动画中的画布渐变

我遇到了径向渐变渲染的问题;实际上只呈现颜色渐变列表的最后一种颜色。前三圈是动画。渐变和上溯循环之间是否有任何冲突来呈现动画？感谢这是我的代码：动画中的画布渐变

<!doctype html> 

    <html lang="en"> 
    <head> 
    <meta charset="UTF-8"> 
    <title>Disc and Animated-Circle</title> 
    <style> 
     #canvasOne { 
     position: absolute; 
      border: dotted 2px black; 
      left: 50%; 
      margin-left: -450px; 
      top: 50%; 
      margin-top: -250px; 
     } 
    </style> 
    <script type="text/javascript"> 
     window.addEventListener("load", eventWindowLoaded, false); 
     function eventWindowLoaded() { 
     canvasApp(); 
      } 
     function canvasApp() { 
     var theCanvas = document.getElementById("canvasOne"); 
     var context = theCanvas.getContext("2d"); 
       drawScreen(); 
     function drawScreen() { 
     //translation to centre canvas 
     context.setTransform(1, 0, 0, 1, 0, 0); 
     var x = canvasOne.width/2; 
     var y = canvasOne.height/2; 
     var circleWidth = 100; 
     var circleHeight = 100; 
     context.translate(x+.5*circleWidth, y+.5*circleHeight); 
       context.save(); 
      //speed 
     r += speed; 
     //canvas 
     context.fillStyle = "blue"; 
     context.fillRect(-(canvasOne.width/2+circleWidth/2), -(canvasOne.height/2+circleHeight/2), canvasOne.width, canvasOne.height); 
     //circle 1 
     context.strokeStyle = "#66f"; 
     context.lineWidth = 4; 
     context.beginPath(); 
     context.arc(-circleWidth/2, -circleHeight/2, r,(Math.PI/180)*0,(Math.PI/180)*360, false); 
     context.closePath(); 
     //call circle 1 
     context.stroke(); 
     context.restore(); 
     //circle 2 
     context.strokeStyle = "#69f"; 
     context.lineWidth = 4; 
     context.beginPath(); 
     context.arc(-circleWidth/2, -circleHeight/2, r+4,(Math.PI/180)*0,(Math.PI/180)*360, false); 
     context.closePath(); 
     //call circle 2 
     context.stroke(); 
     context.restore(); 
     //circle 3 
     context.strokeStyle = "#6cf"; 
     context.lineWidth = 4; 
     context.beginPath(); 
     context.arc(-circleWidth/2, -circleHeight/2, r+8,(Math.PI/180)*0,(Math.PI/180)*360, false); 
     context.closePath(); 
     //call circle 3 
     context.stroke(); 
     context.restore(); 
     //disc gradient 
     var grad = context.createRadialGradient(100, 100, 0, 100, 100, 100); 
     grad.addColorStop(0, 'white'); 
     grad.addColorStop(.5, 'grey'); 
     grad.addColorStop(1, 'black'); 
     context.fillStyle = grad; 
       //disc 
     context.beginPath(); 
     context.arc(-circleWidth/2, -circleHeight/2, 100, (Math.PI/180)*0,(Math.PI/180)*360, false); 
     context.closePath(); 
     //call disc 
     context.fill(); 
     } //end drawScreen 
    var speed = 20; 
    var r = 100; 
    setInterval(drawScreen, 200); 
    } //end canvasApp 
    </script> 
    </head> 
    <body> 
     <canvas id="canvasOne" width="900" height="500"> 
     Canvas is not supported. 
    </canvas> 
    </body> 
    </html>

来源

2012-08-17 user1607274

你有梯度的，在（100,100）的中心，这是不是圆的中心。

行

var grad = context.createRadialGradient(100, 100, 0, 100, 100, 100);

更改为

var grad = context.createRadialGradient(-circleWidth/2, -circleHeight/2, 0, -circleWidth/2, -circleHeight/2, 100);

来源

2012-08-19 07:35:51 jing3142

感谢京3142，现在它的工作原理。 – user1607274 2012-08-21 08:04:33

动画中的画布渐变

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