rect-cover (demo)

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

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.

Install

npm install --save rect-cover

Usage

Check out the demo to understand what this module does.

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 is this module's sister, implementing background-size: contain.
• rect-crop if you need to mimic rect-cover with a zoom ratio and center point (eg, for kenburns effects)
• css background-size

License

MIT © Travis Fischer

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