html5 canvas 缩放为什么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

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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> </head> <style type="text/css"> body{margin:20px auto; padding:0; width: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>
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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：