163 lines
4.8 KiB
Markdown
163 lines
4.8 KiB
Markdown
|
# PostCSS image-set() Function [<img src="https://postcss.github.io/postcss/logo.svg" alt="PostCSS Logo" width="90" height="90" align="right">][postcss]
|
|||
|
|
|||
|
[![NPM Version][npm-img]][npm-url]
|
|||
|
[![CSS Standard Status][css-img]][css-url]
|
|||
|
[![Build Status][cli-img]][cli-url]
|
|||
|
[<img alt="Discord" src="https://shields.io/badge/Discord-5865F2?logo=discord&logoColor=white">][discord]
|
|||
|
|
|||
|
[PostCSS image-set() Function] lets you display resolution-dependent images
|
|||
|
using the `image-set()` function in CSS, following the [CSS Images]
|
|||
|
specification.
|
|||
|
|
|||
|
[!['Can I use' table](https://caniuse.bitsofco.de/image/css-image-set.png)](https://caniuse.com/#feat=css-image-set)
|
|||
|
|
|||
|
```pcss
|
|||
|
.example {
|
|||
|
background-image: image-set(
|
|||
|
url(img.png) 1x,
|
|||
|
url(img@2x.png) 2x,
|
|||
|
url(img@print.png) 600dpi
|
|||
|
);
|
|||
|
}
|
|||
|
|
|||
|
/* becomes */
|
|||
|
|
|||
|
.example {
|
|||
|
background-image: url(img.png);
|
|||
|
}
|
|||
|
|
|||
|
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
|
|||
|
.example {
|
|||
|
background-image: url(img@2x.png);
|
|||
|
}
|
|||
|
}
|
|||
|
|
|||
|
|
|||
|
@media (-webkit-min-device-pixel-ratio: 6.25), (min-resolution: 600dpi) {
|
|||
|
.example {
|
|||
|
background-image: url(my@print.png);
|
|||
|
}
|
|||
|
}
|
|||
|
|
|||
|
.example {
|
|||
|
background-image: image-set(
|
|||
|
url(img.png) 1x,
|
|||
|
url(img@2x.png) 2x,
|
|||
|
url(img@print.png) 600dpi
|
|||
|
);
|
|||
|
}
|
|||
|
```
|
|||
|
|
|||
|
## Usage
|
|||
|
|
|||
|
Add [PostCSS image-set() Function] to your project:
|
|||
|
|
|||
|
```bash
|
|||
|
npm install postcss-image-set-function --save-dev
|
|||
|
```
|
|||
|
|
|||
|
Use [PostCSS image-set() Function] as a [PostCSS] plugin:
|
|||
|
|
|||
|
```js
|
|||
|
const postcss = require('postcss');
|
|||
|
const postcssImageSetFunction = require('postcss-image-set-function');
|
|||
|
|
|||
|
postcss([
|
|||
|
postcssImageSetFunction(/* pluginOptions */)
|
|||
|
]).process(YOUR_CSS /*, processOptions */);
|
|||
|
```
|
|||
|
|
|||
|
[PostCSS image-set() Function] runs in all Node environments, with special
|
|||
|
instructions for:
|
|||
|
|
|||
|
| [Node](INSTALL.md#node) | [PostCSS CLI](INSTALL.md#postcss-cli) | [Webpack](INSTALL.md#webpack) | [Create React App](INSTALL.md#create-react-app) | [Gulp](INSTALL.md#gulp) | [Grunt](INSTALL.md#grunt) |
|
|||
|
| --- | --- | --- | --- | --- | --- |
|
|||
|
|
|||
|
## Options
|
|||
|
|
|||
|
### preserve
|
|||
|
|
|||
|
The `preserve` option determines whether the original declaration using
|
|||
|
`image-set()` is preserved. By default, it is preserved.
|
|||
|
|
|||
|
```js
|
|||
|
postcssImageSetFunction({ preserve: false })
|
|||
|
```
|
|||
|
|
|||
|
```pcss
|
|||
|
.example {
|
|||
|
background-image: image-set(
|
|||
|
url(img.png) 1x,
|
|||
|
url(img@2x.png) 2x,
|
|||
|
url(img@print.png) 600dpi
|
|||
|
);
|
|||
|
}
|
|||
|
|
|||
|
/* becomes */
|
|||
|
|
|||
|
@media (-webkit-min-device-pixel-ratio: 1), (min-resolution: 96dpi) {
|
|||
|
.example {
|
|||
|
background-image: url(img.png);
|
|||
|
}
|
|||
|
}
|
|||
|
|
|||
|
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
|
|||
|
.example {
|
|||
|
background-image: url(img@2x.png);
|
|||
|
}
|
|||
|
}
|
|||
|
|
|||
|
|
|||
|
@media (-webkit-min-device-pixel-ratio: 6.25), (min-resolution: 600dpi) {
|
|||
|
.example {
|
|||
|
background-image: url(my@print.png);
|
|||
|
}
|
|||
|
}
|
|||
|
```
|
|||
|
|
|||
|
### onvalid
|
|||
|
|
|||
|
The `oninvalid` option determines how invalid usage of `image-set()` should be
|
|||
|
handled. By default, invalid usages of `image-set()` are ignored. They can be
|
|||
|
configured to display a `warning` or `throw` an error.
|
|||
|
|
|||
|
```js
|
|||
|
postcssImageSetFunction({ oninvalid: 'warning' }) // warn on invalid usages
|
|||
|
```
|
|||
|
|
|||
|
```js
|
|||
|
postcssImageSetFunction({ oninvalid: 'throw' }) // throw on invalid usages
|
|||
|
```
|
|||
|
|
|||
|
## Image Resolution
|
|||
|
|
|||
|
The `image-set()` function allows an author to provide multiple resolutions of
|
|||
|
an image and let the browser decide which is most appropriate in a given
|
|||
|
situation. The `image-set()` also never fails to choose an image; the
|
|||
|
`<resolution>` just helps determine which of the images is chosen.
|
|||
|
|
|||
|
Since this plugin is not a browser, the image options are sorted by device
|
|||
|
pixel ratio and the lowest ratio is used as the default, while the remaining
|
|||
|
images are pushed behind media queries.
|
|||
|
|
|||
|
Therefore, this plugin can only approximate native browser behavior. While
|
|||
|
images should typically match the resolution as the device they’re being viewed
|
|||
|
in, other factors can affect the chosen image. For example, if the user is on a
|
|||
|
slow mobile connection, the browser may prefer to select a lower-res image
|
|||
|
rather than wait for a larger, resolution-matching image to load.
|
|||
|
|
|||
|
[cli-img]: https://github.com/csstools/postcss-plugins/workflows/test/badge.svg
|
|||
|
[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
|
|||
|
[css-img]: https://cssdb.org/images/badges/image-set-function.svg
|
|||
|
[css-url]: https://cssdb.org/#image-set-function
|
|||
|
[discord]: https://discord.gg/bUadyRwkJS
|
|||
|
[npm-img]: https://img.shields.io/npm/v/postcss-image-set-function.svg
|
|||
|
[npm-url]: https://www.npmjs.com/package/postcss-image-set-function
|
|||
|
|
|||
|
[CSS Images]: https://drafts.csswg.org/css-images-4/#image-set-notation
|
|||
|
[Gulp PostCSS]: https://github.com/postcss/gulp-postcss
|
|||
|
[Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss
|
|||
|
[PostCSS]: https://github.com/postcss/postcss
|
|||
|
[PostCSS Loader]: https://github.com/postcss/postcss-loader
|
|||
|
[PostCSS image-set() Function]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-image-set-function
|