有些人有些不解，为什么Canvas的坐标是从左上角开始的，而且向下是Y的正方向，向右是X的正方向？其实我也很不理解~~
为什么就不能给我们更多的自定义功能呢？下面我改写了一段Canvas画布调整的代码，包含了Canvas画布的移动、缩放和旋转等相关功能
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<style type="text/css">
body{margin:20px auto; padding:0; 1000px }
canvas{border:dashed 2px #ccc}
span{font-size:16px; cursor:pointer}
</style>
<script type="text/javascript">
function $$(id){
return document.getElementById(id);
}
function drawRect(co){
var can = $$('can');
cans = can.getContext('2d');
cans.strokeStyle = co;
cans.lineWidth = 3;
cans.strokeRect(600,50,80,40);
}
function drawCircle(co){
cans.beginPath();
cans.arc(30,30,30,0,Math.PI*2,1);
cans.closePath();
cans.strokeStyle = co;
cans.lineWidth = 3;
cans.stroke();
}
function mv_click(){
var can = $$('can');
var cans = can.getContext('2d');
cans.translate(40,40);
drawRect('black');
}
function zoom_click(){
var can = $$('can');
var cans = can.getContext('2d');
drawCircle('red');
cans.scale(0.5,1.5);
drawCircle('green');
}
function rotate_click(){
var can = $$('can');
var cans = can.getContext('2d');
cans.rotate(Math.PI*2/360*45);
drawRect('green');
cans.rotate(-Math.PI/4);
drawRect('black');
}
</script>
<body onload="drawRect('red');">
<canvas id="can" width="1000px" height="800px"></canvas>
<span onclick="mv_click();"><mark>移动</mark></span>
<span onclick="zoom_click();"><mark>缩放</mark></span>
<span onclick="rotate_click();"><mark>旋转</mark></span>
</body>
</html>
注意：调整了画布后，以后的操作就按照调整后的，千万注意坐标哦
移动功能：
缩放功能：
旋转功能：
