pixi-center

Center PIXI.Text, PIXI.Sprite, & PIXI.Container vertically and horizontally with ease. Actually you can center anything which inherits from PIXI.DisplayObject. It will round to the nearest pixel so your text stays sharp!

Install

npm i pixi-center

Importing

For convenience pixi-center will be automatically added to PIXI.displayObject which almost everything, including PIXI.Sprite and PIXI.Text, inerit from.

common.js

require('pixi.js')
require('pixi-center')

es6 modules

import pixi from 'pixi.js'
import pixiPause from 'pixi-center'

Usage

Methods

centerX

Center an object horizontally inside a container

mySprite.centerX(
    width,      // container width (Optional)
    options     // see options (Optional)
)

centerY

Center an object vertically inside a container

mySprite.centerY(
    height,     // container height (Optional)
    options     // see options (Optional)
)

centerXY

Center an object horizontally & vertically inside a container

https://jsfiddle.net/brenwell/ecad57kb/

mySprite.centerXY(
    width,      // container width (Optional)
    height,     // container height (Optional)
    options     // see options (Optional)
)

Center an object horizontally & vertically at a point

centerAt

https://jsfiddle.net/brenwell/zpk590p6/

mySprite.centerAt(
    coordinates, // Coordinates e.g. {x:10,y:30}
    options     // see options (Optional)
)

###Examples

Using the parent container to center

This is the simplest example. Pixi-center uses the parent's width and/or height if no options are passed. Which means, your object needs to be added to a container before calling centerXY, centerX or centerY.

const label = new PIXI.Text(text,style)
container.addChild(label)

// call after the object has been added to a child
label.centerXY()

Explictly supplying the bounds

This will center the text within a theoretical box of width:200 by height:300. Since you are providing the bounds it is not immportant to add the object to a container before calling centerXY, centerX or centerY.

const label = new PIXI.Text(text,style)
label.centerXY(200,300)

// can be added after
container.addChild(label)

Center one axis only

This will center the text vertically within a theoretical box of height:300, and then horizontally within the container,

const label = new PIXI.Text(text,style)

// center just the x axis within 500px
label.centerY(500)

container.addChild(label)

// center just the y axis with the parent container
label.centerY()

Center at a point

This will center the label at the given coordinate, regardless of anchor values.

const label = new PIXI.Text(text,style)
label.centerAt({x: 10, y: 10})

Options

The possible options are

const opts = {
    round: true, // default is true. Applies to all methods.
    anchorX: 0, // if not set will be taken from object if possible.
    anchorY: 0  // if not set will be taken from object if possible.
}

Round to pixel

By default pixi-center will place objects on whole pixels by rounding the result of the calculation. Which is great for text as it will be crystal clear. However at times this behaviour is unwanted. Passing an options object with round:false as the last argument will disable this.

label.centerX( null, {round: false} )
label.centerY( null, {round: false} )
label.centerXY( null, null, {round: false} )
label.centerAt( {x: 0, y: 0}, {round: false} )

Anchor positions

By default pixi-center will account for an element's anchor points when centering. But this can be overwritten if you wish by passing an options object with anchorX or anchorY set with values between 0-1 as the last argument. This will offset the centering.

label.centerX( undefined, {anchorX: 0} )
label.centerY( undefined, {anchorY: 0} )
label.centerXY( undefined, undefined, {anchorX: 0, anchorY: 0.5} )
label.centerAt( {x: 0, y: 0}, {anchorX: 0, anchorY: 0.5} )

Update on Resize

You can simply call any of the center functions on window.resize

window.onresize = (e) => label.centerXY()

Or for elements with an update method you could re-center when it is fired

mySprite.update = () => mySprite.centerXY()

Gotchas

Not centering in an empty PIXI.Container or my PIXI.Container keeps growing every time I center my object

PIXI.Containers have a width and height of 0 until something is placed inside them. If you want to center the text inside an empty container, it is best to add a PIXI.Graphics element first to give it some bounds

const container = new PIXI.Container()

const rectangle = new PIXI.Graphics()
rectangle.drawRect(0,0,100,100)
rectangle.alpha = 0 // if you dont want to see it
container.addChild(rectangle)

const label = new PIXI.Text('center me')
container.addChild(label)
container.centerXY()

To resize the container it is best to resize the rectangle instead