网站二维码海报

生成一张带有网站标题、简介和二维码的海报，并下载。方便进行分享。
// ==UserScript==
// @name        网站二维码海报
// @namespace   QRCode post for website
// @description 生成一张带有网站标题、简介和二维码的海报，并下载。方便进行分享。
// @match       *://*/*
// @grant       GM_download
// @grant       GM_registerMenuCommand
// @require     https://cdnjs.cloudflare.com/ajax/libs/qrcodejs/1.0.0/qrcode.min.js
// @noframes
// @version     0.0.2
// @author      -
// @description 2020/5/9 下午8:59:19
// ==/UserScript==

const makerQRCode = ()=>{
  const qrcodepostmaker = document.createElement('div');
  qrcodepostmaker.id = 'qrcodepostmaker';
  qrcodepostmaker.style.display = 'none';
  document.body.appendChild(qrcodepostmaker);

  const textComputer = (text, style, width, ctx) => {
    if(text.replace(/\s/g, '').length === 0) { return [] }
    ctx.font = style;
    let temp = 0;
    const row = [];
    for (let i = 0; i <= text.length; i++) {
      if (ctx.measureText(text.substring(temp, i)).width >= width) {
        row.push(text.substring(temp, i-1));
        temp = i-1;
      }else if(i === text.length){
        row.push(text.substring(temp, i));
      }
    }
    return row;
  };
  const textWriter = (
    textArr,
    Style,
    align,
    color,
    borderColor,
    fontSize,
    lineHeight,
    pos,
    ctx
  ) => {
    ctx.font = Style;
    ctx.textAlign = align;
    ctx.fillStyle = color;
    ctx.strokeStyle = borderColor;
    for (const text of textArr) {
      pos.y += fontSize * lineHeight;
      // ctx.strokeText(text, pos.x, pos.y);
      ctx.fillText(text, pos.x, pos.y);
    }
    return pos;
  };

  const makerQRPost = () => {
    const canvas = document.querySelector('#qrcodepostmaker > canvas');
    const ctx = canvas.getContext('2d');
    const QRCodeData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const title = document.title;
    const desc = document.head.querySelector('meta[name="description"]') ? document.head.querySelector('meta[name="description"]').content : '';
    const cardWidth = 360;
    const lineHeight = 1.6;
    const margin = 36;
    const titleStyle = 'Bold 18px "Microsoft YaHei"';
    const descStyle = '16px "Microsoft YaHei"';
    const titleArray = textComputer(
      title,
      titleStyle,
      cardWidth - margin * 2,
      ctx
    );
    const descArray = textComputer(desc, descStyle, cardWidth - margin * 2, ctx);
    const cardHeight = margin * 2.5
      + 18 * titleArray.length * lineHeight
      + 16 * descArray.length * lineHeight
      + (descArray.length ? margin/2 : 0)
      + 300;
    canvas.width = cardWidth;
    canvas.height = cardHeight;
    const myGradient = ctx.createLinearGradient(0, 0, 0, cardHeight);
    myGradient.addColorStop(0, "#2980B9");
    myGradient.addColorStop(0.5, "#6DD5FA");
    myGradient.addColorStop(1, "#FFFFFF");
    ctx.fillStyle = myGradient;
    ctx.fillRect(0, 0, cardWidth, cardHeight);
    ctx.fillStyle = "#FFFFFF";
    ctx.beginPath();
    ctx.arc(margin*0.4, cardHeight - margin*5, margin, 0, Math.PI*2, true);
    ctx.arc(cardWidth-margin*0.4, cardHeight - margin*3, margin*0.8, 0, Math.PI*2, true);
    ctx.fillRect(0, cardHeight - margin*5, cardWidth/2, margin*5);
    ctx.fillRect(cardWidth/2, cardHeight - margin*3, cardWidth/2, margin*3);
    ctx.fill();
    const titleEnd = textWriter(
      titleArray,
      titleStyle,
      'center',
      'black',
      'rgba(255, 255, 255, 0.6)',
      18,
      lineHeight,
      { x: cardWidth / 2, y: margin },
      ctx
    );
    const descEnd = textWriter(
      descArray,
      descStyle,
      'left',
      'black',
      'rgba(255, 255, 255, 0.6)',
      16,
      lineHeight,
      { x: margin, y: titleEnd.y+margin/2 },
      ctx
    );
    ctx.fillStyle = 'white';
    ctx.fillRect((cardWidth-288)/2, descEnd.y + margin - 24, 288, 288);
    ctx.putImageData(QRCodeData, (cardWidth-256)/2, descEnd.y + margin);
    textWriter(
      ['（长按识别二维码进行访问）'],
      descStyle,
      'center',
      'rgba(0, 0, 0, 0.6)',
      'rgba(255, 255, 255, 0.6)',
      16,
      lineHeight,
      { x: cardWidth / 2, y: descEnd.y + margin + 256 },
      ctx
    );
    GM_download(canvas.toDataURL("image/png"), title+'.png')
    qrcodepostmaker.parentNode.removeChild(qrcodepostmaker)
  };

  let tryTimes = 30;
  const makeQRCode = window.setInterval(() => {
    try {
      new QRCode(
        document.getElementById('qrcodepostmaker'),
        window.location.href
      );
      window.clearInterval(makeQRCode);
      makerQRPost();
    } catch (error) {
      console.log(error)
      tryTimes--;
      if (!tryTimes) {
        window.clearInterval(makeQRCode);
        alert('没能成功载入功能库，请刷新重试~');
      }
    }
  }, 200);
}
GM_registerMenuCommand('生成二维码海报', makerQRCode)