https://github.com/transitive-bullshit/rect-cover

Computes a transform between two rects just like background-size: cover.
https://github.com/transitive-bullshit/rect-cover

background-size cover rect rectangle

Last synced: 20 days ago
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Computes a transform between two rects just like background-size: cover.

• Host: GitHub
• URL: https://github.com/transitive-bullshit/rect-cover
• Owner: transitive-bullshit
• Created: 2018-03-16T23:47:06.000Z (almost 7 years ago)
• Default Branch: master
• Last Pushed: 2020-07-11T23:13:32.000Z (over 4 years ago)
• Last Synced: 2024-10-20T01:08:44.733Z (2 months ago)
• Topics: background-size, cover, rect, rectangle
• Language: JavaScript
• Homepage: https://transitive-bullshit.github.io/rect-cover/
• Size: 565 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: readme.md

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README

        
# rect-cover ([demo](https://transitive-bullshit.github.io/rect-cover/))

> Computes a transform between two rectangles the same way as `background-size: cover`.

[![NPM](https://img.shields.io/npm/v/rect-cover.svg)](https://www.npmjs.com/package/rect-cover) [![Build Status](https://travis-ci.com/transitive-bullshit/rect-cover.svg?branch=master)](https://travis-ci.com/transitive-bullshit/rect-cover) [![JavaScript Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://standardjs.com)

## Intro

Simulating `background-size: cover` is very useful for canvas animations, drawing sprites in games, and rendering videos. This module is used as part of our video rendering pipeline at [Automagical](https://automagical.ai/).

## Install

```bash

npm install --save rect-cover

```

## Usage

Check out the [demo](https://transitive-bullshit.github.io/rect-cover/) to understand what this module does.

```js

const rectCover = require('rect-cover')

const {

  scale,

  translate

} = rectCover({ width: 500, height: 500 }, { width: 1280, height: 720 })

// CSS transforms apply the rightmost operation first.

// Note that this assumes a transform-origin of `top left`.

const transform = `translate(${translate.x}px, ${translate.y}px) scale(${scale})`

```

## API

### rectCover(viewport, image)

Returns a 2D affine transform defined by `{ scale: Number, translate: { x: Number, y: Number } }` such that the given `image` will fully cover the `viewport` while maintaining its original aspect ratio.

Note that you'll want to apply the `scale` transform first followed by the `translate`.

#### viewport

Type: `{ width: Number, height: Number }`

The viewport you want to draw the image into.

#### image

Type: `{ width: Number, height: Number }`

The dimensions of the image to be drawn.

## Related

- [rect-contain](https://github.com/transitive-bullshit/rect-contain) is this module's sister, implementing `background-size: contain`.

- [rect-crop](https://github.com/gre/rect-crop) if you need to mimic rect-cover with a `zoom` ratio and `center` point (eg, for [kenburns effects](https://github.com/gre/kenburns))

- [css background-size](https://developer.mozilla.org/en-US/docs/Web/CSS/background-size)

## License

MIT © [Travis Fischer](https://github.com/transitive-bullshit)

Support my OSS work by following me on twitter