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    object-fit-math
    TypeScript icon, indicating that this package has built-in type declarations

    1.0.0 • Public • Published

    object-fit-math

    Just the math behind object-fit and object-position

    It has no dependencies and just exposes a few simple functions

    Allows you to use the same math as the browser uses for object-fit and object-position

    Supports the following object-fit properties:

    contain, cover, fill, none, scale-down

    Supports object-position specified in px or % only

    Use cases:

    • using the same algorithm as the browser elsewhere, like on an HTML canvas or server side image rendering
    • finding out the bounds for an object that's using object-fit and object-position - this is what I actually wrote this for, so I could translate the mouse/touch event locations to the actual pixel location on a fitted img/canvas/video element
    • you could use it to make a polyfill I guess

    usage

    npm install object-fit-math

    basic usage

    const { fit, position, fitAndPosition } = require( 'object-fit-math' )
     
    const parentSize = { width: 320, height: 240 }
    const childSize = { width: 90, height: 160 }
     
    const fitted = fit( parentSize, childSize, 'contain' )
     
    // { width: 135, height: 240 }
    console.log( fitted )
     
    const positioned = position( parentSize, fitted, '50%', '50%' )
     
    // { x: 92.5, y: 0 }
    console.log( positioned )
     
    const rect = fitAndPosition( parentSize, childSize, 'contain', '50%', '50%' )
     
    // { x: 92.5, y: 0, width: 135, height: 240 }
    console.log( rect )

    translate a point on the fitted element to original pixel location

    const { transformFittedPoint } = require( 'object-fit-math' )
     
    // get the object eg a canvas that uses object-fit from the DOM here
     
    canvas.addEventListener( 'click', e => {
      const { offsetX: x, offsetY: y } = e
     
      const canvasSize = canvas.getBoundingClientRect()
      const { objectFit, objectPosition } = getComputedStyle( canvas )
      const [ left, top ] = objectPosition.split( ' ' )
     
      const childPoint = transformFittedPoint(
        { x, y }, canvasSize, canvas, objectFit, left, top
      )
     
      console.log( childPoint )
    })

    types

    See /src/types.ts for Size, Point etc

    exported functions

    fit = ( parent: Size, child: Size, fitMode: FitMode = 'fill' ) => Size
     
    position = ( parent: Size, child: Size, left = '50%', top = '50%' ) => Point
     
    fitAndPosition = (
      parentSize, childSize,
      fitModeFitMode = 'fill', left = '50%', top = '50%'
    ) => Rect
     
    transformFittedPoint = (
      fittedPointPoint, parentSize, childSize,
      fitModeFitMode = 'fill', left = '50%', top = '50%'
    ) => Point
     
    isFit = ( value: any ): value is FitMode => boolean

    examples

    transform event point to pixel

    The transform example creates a small canvas then fits it to its parent element - you can then click anywhere on the canvas to get the actual pixel location. Useful for finding out the actual pixel that was clicked on a video/canvas/img which uses object-fit

    compare

    The compare example generates a long list of combinations of parent and child sizes, fit modes, positions etc

    Each comparison shows the result of the DOM's built in object-fit and object-position on the left, and on the right it uses this module to get the rectangle and uses absolute positioning and sizing to replicate the effect

    building

    You will need typescript installed globally to build the module, and browserify installed globally to build the examples

    npm install typescript -g

    npm run build

    npm install browserify -g

    npm run build-examples

    contributing

    Please try to follow the existing style (sorry, no linting etc at the moment) and keep your pull requests small and focussed

    testing your changes

    The easiest way to tell if your changes are correct is to build the examples and then scroll through the compare example - yes, this file is huge, but it ensures that a good combination of inputs is represented. Once you verify visually that the math matches the DOM behaviour, there is a <pre> element at the bottom that contains the fixture data used by the tests, copy and paste this to /src/test/fixtures.json and run the tests.

    license

    MIT License

    Copyright (c) 2020 Nik Coughlin

    Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

    Install

    npm i object-fit-math

    DownloadsWeekly Downloads

    2,403

    Version

    1.0.0

    License

    MIT

    Unpacked Size

    2.32 MB

    Total Files

    66

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