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AboutAll PostsWarningRandom

Convert an Image to dataUri

  1. function toDataUri(img, scalar = 1) {
  2.   const canvas = document.createElement('canvas');
  3.   canvas.width = img.width * scalar;
  4.   canvas.height = img.height * scalar;
  5.   canvas.getContext('2d').drawImage(img, 0, 0, canvas.width, canvas.height);
  6.   return canvas.toDataURL('image/png');
  7. }
  8.  
  9. const img = new Image();
  10. img.crossOrigin = 'Anonymous';
  11. img.addEventListener('load', () => {
  12.   const thumb = new Image();
  13.   // use the data URI as the source
  14.   thumb.src = toDataUri(img, .3);
  15.   document.body.appendChild(thumb);
  16. });
  17. img.src = 'https://zevanrosser.com/fotoda/slide-shot-9.jpg';

Load an image and convert it to a data URI.

// graphics // javascript // tricks

Make a Debugging Dot

  1. function dot(x, y, radius, color) {
  2.   const el = document.createElement('div');
  3.   const size = `${radius * 2}px`;
  4.   Object.assign(el.style, {
  5.     position: 'absolute', 
  6.     left: `${x}px`,
  7.     top: `${y}px`,
  8.     width: size,
  9.     height: size,
  10.     transform: `translate(${-radius}px, ${-radius}px)`,
  11.     borderRadius: '50%',
  12.     background: color
  13.   });
  14.   el.classList.add('dot');
  15.   document.body.appendChild(el);
  16.   return el;
  17. }
  18.  
  19. dot(100, 100, 10, 'red');
  20. dot(200, 100, 5, 'blue');
  21.  
  22. for (let i = 0; i < 20; i++) {
  23.   dot(20 + i * 12, 200, 5, `hsl(${i * 10}deg, 60%, 50%)`)
  24. }

Draw a dot – good for visualizing things when doing animation and positioning logic.

// css // graphics // javascript // tricks

Draw a Spiral with Resize

  1. const canvas = document.body.appendChild(
  2.   document.createElement('canvas')
  3. );
  4. const c = canvas.getContext('2d');
  5.  
  6. function resize() {
  7.   canvas.width = window.innerWidth;
  8.   canvas.height = window.innerHeight;
  9.   draw();
  10. }
  11.  
  12. function draw() {
  13.   c.clearRect(0, 0, canvas.width, canvas.height);
  14.   c.fillStyle = 'blue';
  15.  
  16.   const iter = 300,
  17.         halfWidth = window.innerWidth / 2,
  18.         halfHeight = window.innerHeight / 2;
  19.   let rad = 0, theta = 0, x, y;
  20.   for (let i = 0; i < iter; i++) {
  21.     x = halfWidth + rad * Math.cos(theta);
  22.     y = halfHeight + rad * Math.sin(theta);
  23.     c.fillRect(x, y, 5, 5);
  24.     rad += Math.min(window.innerWidth, window.innerHeight) * 0.0015;
  25.     theta += .1;
  26.   }
  27. }
  28.  
  29. resize();
  30. window.addEventListener('resize', resize);

Expanding on yesterdays post, this draws a resizable sprial on a canvas.

// canvas // graphics // javascript // math

Easy Canvas Resize

  1. const canvas = document.body.appendChild(
  2.   document.createElement('canvas')
  3. );
  4. const c = canvas.getContext('2d');
  5.  
  6. function resize() {
  7.   canvas.width = window.innerWidth;
  8.   canvas.height = window.innerHeight;
  9.   draw();
  10. }
  11.  
  12. function draw() {
  13.   c.clearRect(0, 0, canvas.width, canvas.height);
  14.   c.fillStyle = 'red';
  15.   // 30% width and height
  16.   c.fillRect(30, 30, 
  17.     window.innerWidth * .3, 
  18.     window.innerHeight * .3);
  19. }
  20.  
  21. resize();
  22. window.addEventListener('resize', resize);

Resizing a canvas is unusual, because setting the width/height of a canvas completely erases it.

If your canvas isn’t animating, you can just redraw after resizing. Depending on what you’re drawing, working in percentages instead of pixel values can make things easier.

If you hit the “Try it out…” button, go into fullscreen and resize your browser window you’ll see things in action.

// canvas // dom // javascript

Semi-golfed Calculator

  1. // "Being clever is not clever"
  2. // -- Bjarne Stroustrup
  3. d = document
  4. b = d.body
  5. a = (e = 'div') => b.appendChild(d.createElement(e))
  6. t = a`input`
  7. s = ''
  8. a()
  9. O = v => t.value = v
  10. '0123456789+-*()/C='.split``.map(v => {
  11.   v == '+' && a()
  12.   _ = a`button`
  13.   _.innerHTML = v
  14.   o = { 
  15.     C(){s = O('')},
  16.     ['='](){O(eval(s))}
  17.   }
  18.   _.onclick = () => o[v] ? o[v]() : (s = s + v, O(s))
  19. })
// dom // golfed // javascript // math // tricks
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