-retina

Client usage

Into the main HTML code, add the required URLs from the CDN or include the files locally:

<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.2.9/angular.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/angular-retina/0.3.1/angular-retina.min.js"></script>

Please note, that angular-retina requires angularjs-1.2.1 or later.

In Javascript, initialize the main module for your AngularJS application:

var my_app = angular.module('MyApp', [...other dependencies..., 'ngRetina']);

In the body of any HTML code, access static referenced images using:

<img ng-src="/path/to/image.png" width="100" height="100">

or reference the image using AngularJS's markup:

<img ng-src="{{ image_url }}" width="100" height="100">

Note that when using this module, adding the element attributes width="..." and/or height="..." becomes mandatory, as the displayed image otherwise gets scaled to its double size.

Just use it in your HTML-code as you would use the common AngularJS directive ngSrc:

Alternative infix

When this library was written, Apple Inc. recommended to use @2x as infix, for images optimized for Retina displays. In late 2013, they changed their mind, and now suggest to use the infix _2x.

Since Apple's former recommendation, the proposed infix has been hard coded into some server-side libraries for image generation. Therefore, in version 0.3.0 of angular-retina, a configuration function has been added, which shall be used to set the infix to the newly proposed _2x – but of course only, if the server-side also supports it!

my_app.config(function(ngRetinaProvider) {
    ngRetinaProvider.setInfix('_2x');
});

Hide images until loaded, avoiding "broken image" display

To hide (opacity: 0) images until the library has determined what resolution to use, set the src and the image has finished downloading, use the following config:

my_app.config(function(ngRetinaProvider) {
    ngRetinaProvider.setFadeInWhenLoaded(true);
});

Images with embedded hash

When using a framework that embeds a digest/hash to the asset URL, the problem is that a high-resolution verison would have a different hash and would not follow the usual pattern that ends with @2x. Instead the hash is added at the end, i.e. /images/image@2x-{hash2}.jpg, so the automatic detection of image URL would fail.

The solution is to supply the high-resolution URL image from the outside of the library using the data-at2x attribute:

<img src="/images/image.jpg" data-at2x="/images/image@2x.jpg" />

On the server

Applications supporting Retina displays should include two separate files for each image resource. One file provides a standard-resolution version of a given image, and the second provides a high-resolution version of the same image. The naming conventions for each pair of image files is as follows:

• Standard: <image_name>.<filename_extension>
• High resolution: <image_name>@2x.<filename_extension>

If the browser runs on a high-resolution display, and if the referenced image is available in high-resolution, the corresponding <img ng-src="..."> tag is interpreted, such that the image in high-resolution is referenced.

This module can also be used to reference static image urls, to load the high resolution version on Retina displays.

Same Origin Policy

In order to verify if the image exists in high resolution, angular-retina invokes a HEAD request with the URL of the high-res image.

For security reasons, Javascript may not access files on servers starting with a different domain name. This is known as the Same Origin Policy. Therefore please ensure, that all images accessed through ng-src can be loaded from the same domain as the main HTML file.

Release History

• 0.1.0 - initial revision.
• 0.1.3 - fixed problems with minified JS code.
• 0.2.0 - using sessionStorage instead of $cacheFactory to boost performance.
• 0.3.0 - added setInfix to configure the used infix for Retina images.
• 0.3.1 - added a noretina attribute support to conditionally disable the "retinification" for an element.

License

© 2015 Jacob Rief

MIT licensed.