HTML5 canvas如何绘制动态径向渐变(2)-木庄网络博客

使用Web浏览器显示上述HTML文件。将显示如下所示的效果。

2345截图20181203142011.png

如果在蓝色画布中移动鼠标，渐变将会随着变化。

HTML5 canvas

在渐变开始和渐变结束的圆心不一致的情况下

代码如下

<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title></title>
  <meta charset="utf-8" />
  <style>
    body {
      background: #C0C0C0;
    }  
</style>
  <script>
    function PageLoad() {
      var CanvasWidth = 1200;      
      var CanvasHeight = 480;      
      var canvas = document.getElementsByTagName('canvas')[0],
          ctx = null,
          grad = null,
          color = 255;      
      if (canvas.getContext('2d')) {
        ctx = canvas.getContext('2d');
        ctx.clearRect(0, 0, CanvasWidth, CanvasHeight);
 
        grad = ctx.createRadialGradient(0, 0, 64, 128, 64, 320);
        grad.addColorStop(0, '#b43700');
        grad.addColorStop(1, '#ffe063');
        ctx.fillStyle = grad;
 
        ctx.fillRect(0, 0, CanvasWidth, CanvasHeight);
 
        canvas.addEventListener('mousemove', function (evt) {
                var width = window.innerWidth,
          height = window.innerHeight,
          x = event.clientX,
          y = event.clientY,
 
          grad = ctx.createRadialGradient(x, y, 64, x+128, y+64, 320);
          grad.addColorStop(0, '#b43700');
          grad.addColorStop(1, '#ffe063');
 
          ctx.fillStyle = grad;
          ctx.fillRect(0, 0, CanvasWidth, CanvasHeight);
        }, false);
      }
    }  
</script>
</head>
<body onload="PageLoad();">
  <canvas width="1200" height="480"></canvas>
</body>
</html>