我正在尝试创建一个新的画布动画，五个圆围绕一个中心点旋转（类似于太阳系）。所以我创建了五个圆并尝试旋转画布：
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
<script type="text/javascript">
var num=5, balls = [] ;
function Ball() {
this.r = 20;
this.x =Math.random()*200;
this.y = Math.random()*150;
}
function init() {
canvas = document.getElementById("testCanvas");
context = canvas.getContext("2d");
context.clearRect(0,0,context.width,context.height);
context.fillStyle= "lightblue";
context.save();
context.translate(300,300);
for(i=0; i<num ;i++){ balls[i] = new Ball() }
setInterval(draw,50);
}
//function blank() {
//context.fillStyle="white";
//context.fillRect(0,0,context.canvas.width, context.canvas.height);
// }
function draw(){
context.clearRect(0,0,canvas.width,canvas.height);
for(i=0 ; i< num ; i++){
var Ball = balls[i];
context.beginPath();
context.arc(Ball.x, Ball.y, Ball.r,0,2*Math.PI, false);
//context.stroke();
context.fill();
}
context.rotate(0.08);
context.translate(0,0);
context.beginPath();
context.arc(0,0,240,0,Math.PI*2,false);
context.lineWidth = 8;
context.stroke();
}
</script>
</head>
<body onload="init()">
<canvas id="testCanvas" width="600" height="600">
Canvas not supported
</canvas>
</body>
</html>问题是
clearRect调用似乎没有效果；有时我可以从一个或多个圆圈中看到“trails”： 最佳答案
这里有几个问题：
主要原因：在翻译画布时使用clearRect。这意味着它无法清除整个画布。总是清除未翻译的
save（）永远不会被还原（）-它可能是为了以后的翻译
使用requestAnimationFrame来制作动画-这样效率更高。相反，请更改旋转速率。
如果颜色相同，也可以将所有圆弧添加到路径并填充。这将加快绘图速度。
我在下面做了一些修改-
var num = 5,
rotation = 0,
balls = [];
function Ball() {
this.r = 20;
this.x = Math.random() * 200;
this.y = Math.random() * 150;
}
(function init() {
canvas = document.getElementById("testCanvas");
context = canvas.getContext("2d");
context.clearRect(0, 0, context.width, context.height);
context.fillStyle = "lightblue";
for (i = 0; i < num; i++) {
balls[i] = new Ball()
}
requestAnimationFrame(draw);
})();
function draw() {
// reset transforms before clearing
context.setTransform(1, 0, 0, 1, 0, 0);
context.clearRect(0, 0, canvas.width, canvas.height);
// tramslate and rotate an absolute rotation value
context.translate(300, 300);
context.rotate(rotation);
// draw arcs
for (i = 0; i < num; i++) {
var Ball = balls[i];
context.beginPath();
context.arc(Ball.x, Ball.y, Ball.r, 0, 2 * Math.PI, false);
//context.stroke();
context.fill();
}
context.beginPath();
context.arc(0, 0, 240, 0, Math.PI * 2, false);
context.lineWidth = 8;
context.stroke();
// update rotation value and request new frame
rotation += 0.04;
requestAnimationFrame(draw)
}<canvas id="testCanvas" width="600" height="600">
Canvas not supported
</canvas>关于html5 - HTML5 canvas动画和旋转，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/29189891/