e2d

e2d.js

An es2015/es5 declarative canvas renderer.

Introduction

Most canvas libraries abstract away different aspect of canvas to make you faster. When using this library, there isn't much abstraction. In fact, the API mirrors the canvas2d API in a way makes coding canvas fun! Much like react uses a render function to make changes to the DOM in an abstract way, so does e2d to the canvas context.

Getting Started

With react.js, the developer calls React.render once to start up the application. Since e2d does not work with the DOM, there are no bindings internally to have a meaningful event lifecycle. This means that e2d.render must be called every frame. Take the following "Hello World" example:

let canvas = document.createElement('canvas');
canvas.width = 800;
canvas.height = 600;
 
//get the canvas context
let ctx = canvas.getContext('2d');
 
//add the canvas to the dom
document.body.appendChild(canvas);
 
//for commonjs, browserify, webpack
let e2d = require('e2d');
 
//use this if the application requires user input on the canvas
e2d.initialize(ctx);
 
//requestAnimationFrame loop will call this function once per frame
//it is not necessary to use this convenience function provided by e2d
e2d.raf(() => {
 
  //e2d.render accepts an unlimited number of arguments and the last one must be the canvas context
  return e2d.render(
    e2d.clearRect(canvas.width, canvas.height),
    e2d.fillText("Hello World!", 100, 100),
    ctx
  );
});

There is also a babel plugin for e2dx elements so that developing on canvas can be more like using SVG in javascript. It's located here and looks like this:

 
//always call this ONCE to obtain mouse, activeRegion, and keyboard support
e2d.initialize(ctx);
 
//raf will call the provided function every frame
e2d.raf(() => {
  //get the mouse position
  let { x, y } = e2d.mouseData(ctx);
 
  //use the translate element to move the point of origin
  return <render ctx={ctx}>
    <clearRect width={canvas.width} height={canvas.height} />
    <translate x={x} y={y}>
      <fillText text="Hello World!" />
    </translate>
  </render>;
  );
});

Instruction variables

e2d introduces "Instruction variables" that represent more complex canvas instructions. They are similar to virtual dom elements in react.

For example, all canvas instructions can be variables and stored for later use. This speeds up execution time and reduces memory usage.

//create a fill command that always fills red
let fillRed = e2d.fillStyle('red', e2d.fill());
 
//create a 6 sided polygon with radius 10 at [0,0]
let hexagonShape = e2d.createRegularPolygon(10, [0,0], 6);
 
//e2d.path will wrap the instructions passed to it with beginPath and closePath
let hexagonPath = e2d.path(
    //convenience function to map coordinates to ctx.moveTo, and ctx.lineTo
    hexagonShape.map(e2d.moveToLineTo)
);
 
//combine the path and fill instructions in an array
let redHexagon = [ hexagonPath, fillRed ];

Mix and match different canvas commands to make code more expressive and easier to read. For example, using the redHexagon variable in the above example to get started:

//create a canvas first...
e2d.raf(() => {
  return e2d.render(
    //clear the canvas every frame
    e2d.clearRect(canvas.width, canvas.height), //e2d knows that x=0 and y=0 are default parameters
 
    //move the hexagon center point to the center of the canvas
    e2d.translate(0.5 * canvas.width, 0.5 * canvas.height,
      redHexagon
    ),
 
    //render it to the canvas context
    ctx
  );
})
 

Performance

The goal of e2d is to be fast. It has gone under numerous refactors to increase the speed of each canvas property. On top of engine performance, there is an additional benefit to using instruction variables. Using these will result in less user-defined function calls. With instruction storage, and less user defined function calls, the majority of the application view layer will sit around in memory waiting to be parsed every frame.

Most importantly, creating an entire render tree every frame has a relatively minimal performance impact.

