discourse/app/assets/javascripts/wizard/lib/preview.js.es6

/*eslint no-bitwise:0 */

export const LOREM = `
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Nullam eget sem non elit tincidunt rhoncus. Fusce velit nisl,
porttitor sed nisl ac, consectetur interdum metus. Fusce in
consequat augue, vel facilisis felis. Nunc tellus elit, and
semper vitae orci nec, blandit pharetra enim. Aenean a ebus
posuere nunc. Maecenas ultrices viverra enim ac commodo
Vestibulum nec quam sit amet libero ultricies sollicitudin.
Nulla quis scelerisque sem, eget volutpat velit. Fusce eget
accumsan sapien, nec feugiat quam. Quisque non risus.
placerat lacus vitae, lacinia nisi. Sed metus arcu, iaculis
sit amet cursus nec, sodales at eros.`;

export function createPreviewComponent(width, height, obj) {
  return Ember.Component.extend({
    layoutName: 'components/theme-preview',
    width,
    height,
    ctx: null,
    loaded: false,

    didInsertElement() {
      this._super();
      const c = this.$('canvas')[0];
      this.ctx = c.getContext("2d");
      this.reload();
    },

    reload() {
      this.load().then(() => {
        this.loaded = true;
        this.triggerRepaint();
      });
    },

    triggerRepaint() {
      Ember.run.scheduleOnce('afterRender', this, 'repaint');
    },

    repaint() {
      if (!this.loaded) { return false; }

      const colors = this.get('wizard').getCurrentColors();
      if (!colors) { return; }

      const { ctx } = this;

      ctx.fillStyle = colors.secondary;
      ctx.fillRect(0, 0, width, height);

      this.paint(ctx, colors, this.width, this.height);

      // draw border
      ctx.beginPath();
      ctx.strokeStyle='rgba(0, 0, 0, 0.2)';
      ctx.rect(0, 0, width, height);
      ctx.stroke();
    }
  }, obj);
}

export function loadImage(src) {
  const img = new Image();
  img.src = src;

  return new Ember.RSVP.Promise(resolve => img.onload = () => resolve(img));
};

export function parseColor(color) {
  const m = color.match(/^#([0-9a-f]{6})$/i);
  if (m) {
    const c = m[1];
    return [ parseInt(c.substr(0,2),16), parseInt(c.substr(2,2),16), parseInt(c.substr(4,2),16) ];
  }

  return [0, 0, 0];
}

export function brightness(color) {
  return (color[0] * 0.299) + (color[1] * 0.587) + (color[2] * 0.114);
}

function rgbToHsl(r, g, b) {
  r /= 255;
  g /= 255;
  b /= 255;
  let max = Math.max(r, g, b), min = Math.min(r, g, b);
  let h, s, l = (max + min) / 2;

  if (max === min) {
    h = s = 0;
  } else {
    const d = max - min;
    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
    switch(max){
      case r: h = (g - b) / d + (g < b ? 6 : 0); break;
      case g: h = (b - r) / d + 2; break;
      case b: h = (r - g) / d + 4; break;
    }
    h /= 6;
  }

  return [h, s, l];
}

function hue2rgb(p, q, t) {
  if (t < 0) { t += 1; }
  if (t > 1) { t -= 1; }
  if (t < 1/6) { return p + (q - p) * 6 * t; }
  if (t < 1/2) { return q; }
  if (t < 2/3) { return p + (q - p) * (2/3 - t) * 6; }
  return p;
}

function hslToRgb(h, s, l) {
  let r, g, b;

  if (s === 0) {
    r = g = b = l; // achromatic
  } else {
    const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
    const p = 2 * l - q;
    r = hue2rgb(p, q, h + 1/3);
    g = hue2rgb(p, q, h);
    b = hue2rgb(p, q, h - 1/3);
  }

  return [r * 255, g * 255, b * 255];
}

export function lighten(color, percent) {
  const hsl = rgbToHsl(color[0], color[1], color[2]);
  const scale = percent / 100.0;
  const diff = scale > 0 ? 1.0 - hsl[2] : hsl[2];

  hsl[2] = hsl[2] + diff * scale;
  color = hslToRgb(hsl[0], hsl[1], hsl[2]);

  return '#' +
    ((0|(1<<8) + color[0]).toString(16)).substr(1) +
    ((0|(1<<8) + color[1]).toString(16)).substr(1) +
    ((0|(1<<8) + color[2]).toString(16)).substr(1);
}

export function chooseBrighter(primary, secondary) {
  const primaryCol = parseColor(primary);
  const secondaryCol = parseColor(secondary);
  return brightness(primaryCol) < brightness(secondaryCol) ? secondary : primary;
}

export function darkLightDiff(adjusted, comparison, lightness, darkness) {
  const adjustedCol = parseColor(adjusted);
  const comparisonCol = parseColor(comparison);
  return lighten(adjustedCol, (brightness(adjustedCol) < brightness(comparisonCol)) ?
                               lightness : darkness);
}


export function drawHeader(ctx, colors, width, height) {
  ctx.save();
  ctx.beginPath();
  ctx.rect(0, 0, width, height);
  ctx.fillStyle = colors.header_background;
  ctx.shadowColor = "rgba(0, 0, 0, 0.25)";
  ctx.shadowBlur = 2;
  ctx.shadowOffsetX = 0;
  ctx.shadowOffsetY = 2;
  ctx.fill();
  ctx.restore();
}