绘制一个矩形。使用渐变笔触 - 在线编辑器

          <canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
您的浏览器不支持 HTML5 canvas 标签。</canvas>
<script>
  var c = document.getElementById("myCanvas");
  var ctx = c.getContext("2d");
  var gradient = ctx.createLinearGradient(0, 0, 170, 0);
  gradient.addColorStop("0", "magenta");
  gradient.addColorStop("0.5", "blue");
  gradient.addColorStop("1.0", "red");
  //渐变填
  ctx.strokeStyle = gradient;
  ctx.lineWidth = 5;
  ctx.strokeRect(20, 20, 150, 100);
</script>
        