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javascript异步编程----用jscex画圆

2011-08-16

今天来画圆吧! 在支持html5的浏览器中执行下面代码:<!DOCTYPE HTML><html><body><canvas id="myCanvas" width="480" height="300" style="border:1px solid #c3c3c3;">Your browser does not supp...

今天来画圆吧!

在支持html5的浏览器中执行下面代码:

<!DOCTYPE HTML>
<html>
<body>

<canvas id="myCanvas" width="480" height="300" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script type="text/javascript">

var c = document.getElementById("myCanvas");
var cxt = c.getContext("2d");
var x = 150;
var y = 150;
var r = 100;
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y + tempY);
}
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y - tempY);
}
cxt.stroke();

</script>

</body>
</html>
在Canvas里显示如下:

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但是,我们明明是在画圆,怎么没有看到画圆的过程?javascript就是这样,解释完就画完了,而不会呈现解释的过程,这也是为什么javascript不用考虑多线程问题,仅仅UI线程。那么怎么看到画圆的过程?

jscex闪亮登场!

<!DOCTYPE HTML>
<html>
<body>
<canvas id="myCanvas" width="480" height="300" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script language="javascript" type="text/javascript" src="lib/uglifyjs-parser.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.builderBase.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.async.js"></script>
<script type="text/javascript">
var c = document.getElementById("myCanvas");
var cxt = c.getContext("2d");
var x = 150;
var y = 150;
var r = 100;
var drawAsync = eval(Jscex.compile("async", function () {
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
$await(Jscex.Async.sleep(10));
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y + tempY);
cxt.stroke();
}
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
$await(Jscex.Async.sleep(10));
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y - tempY);
cxt.stroke();
}

}));
drawAsync().start();
</script>

</body>
</html>

这样就可以目睹画圆全过程!

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