https://github.com/strues/retinajs

JavaScript, SCSS, Sass, Less, and Stylus helpers for rendering high-resolution image variants
https://github.com/strues/retinajs

dpi image javascript retina

Last synced: 3 days ago
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JavaScript, SCSS, Sass, Less, and Stylus helpers for rendering high-resolution image variants

• Host: GitHub
• URL: https://github.com/strues/retinajs
• Owner: strues
• License: mit
• Created: 2012-04-04T20:37:09.000Z (over 12 years ago)
• Default Branch: master
• Last Pushed: 2020-03-14T13:18:57.000Z (almost 5 years ago)
• Last Synced: 2024-10-29T15:05:06.305Z (about 2 months ago)
• Topics: dpi, image, javascript, retina
• Language: CSS
• Homepage: http://retinajs.com
• Size: 2.59 MB
• Stars: 4,422
• Watchers: 127
• Forks: 612
• Open Issues: 43
• Metadata Files:
  • Readme: README.md
  • Contributing: CONTRIBUTING.md
  • License: LICENSE
  • Code of conduct: .github/CODE_OF_CONDUCT.md

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README

        
# retina.js

[![npm version](https://badge.fury.io/js/retinajs.png)](https://badge.fury.io/js/retinajs) [![styled with prettier](https://img.shields.io/badge/styled_with-prettier-ff69b4.svg)](https://github.com/prettier/prettier)  [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/) [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/strues/retinajs/master/LICENSE)

### JavaScript, Sass, Less, and Stylus helpers for rendering high-resolution image variants

`retina.js` makes it easy to serve high-resolution images to devices with displays that support them. You can prepare images for as many levels of pixel density as you want and let `retina.js` dynamically serve the right image to the user.

## How it works

There are 4 ways to use `retina.js`:

1. Automatically swapping out `src` paths on `img` tags.

2. Automatically swapping out background image URLs in inline styles.

3. Manually specifying the location of a high-res image variant (works for `src` attributes and inline styles).

4. Automatically creating media queries for CSS background images.

#### Img Tags

`retina.js` assumes you are using Apple's prescribed high-resolution modifiers (@2x, @3x, etc) to denote high-res image variants on your server. It also assumes that if you have prepared a variant for a given high-res environment, that you have also prepared variants for each environment below it. For example, if you have prepared 3x variants, `retina.js` will assume that you have also prepared 2x variants.

With this in mind, you'll specify your highest environment level with the `data-rjs` attribute and let `retina.js` take it from there.

Let's say you have an image on your page that looks like this:

```html



```

In this case, we've set our resolution cap at "3", denoting that we've prepared 3x and 2x image variants. When the page loads, `retina.js` will check the actual resolution of the device environment to decide whether it should really serve up a 3x image. If the user happens to be in a 2x environment, `retina.js` will serve up the 2x image instead, assuming it will find the image at `/images/[email protected]`.

If the environment does have 3x capabilities, `retina.js` will serve up the 3x image. It will expect that url to be `/images/[email protected]`. If the environment has the ability to display images at higher densities than 3x, `retina.js` will serve up the image of the highest resolution that you've provided, in this case 3x.

#### Inline Styles

Previous versions of `retina.js` were unable to target background images set via inline styles. Now, if you apply a `data-rjs` attribute to any kind of element other than an `img`, the script will target inline background images instead of `src` attributes.

So if you created an element like this:

```html



```


`retina.js` would convert it to something like this:

```html



```


The logic behind image swapping is exactly the same when dealing with background images as it is when dealing with `src` attributes. If the user's environment only supports 2x variants, `retina.js` will load the 2x variant instead of the 3x.

_Note that it is up to you in a case like this to correctly apply background sizing and any other necessary background-related styles to the element. retina.js will not affect these._

#### Manually Specifying a High-Res URL

In previous versions, you could tell the script where to find your high-res file by using the `data-at2x` attribute. Now, if you pass a URL to the `data-rjs` attribute, `retina.js` will use the image at the path you specify for all high-resolution environments instead of trying to dynamically serve an auto-suffixed image path based on the environment's capabilities. This will work for both `src` attributes on `img` tags and inline background images on all other tags.

For example, you might write something like this:

```html







```


If the user then loads the page in any kind of high-resolution environment, they'll get the following:

```html







```


#### Media Queries

`retina.js` comes with mixins for SCSS, Sass, Less, and Stylus. These mixins work similarly to the JavaScript version in that they will dynamically serve images for as many high-res environments as you've prepared image variants for. Previously, these mixins were named "at2x" but because they now serve images for multiple environments, they have been renamed "retina".

In each language, the retina mixin allows 4 parameters:

1. `path` - The path to your standard resolution image.

2. `cap` - _Optional._ The highest resolution level for which you have prepared images. Defaults to 2.

3. `size`- _Optional._ A value to be applied to the `background-size` property. Defaults to `auto auto`.

4. `extras`- _Optional._ Any other values to be added to the background property. Defaults to nothing.

Here is an example wherein we are specifying that we have prepared images for both 2x and 3x environments:

**SCSS**

```scss

#item {

  @include retina('/images/my_image.png', 3, cover, center center no-repeat);

}

```

**Sass**

```sass

#item

  +retina('/images/my_image.png', 3, cover, center center no-repeat)

```

**Less**

```less

#item {

  .retina('/images/my_image.png', 3, cover, center center no-repeat);

}

```

**Stylus**

```stylus

#item

  retina('/images/my_image.png', 3, cover, center center no-repeat)

```

Regardless of the dialect, the output is effectively the same:

```css

#item {

  background: url("/images/my_image.png") center center no-repeat;

  background-size: cover;

}

@media all and (-webkit-min-device-pixel-ratio: 1.5),

       all and (-o-min-device-pixel-ratio: 3 / 2),

       all and (min--moz-device-pixel-ratio: 1.5),

       all and (min-device-pixel-ratio: 1.5) {

  #item {

    background: url("/images/[email protected]") center center no-repeat;

    background-size: cover;

  }

}

@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {

  #item {

    background: url("/images/[email protected]") center center no-repeat;

    background-size: cover;

  }

}

@media (-webkit-min-device-pixel-ratio: 3), (min-resolution: 288dpi) {

  #item {

    background: url("/images/[email protected]") center center no-repeat;

    background-size: cover;

  }

}

```

## Compatibility

`retina.js` is compatible with all modern browsers and __should__ not throw errors in old browsers all the way back through IE6.

## Installing & Launching

### JavaScript

There are 2 ways to use the JavaScript version of `retina.js`:

1. The old-school way (manually dropping the script into an html file).

2. The new-school way (importing it into a larger JavaScript build process).

#### Old-School

To use retina.js the old-school way, download **retina.min.js** and put it on your server. Then, include the script in your html file at the bottom of your template, before your closing \