HTML5 Canvas Cheatsheet

HTML Canvas

  • HTML5 Canvas Element

    Html5 canvas element

    <canvas id="myCanvas" width="500" height="300">

    Html5 canvas element with fallback content

    <canvas id="myCanvas" width="500" height="300">
  your browser doesn't support canvas!
</canvas>

    2d context

    var context = canvas.getContext('2d');

    Webgl context (3d)

    var context = canvas.getContext('webgl');

  • Shapes

    Draw rectangle

    context.rect(x, y, width, height);
context.fill();
context.stroke();

    Fill rectangle shorthand

    context.fillRect(x, y, width, height);

    Stroke rectangle shorthand

    context.strokeRect(x, y, width, height);

    Draw circle

    context.arc(x, y, radius, 0, Math.PI * 2);
context.fill();
context.stroke();

  • Styles

    Fill

    context.fillStyle = 'red';
context.fill();

    Stroke

    context.strokeStyle = 'red';
context.stroke();

    Linear gradient

    var grd = context.createLinearGradient(x1, y1, x2, y2);
grd.addColorStop(0, 'red');   
grd.addColorStop(1, 'blue');
context.fillStyle = grd;
context.fill();

    Radial gradient

    var grd = context.createRadialGradient(x1, y1, radius1, x2, y2, radius2);
grd.addColorStop(0, 'red');
grd.addColorStop(1, 'blue');
context.fillStyle = grd;
context.fill();

    Pattern

    var imageObj = new Image();
imageObj.onload = function() {
  var pattern = context.createPattern(imageObj, 'repeat');
  context.fillStyle = pattern;
  context.fill();
};
imageObj.src = 'path/to/my/image.jpg';

    Line Join

    context.lineJoin = 'miter|round|bevel';

    Line Cap

    context.lineCap = 'butt|round|square';

    Shadow

    context.shadowColor = 'black';
context.shadowBlur = 20;
context.shadowOffsetX = 10;
context.shadowOffsetY = 10;

    Alpha (Opacity)

    context.globalAlpha = 0.5; // between 0 and 1

  • Color Formats

    String

    context.fillStyle = 'red';

    Hex Long

    context.fillStyle = '#ff0000';

    Hex Short

    context.fillStyle = '#f00';

    RGB

    context.fillStyle = 'rgb(255,0,0)';

    RGBA

    context.fillStyle = 'rgba(255,0,0,1)';

  • Paths

    Begin Path

    context.beginPath();

    Line

    context.lineTo(x, y);

    Arc

    context.arc(x, y, radius, startAngle, endAngle, counterClockwise);

    Quadratic curve

    context.quadraticCurveTo(cx, cy, x, y);

    Bezier curve

    context.bezierCurveTo(cx1, cy1, cx2, cy2, x, y);

    Close Path

    context.closePath();

  • Images

    Draw Image with default size

    var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, x, y);
};
imageObj.src = 'path/to/my/image.jpg';

    Draw image and set size

    var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, x, y, width, height);
};
imageObj.src = 'path/to/my/image.jpg';

    Crop image

    var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, sx, sy, sw, sh, dx, dy, dw, dh);
};
imageObj.src = 'path/to/my/image.jpg';

  • Text

    Fill Text

    context.font = '40px Arial';
context.fillStyle = 'red';
context.fillText('Hello World!', x, y);

    Stroke Text

    context.font = '40pt Arial';
context.strokeStyle = 'red';
context.strokeText('Hello World!', x, y);

    Bold Text

    context.font = 'bold 40px Arial';

    Italic Text

    context.font = 'italic 40px Arial';

    Text Align

    context.textAlign = 'start|end|left|center|right';

    Text Baseline

    context.textBaseline = 'top|hanging|middle|alphabetic|ideographic
|bottom';

    Get Text Width

    var width = context.measureText('Hello world').width;

  • Transforms

    Translate

    context.translate(x, y);

    Scale

    context.scale(x, y);

    Rotate

    context.rotate(radians);

    Flip Horizontally

    context.scale(-1, 1);

    Flip Vertically

    context.scale(1, -1);

    Custom Transform

    context.transform(a, b, c, d ,e, f);

    Set Transform

    context.setTransform(a, b, c, d ,e, f);

    Shear

    context.transform(1, sy, sx, 1, 0, 0);

    Reset

    context.setTransform(1, 0, 0, 1, 0, 0);

  • State Stack

    Push State onto Stack

    context.save();

    Pop State off of Stack

    context.restore();

  • Clipping

    Clip

    // draw path here
context.clip();

  • Image Data

    Get Image Data

    var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;

    Loop Through Image Pixels

    var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;
var len = data.length;
var i, red, green, blue, alpha;

for(i = 0; i < len; i += 4) {
  red = data[i];
  green = data[i + 1];
  blue = data[i + 2];
  alpha = data[i + 3];
}

    Loop Through Image Pixels With Coordinates

    var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;
var x, y, red, green, blue, alpha;

for(y = 0; y < imageHeight; y++) {
  for(x = 0; x < imageWidth; x++) {
    red = data[((imageWidth * y) + x) * 4];
    green = data[((imageWidth * y) + x) * 4 + 1];
    blue = data[((imageWidth * y) + x) * 4 + 2];
    alpha = data[((imageWidth * y) + x) * 4 + 3];
  }
}

    Set Image Data

    context.putImageData(imageData, x, y);

  • Data URLs

    Get Data URL

    var dataURL = canvas.toDataURL();

    Render Canvas with Data URL

    var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, 0, 0);
};

imageObj.src = dataURL;

  • Composites

    Composite Operations

    context.globalCompositeOperation = 'source-atop|source-in|source-out|source-over|destination-atop|destination-in|destination-out|destination-over|lighter|xor|copy';