微信小程序 二维码canvas绘制实例详解

var canvas = {  width: 100,  height:36};function verification(ctx) {  // //清空画布  ctx.clearRect(0, 0, canvas.width, canvas.height);  // //生成随机颜色  function getRandomColor() {    return "#" + ("00000" + ((Math.random() * 16777215 + 0.5) >> 0).toString(16)).slice(-6);  }  // //定义线性渐变  var gradient = ctx.createLinearGradient(0, 0, canvas.width, canvas.height);  gradient.addColorStop("0", getRandomColor());  gradient.addColorStop("0.5", getRandomColor());  gradient.addColorStop("1.0", getRandomColor());  // //生成随机数  function rnd(min, max) {    return min + Math.floor(Math.random() * (max - min + 1));  }  // //绘制干扰线条  function line() {    ctx.beginPath();    ctx.moveTo(rnd(0, canvas.width), rnd(0, canvas.height));    ctx.lineTo(rnd(0, canvas.width), rnd(0, canvas.height));    ctx.closePath();    ctx.lineWidth = rnd(1, 3);    ctx.setFillStyle(gradient)    ctx.stroke();  }  // //绘制干扰点  function point() {    ctx.fillRect(rnd(0, canvas.width), rnd(0, canvas.height), 2, 2);  }  // //绘制验证码  var text = rnd(1000, 9999);  ctx.setFontSize(30)  ctx.setFillStyle(gradient)  ctx.fillText(text,2, 25);  // //生成干扰元素  for (var i = 0; i < 8; i++) {    line();  }  for (var i = 0; i <100; i++) {    point();  }  ctx.draw()  return text;}module.exports = { verification: verification };