Drawing Collections

Collections are harder to optimize, so try to make data flow into instruction variables. See the following example:

import e2d from 'e2d';
let particles = [];
for(let i = 0; i < 100; i++) {
  particles.push({ //create some particles
    x: Math.random() * config.width,
    y: Math.random() * config.height,
    r: 1
  });
}
 
//fillArc has default function parameters [x=0, y=0, beginRadians=0, endRadians=Math.PI*2]
let particleShape = e2dfillArc(1); //only the radius is provided
 
//later
e2d.raf(() => {
  let particleMap = [], particle;
 
  //loop over each particle using a for loop
  for(let i = 0; i < particles.length; i++) {
    particle = particles[i];
 
    //move them 1 pixel per frame
    particle.y += 1;
 
    //loop the particle
    if (particle.y > config.height) {
      particle.y = 0;
    }
 
    particleMap.push(
      e2d.translate(particle.x, particle.y, //move to the particle position
        e2d.scale(particle.r, particleShape) //scale the particle
      )
    );
  }
 
  return e2d.render(
    e2d.clearRect(config.width, config.height),
    e2d.fillStyle('blue', particleMap), // every particle is blue in this case
    ctx
  );
});

Getting started

I highly recommend using webpack or browserify in node.js to modularize your code, but the fastest way to get started is to use the e2d.compat.min.js file in the /dist/ folder, or e2d.min.js for native es2015 support.

Import using script method

<script src="e2d.compat.min.js" type="text/javascript"></script>

webpack-dev-server

Please see webpack-dev-server for all your web development server needs.

API

e2d.render

This is the command that actually draws to the canvas. Create some drawing instructions and pass them to this function.

import e2d from 'e2d';
 
//create a draw command
let helloWorld = e2d.translate(200, 200,
  e2d.fillText("Hello World!")
);
 
//create a canvas
let canvas = doucment.createElement('canvas');
canvas.width = 400;
canvas.height = 400;
document.body.appendChild(canvas);
 
let ctx = canvas.getContext('2d');
 
e2d.raf(
  //draw something every frame
  () => e2d.render(
    e2d.clearRect(400, 400),
    helloWorld,
    ctx //ctx must be the last parameter
  )
);

extend.js

For use with custom instructions.

import { Instruction, extend } from 'e2d';
 
let extensions = {
  //first argument is props, second is the canvas context.
  drawSprite({ x, y, size, rotation, texture }, ctx) {
    ctx.save();
    ctx.translate(x, y);
    ctx.scale(size, size);
    ctx.drawImage(texture, 0, 0, texture.width, texture.height);
    //always make sure to restore canvas context state to prevent render side-effects
    ctx.restore();
  }
}
 
//to use it, pass an Instruction object to e2d.render
e2d.render(
  new Instruction('drawSprite', { x, y, size, rotation, texture }),
  ctx
);
 
 

Render Commands

The following render commands are provided to you in this library.

arc.js

Arcs have 5 forms, and correspond to the documentation here at mdn:

import e2d from 'e2d';
 
let fastestArc = e2d.arc(); //radius 1 and x, y is 0, 0
let justRadius = e2d.arc(radius); //radius is set, x, y is 0
let radiusWithXY = e2d.arc(x, y, radius); //radius is set, x, y is [x], [y]
 
//to specify the start and end angle, use the startAngle and endAngle parameters
let radiusWithXYandAngles = e2d.arc(x, y, radius, startAngle, endAngle);
 
//to specify anticlockwise motion, use the anticlockwise parameter like this
let arcAntiClockwise = e2d.arc(x, y, radius, startAngle, endAngle, anticlockwise);

arcTo.js

For information on how the arcTo function works, see mdn.

let arcToInstruction = e2d.arcTo(x1, y1, x2, y2, r);
 
//don't forget to wrap the arcTo function in the path function
let pathInstruction = e2d.path(
  e2d.arcTo(x1, y1, x2, y2, r)
);

beginPath.js

It's possible to control when a path begins manually by using the beginPath function.

let beginPathOperation = e2d.beginPath();

bezierCurveTo.js

See mdn for information on how to use Bezier curves.

//cp1 and cp2 are control points  and the curve ends at [x, y]
let myCurve = e2d.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);

clearRect.js

To see how clearRect works, see mdn. The clearRect function has two forms.

 
//to specify a rectangle at [0,0] use the clearRect shorthand
let widthAndHeight = e2d.clearRect(width, height);
 
//otherwise, specify x and y
let sizeAndPosition = e2d.clearRect(x, y, width, height);
 

clip.js

This provides a clipping region for child instructions.

In order to draw a clipped image, for instance, use the clip function with a path. For more information on clipping, please visit mdn.

Please note that the path cannot be wrapped in the e2d.path() function because clip will automatically close the path provided.

