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