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canvas.md

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Canvas
JavaScript

Getting the context

var canvas = document.getElementById('c');
var c = canvas.getContext("2d");

Basic drawing

// x = 10, y = 20, width = 200, height = 100
c.fillStyle = '#ff0000';
c.strokeStyle = '#ff00ff';

c.lineWidth = 5;
c.lineCap = 'round';

c.fillRect(10, 20, 200, 100);

c.stroke();
c.fill();

Saving and restoring

c.save();

// Saves:
// strokeStyle fillStyle globalAlpha lineWidth lineCap lineJoin miterLimit 
// shadowOffsetX shadowOffsetY shadowBlur shadowColor
// globalCompositeOperation
// Transformations: translate rotate scale transform setTransform
// Clipping path

c.restore();

Animation

onframe: function() {
  c.clearRect(0, 0, w, h);
}

Transformations

c.translate(0, 0)
c.rotate(Math.PI*2/5)
c.scale(1.0, 1.0)

To rotate along origin:

c.translate(ox, oy)
c.rotate(theta)
c.translate(-ox, -oy)

To scale along origin:

c.translate(-ox*x, -oy*y)
c.scale(x, y)
c.translate(ox/x, oy/y)

See MDN: Transformations.

Image drawing

c.drawImage(image, dx, dy, [dw, dh]);
/* `image` can be HTML Image/Canvas/Video */

See MDN: Images.

Colors, styles shadows

c.strokeStyle = '#ff00ff';
c.fillStyle = '#ff00ff';

c.shadowOffsetX = 0;
c.shadowOffsetY = 0;
c.shadowOffsetBlur = 3.0;
c.shadowColor = 'rgba(0,0,0,0.2)';

See MDN: Styles.

Gradients

gr = c.createLinearGgadient(x0,y0,x1,y1)
gr = c.createRadialGradient(x0,y0,r0,x1,y1,r1)
pat = c.createPattern(image, 'repeat-x')

c.fillStyle = gr

Drawing

c.beginPath()
c.moveTo(x,y)
c.lineTo(x,y)
c.quadraticCurveTo(cpx,cpy,x,y)
c.bezierCurveTo(cp1x,cp1y,cp2x,cp2y)
c.arcTo(...)
c.arc(...)
c.closePath()

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