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; 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>
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：