 
//create a hexigon with radius 200 and map it to a set of moveTo and lineTo instructions
let region = e2d.createRegularPolygon(200, [0, 0], 6).map(e2d.moveToLineTo);
 
//this results in a polygonal cliped drawImage command
let clippedImage = e2d.clip(
  region, //must be the first argument
 
  //center the image at [0,0] to see it
  e2d.translate(-img.width * 0.5, -img.height * 0.5,
    e2d.drawImage(img)
  )
);
 

imageSmoothingEnabled.js

This function is wrapper function that sets imageSmoothingEnabled for it's children. (default is true)

For more information on how imageSmoothingEnabled works, please visit mdn.

let noSmooth = e2d.imageSmoothingEnabled(false,
  ...children
);

drawImage.js

This function draws an image to the canvas when rendered.

See mdn for more information on how to use drawImage.

Note to chrome developers, it's faster to use a image pattern and fill a rectangle using a fillStyle or imagePattern.

 
//one paramenter means draw the image at 0, 0 with img.width and img.height as the width/height parameters
let imgCommand = e2d.drawImage(img);
 
let imgCommandPosition = e2d.drawImage(img, x, y); //draw image at x, y, img.width, img.height
 
let imgCommandSize = e2d.drawImage(img, x, y, width, height); //specify the size of the image
 
//or draw the image from a source within the image (this is hard to optimize for the browser and may be slow)
let imgSourceSize = e2d.drawImage(img, sx, sy, sWidth, sHeight, x, y, width, height);

ellipse.js

This will add an ellipse to the current path. This method is "pseudo-polyfilled" and supported for all browsers. For more information on this method please visit mdn. There are three forms for the ellipse function.

Please see mdn for more information on this experimental technology.

 
let example = e2d.ellipse(radiusX, radiusY); //from 0, 0
let example2 = e2d.ellipse(x, y, radiusX, radiusY); // from x, y
let example3 = e2d.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise);

fillArc.js

This method was added for convenience. It makes the API a bit more consistent and takes the same parameters as the arc function and works exactly like fillRect.

import e2d from 'e2d';
 
let fastestArc = e2d.fillArc(); //radius 1 and x, y is 0, 0
let justRadius = e2d.fillArc(radius); //radius is set, x, y is 0
let radiusWithXY = e2d.fillArc(x, y, radius); //radius is set, x, y is [x], [y]
 
//to specify the start and end angle, use the startAngle and endAngle parameters
let radiusWithXYandAngles = e2d.fillArc(x, y, radius, startAngle, endAngle);
 
//to specify anticlockwise motion, use the anticlockwise parameter like this
let arcAntiClockwise = e2d.fillArc(x, y, radius, startAngle, endAngle, anticlockwise);

fillRect.js

To see how fillRect works, see mdn. The fillRect function has two forms.

 
//to specify a rectangle at [0,0] use the fillRect shorthand
let widthAndHeight = e2d.fillRect(width, height);
 
//otherwise, specify x and y
let sizeAndPosition = e2d.fillRect(x, y, width, height);
 

fillStyle.js

This function will "set" the fillStyle property using the first argument as the value for the property. To see how fillStyle works visit mdn.

 
//fill a red circle
let redCircle = e2d.fillStyle('red',
  e2d.fillArc(200)
);

Nested fill styles can occur (and stack as a result):

let example = e2d.fillStyle('red',
  //fillStyle is red here
  e2d.fillStyle('blue',
    //fillStyle is blue here
  )
  //now it's red again
);

strokeStyle.js

This function will "set" the strokeStyle property using the first argument as the value for the property. To see how strokeStyle works visit mdn.

 
//fill a red circle
let redCircle = e2d.strokeStyle('red',
  e2d.strokeArc(200)
);

Nested stroke styles can occur (and stack as a result):

let example = e2d.strokeStyle('red',
  //strokeStyle is red here
  e2d.strokeStyle('blue',
    //strokeStyle is blue here
  )
  //now it's red again
);

globalCompositeOperation.js

For change global composite operations, use globalCompositeOperation().

See mdn: globalCompositeOperation to learn how to use them.

let operation = e2d.globalCompositeOperation('multiply',
  //do some fill operations
);

globalAlpha.js

The globalAlpha function will apply and set the globalAlpha relative to the parent globalAlpha value.

 
let alphaCommands = e2d.globalAlpha(0.5,
  //children are now drawn at 0.5 alpha
 
  e2d.globalAlpha(0.5,
    //children are now drawn at 0.25 alpha because 0.5 * 0.5 is 0.25  (floating point math applies)
  )
)
 

hitRegion.js and hitRect.js

The hitRect and hitRegion functions will apply a hitRegion to the canvas.

