详解如何用HTML5 Canvas API控制图片的缩放变换

缩放变换scale(sx,sy)传入两个参数，分别是水平方向和垂直方向上对象的缩放倍数。例如context.scale(2,2)就是对图像放大两倍。其实，看上去简单，实际用起来还是有一些问题的。我们来看一段代码：

JavaScript Code复制内容到剪贴板

<!DOCTYPE html> <html lang="zh">
<head> <meta charset="UTF-8">
<title>缩放变换</title> <style>
body { background: url("./images/bg3.jpg") repeat; } #canvas { border: 1px solid #aaaaaa; display: block; margin: 50px auto; }
</style> </head>
<body> <div id="canvas-warp">
<canvas id="canvas"> 你的浏览器居然不支持Canvas？！赶快换一个吧！！
</canvas> </div>
<script>
window.onload = function(){ var canvas = document.getElementById("canvas");
canvas.width = 800; canvas.height = 600;
var context = canvas.getContext("2d"); context.fillStyle = "#FFF";
context.fillRect(0,0,800,600);
context.strokeStyle = "red"; context.lineWidth = 5;
for(var i = 1; i < 4; i++){ context.save();
context.scale(i,i); context.strokeRect(50,50,150,100);
context.restore(); }
}; </script>
</body> </html>