Staffelei

Staffelei is a utility class that makes working with the 2D Canvas API (CanvasRenderingContext2D) easier. The Staffelei class extends the Leinwand. Thus you get all the method chaining goodness form there. Additionally Staffelei provides more utilify methods, event handeling, as well as multi layer canvases.

There are two ways to use Staffelei. Either you use it in the same way as Leinwand. Simply as a wrapper around a canvas. Or you also use it to manage layers.

In the first case (called simple-mode) you'd do something like this:

import Staffelei from 'staffelei';
//or
const Staffelei = require('staffelei');

let s = new Staffelei(document.getElementById('myCanvas'));

s
  .fillStyle('red')
  .mt(20,20)
  //...

Where the element with the id myCanvas is a canvas.

If you want to use the layers you use layered-mode.

let s = new Staffelei(document.getElementById('myContainer'), { mode: 'layered' ,
                                                                width: 500 ,
                                                                height: 500  });

s
  .createLayer('background')
  .fillRectCenteredAt(200,200, 20, 30)
  .createLayer('foreground')
  //...

In this case the element with the id myContainer is the element (e.g. a div) in which the canvas will be placed by Staffelei.

Methods

All the methods from Leinwand are available.

s.on(eventName, listener)

This registers an eventlistener. The available events are:

Events with synonyms
mouseup
mousedown
mousemove
mouseover, mousein
mouseleave, mouseout
click
leftclick
contextmenu, rightclick

so for example if you want to draw a square where a user clicks on the canvas:

s.on('click', e => {
  s.fillRectCenteredAt(e.x,e.y,10,10);
});

The event object you get for all of the events looks like this:

Property	Description
x	the x coordinate of the event relative to the canvas
y	the y coordinate of the event relative to the canvas
target	the canvas the event belongs to (The target you passed into the constructor)
event	the original DOM event emitted on the eventSource
button	the button property from the event
preventDefault	a function that calles preventDefault on the event

s.once(eventName, listener)

like s.on except the listener is only called once.

s.isMouseDown(button)

Returns true if the mouse button with button number button is currently down. button defaults to 1 which is the left mouse button. Since this method does not need any state from the Staffelei object it can also be called staticaly like Staffelei.isMouseDown(button).

Methods for layered-mode

These methods only work when Staffelei is used in layered-mode and will throw an Error if used in simple-mode.

s.createLayer(name, {position})

Creates a new layer with the name name and the position in the stack of layers. Also sets the newly created layer as the current layer.

layer(name)

Switch the current layer to the layer with the name name. If no layer with that name exists this throws an Error.

doFullscreen()

Enter fullscreen.

exitFullscreen()

Exist fullscreen.

Getting Staffelei

The easiest way to use Staffelei is to use the npm package and the use it with some tool like browserify or rollup.

If you'd rather just get a .js file you can download it from the releases page. There are two versions available there. One built with rollup and one built with browserify. The rollup version is smaller but the browserify version is probably more compatible with older browsers since more of the code has been transpiled.

Release History

• 2018-05-06   v0.1.1   documentation
• 2018-02-23   v0.1.0   add layer management
• 2018-02-09   v0.0.1   initial version