Hit regions are complicated, because they are relative to the current state of the canvas context.

let hexagon = e2d.createRegularPolygon(100, [0, 0], 6);
 
let hexagonPath = e2d.path(
  hexagon.map(e2d.moveToLineTo)
);
 
e2d.initialize(ctx);
e2d.raf(() => {
  let regions = e2d.regions(ctx);
 
  return e2d.render(
    e2d.translate(100, 100,
 
      //if there is a hovered region, turn the fillStyle red
      e2d.fillStyle(regions.length > 0 ? 'red' : 'black',
 
        //fill a hexagon
        hexagonPath, e2d.fill(),
 
        //set the hexagon region on the canvas
        e2d.hitRegion('hexagon-region', hexagon)
      )
    ),
    ctx
  );
});
 

To make a square use hitRect(id, x, y, width, height) or hitRect(id, width, height).

invertMatrix.js

This function will return an inverse matrix relative to the canvas matrix provided by calculating a determinant and returning a new Array.

This function is used internally to transform mouse points inversely to determine point in polygon detection relative to the provided shape.

let [a, b, c, d, e, f] = e2d.invertMatrix([a, b, c, d, e, f]);

lineStyle.js

This is a composite property abstraction that contains lineWidth and other useful properties. See mdn: lineCap, mdn: lineWidth, mdn: lineJoin, mdn: miterLimit, and mdn: setLineDash

let style = {
  lineWidth: 1,
  lineCap: 'round',
  lineJoin: 'bevel',
  miterLimit: 10,
  lineDash: [],
  lineDashOffset: 0
};

lineDashOffset and lineDash are abstracted to make them easier to animate.

let example = e2d.lineStyle(style,
  //do some line stroke() operations here
);

path.js, lineTo.js and moveTo.js

The path(pathInstructions) call wraps pathInstructions in beginPath() and endPath() operations.

To see how these functions work, visit mdn for moveTo, and lineTo.

//wrap paths in e2d.path()
let example = e2d.path(
  e2d.moveTo(0, 0),
  e2d.lineTo(10, 10),
  e2d.lineTo(10, 0)
);
 

quadraticCurveTo.js

Use this to make a quadratic curve to another point. All 4 parameters are required. To see how this function works, please visit mdn.

 
let curveCommand = e2d.quadraticCurveTo(cpx, cpy, x, y);

rotate.js, translate.js, and scale.js

Use these functions to translate/rotate/and scale the provided context.

These are the most important functions abstracted by the e2d render engine. Internally e2d uses setTransform on the canvas and keeps track of transforms manually. This allows the developer to use transforms like rotate and scale without worrying about permanently displacing a canvas context.

The rotate function uses radians like this.

let rotatedSquare = e2d.rotate(Math.PI / 8, //45 degrees
  e2d.path(e2d.rect), e2d.stroke()
);

To translate a draw command, use the translate function with the x and y parameters.

//fill a circle at [x, y] with radius 100
let movedCircle = e2d.translate(x, y, e2d.fillArc(100));

To scale a draw command, use the `scale function. It has two forms.

//scale a rectangle to double it's size
let doubleSized = e2d.scale(2, e2d.fillRect(10, 10));
 
//scale the rectangle by [x, y]
let doubleSizedXOnly = e2d.scale(x, y, e2d.fillRect(10, 10));

As a final example, a default drawSprite function is provided here.

//standard sprite function
let drawSprite = (sprite, { position, size, rotation, center }) => e2d.translate(position[0], position[1],
  //rotate before scaling to prevent side effects
  e2d.rotate(rotation,
    e2d.scale(size,
      //center the sprite
      e2d.translate(-center[0], -center[1],
        sprite
      )
    )
  )
);
 
//this is how it's used
e2d.render(
  drawSprite(e2d.drawImage(img), {
    position: [100, 100],
    size: 1.1,
    rotation: Math.PI / 4,
    center: [img.width * 0.5, img.height * 0.5]
  }),
  ctx
);
 

transform.js

transform([a,b,c,d,e,f], children...) is a convenience function for advanced developers to add a transform to the current stack. For more information on how the transform operation works, please visit mdn.

