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canvas.md

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Canvas
JavaScript
2017/sheet

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()
c.restore()

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

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.createLinearGradient(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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