141 lines
2.2 KiB
Markdown
141 lines
2.2 KiB
Markdown
---
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title: Canvas
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category: JavaScript
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---
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### Getting the context
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```js
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var canvas = document.getElementById('c')
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var c = canvas.getContext('2d')
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```
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### Basic drawing
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```js
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// x = 10, y = 20, width = 200, height = 100
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c.fillStyle = '#ff0000'
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c.strokeStyle = '#ff00ff'
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```
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```js
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c.lineWidth = 5
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c.lineCap = 'round'
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```
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```js
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c.fillRect(10, 20, 200, 100)
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```
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```js
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c.stroke()
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c.fill()
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```
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### Saving and restoring
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```js
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c.save()
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```
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```js
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c.restore()
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```
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Saves: `strokeStyle` `fillStyle` `globalAlpha` `lineWidth` `lineCap` `lineJoin` `miterLimit` `shadowOffsetX` `shadowOffsetY` `shadowBlur` `shadowColor`
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`globalCompositeOperation`, Transformations (`translate` `rotate` `scale` `transform` `setTransform`), Clipping path
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### Animation
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```js
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onframe: function() {
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c.clearRect(0, 0, w, h)
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}
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```
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### Transformations
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```js
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c.translate(0, 0)
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c.rotate(Math.PI*2/5)
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c.scale(1.0, 1.0)
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```
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To rotate along origin:
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```js
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c.translate(ox, oy)
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c.rotate(theta)
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c.translate(-ox, -oy)
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```
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To scale along origin:
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```js
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c.translate(-ox*x, -oy*y)
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c.scale(x, y)
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c.translate(ox/x, oy/y)
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```
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See [MDN: Transformations][xform].
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### Image drawing
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```js
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c.drawImage(image, dx, dy, [dw, dh]);
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/* `image` can be HTML Image/Canvas/Video */
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```
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See [MDN: Images][images].
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### Colors, styles shadows
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```js
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c.strokeStyle = '#ff00ff';
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c.fillStyle = '#ff00ff';
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```
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```js
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c.shadowOffsetX = 0;
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c.shadowOffsetY = 0;
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c.shadowOffsetBlur = 3.0;
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c.shadowColor = 'rgba(0,0,0,0.2)';
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```
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See [MDN: Styles][styles]
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### Gradients
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```js
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gr = c.createLinearGradient(x0,y0,x1,y1)
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gr = c.createRadialGradient(x0,y0,r0,x1,y1,r1)
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pat = c.createPattern(image, 'repeat-x')
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```
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```js
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c.fillStyle = gr
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```
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### Drawing
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```js
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c.beginPath()
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c.moveTo(x,y)
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c.lineTo(x,y)
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c.quadraticCurveTo(cpx,cpy,x,y)
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c.bezierCurveTo(cp1x,cp1y,cp2x,cp2y)
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c.arcTo(...)
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c.arc(...)
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c.closePath()
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```
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### More resources
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* [Canvas Cheatsheet PDF][pdf]
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[pdf]: http://www.nihilogic.dk/labs/canvas_sheet/HTML5_Canvas_Cheat_Sheet.pdf
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[xform]: https://developer.mozilla.org/en-US/docs/Canvas_tutorial/Transformations
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[styles]: https://developer.mozilla.org/en-US/docs/Canvas_tutorial/Applying_styles_and_colors
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[images]: https://developer.mozilla.org/en-US/docs/Canvas_tutorial/Using_images
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