let transformOperation = e2d.transform(
  [A, B, C, D, E, F], //{ a: d11, b: d12, c: d21, d: d22, e: d31, f: d32 } for reference
  ...children
);

resetTransform.js and setTransform

These functions give direct access to the transformStack values. To see how these functions work, please see mdn.

let changeCurrentTransform = e2d.setTransform(
  [A, B, C, D, E, F], //{ a: d11, b: d12, c: d21, d: d22, e: d31, f: d32 } for reference
  ...children
);
 
//this is a shortcut for setTransform([1, 0, 0, 1, 0, 0]);
let returnToIdentity = e2d.resetTransform(...children);

shadowStyle.js

Much like lineStyle.js this is a compound property that can be nested.

See mdn for more details.

let shadowStyleDefinition = {
  shadowBlur: 0,
  shadowColor: 'black',
  shadowOffsetX: 0,
  shadowOffsetY: 0
};

Example:

let shadowCommand = e2d.shadowStyle(shadowStyleDefinition,
  //stuff with a shadow
);

stokeArc.js

This function doesn't exist on the Canvas prototype, but was added for completeness. It draws a circular arc.

This command has four forms.

 
let strokeRadius = e2d.strokeArc(radius); //at 0, 0
let strokePosition = e2d.strokeArc(x, y, radius); //full angle
let strokePortion = e2d.strokeArc(x, y, radius, startAngle, endAngle); //specify the angles
let strokeCounterClockwise = e2d.strokeArc(x, y, radius, startAngle, endAngle, true); //counterclockwise

strokeRect.js

This will outline a rectangle. Please visit mdn to see how strokeRect works. It has two forms.

let rect = e2d.strokeRect(width, height); //at 0, 0
let rect2 = e2d.strokeRect(x, y, width, height);

textStyle.js, fillText.js, and strokeText

These functions help you draw text to the screen using Canvas's really poorly implemented text API. Please see mdn for more information about the font properties.

Note: the text function is deprecated.

let style = {
    font: 'Comic Sans MS', //probably pick another font... please?
    textAlign: 'center', // text alignment
    textBaseline: 'top', // base alignment
    direction: 'ltr' // ltr: left to right, rtl: right to left, and inherit
  };
 
let textCommand = e2d.textStyle(style,
  e2d.fillText('hello world!'), //at 0, 0
  e2d.strokeText('other text', x, y), //at x, y
 
  //text, x, y, fill, stroke
  e2d.fillText('some other text too', x, y, maxWidth),
 
  //and maxWidth
  e2d.strokeText('the final example', x, y, maxWidth)
);

transformPoints.js

This utility function transforms a set of points relative to the specified transform matrix. It is used internally by e2d to calculate and apply mouse regions to the canvas.

let matrix = new Float64Array([a, b, c, d, e, f]);
//or...
let matrix = new Float64Array([d11, d12, d21, d22, d31, d32]);
//lookup map
//[d11, d21, d31]  ---- [a, c, e]
//[d12, d22, d32]  ---- [b, d, f]
//[  0,   0,   1]  ---- [0, 0, 1]
 
let points = [
  [x0, y0],
  [x1, y1],
  [x2, y2],
  ...
  [xN, yN]
];
 
let newPoints = transformPoints(points, matrix);

It returns a new array of [x, y] points with the coordinates transformed.

createRegularPolygon.js

Creates a regular polygon shape: an array of arrays.

let radius = 10;
let position = [x, y];
let sides = 6;
let hexagon = e2d.createRegularPolygon(radius, position, sides);
 
console.log(hexagon);
[
  [10, 0],
  [5.000000000000001, 8.660254037844386],
  [-4.999999999999998, 8.660254037844387],
  [-10, 1.2246467991473533e-15],
  [-5.000000000000004, -8.660254037844384],
  [5.000000000000001, -8.660254037844386]
]

moveToLineTo.js

This is a convenience function used with the Array.prototype.map function that maps shapes to drawable polygons.

let hexagonShape = e2d.createRegularPolygon(10, [0, 0], 6);
let hexagonPath = e2d.path( //always wrap drawn paths with e2d.path
  hexagonShape.map(e2d.moveToLineTo) //map each point to an instruction
);
 
e2d.render(
  hexagonPath,
  e2d.stroke(),
  ctx
);
 

License

The MIT License (MIT)

Copyright (c) 2015 Joshua Tenner

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.