object-fit-math
v1.0.0
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Just the math behind object-fit and object-position
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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
andobject-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 fittedimg
/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 = (
parent: Size, child: Size,
fitMode: FitMode = 'fill', left = '50%', top = '50%'
) => Rect
transformFittedPoint = (
fittedPoint: Point, parent: Size, child: Size,
fitMode: FitMode = '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.