Transform变形方法的可视化演示

canvas 的变形方法transform是三个基本变形方法的结合，他们是 translate——移动；rotate ——旋转，在transform中分解为x，y两个方向的斜切；和scale——缩放。他的参数是变形矩阵的六个数值：m11, m12, m21, m22, dx, dy 变形矩阵：
m11 m21 dx m12 m22 dy 0 0 1 对于transform方法的使用，其实很难把握，所以写了下面这个演示
<!doctype html>
<html>
<head>
<meta charset='UTF-8' />
<title>cssass.com</title>
<style>
#rule,#pad{float:left;margin:10px;}
#rule p{padding;0;margin:0;line-height:25px;}
#rule label{display:inline-block;width:80px;text-align:right;font-size:12px;}
#rule input{border:0;width:40px;}
#rule b{position:relative;display:inline-block;width:150px;height:10px;font-size:0;line-height:0;background:#fff;border:1px solid #aaa;border-radius:4px;-moz-border-radius:4px;-webkit-border-radius:4px;}
#rule p a{position:absolute;top:-4px;left:50%;width:15px;height:15px;margin-left:-8px;border:1px solid #d3d3d3;background:#ececec;border-radius:4px;-moz-border-radius:4px;-webkit-border-radius:4px;}
#rule p a:hover{border:1px solid #999;background:#dcdcdc;}
.footer{font-size:12px;padding:10px 0;}
</style>
</head>
<body>
<div id='rule'>
	<h3>Transform方法可视化操作演示</h3>
	<p onmousedown='G.change(this,event,4);'><label>水平缩放 m11: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='m11' type='text' /></p>
	<p onmousedown='G.change(this,event,4);'><label>y轴斜切 m12: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='m12' type='text' /></p>
	<p onmousedown='G.change(this,event,4);'><label>x轴斜切 m21: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='m21' type='text' /></p>
	<p onmousedown='G.change(this,event,4);'><label>垂直缩放 m22: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='m22' type='text' /></p>
	<p onmousedown='G.change(this,event,1000);'><label>平移 dx: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='dx' type='text' /></p>
	<p onmousedown='G.change(this,event,1000);'><label>纵移 dy: </label> <b class='range'><a onfocus="blur();"  href='javascript:;'>&nbsp;</a></b> <input id='dy' type='text' /></p>
	<div class='footer'>首先在右侧用鼠标画一矩形。<br />Javascript by <a href='http://www.cssass.com'>cssass.com</a></div>
</div>
<canvas id="pad" width='800' height="600" style="position:relative;border:1px solid #c3c3c3;cursor:crosshair;">注意：ie9以下用户请绕行</canvas>
<script>
var $id=function(o){return document.getElementById(o);}
var con=$id("pad").getContext('2d');
var G={};
G.x1=G.y1=G.x2=G.y2=0;
G.val=[[4,1],[4,0],[4,0],[4,1],[1000,0],[1000,0]];
G.init=function(){
	var list=$id('rule').getElementsByTagName('p');
	var left, value;
	for(var i=0; i<list.length; i++){
		value = G.val[i][1];
		left =(0.5 + G.val[i][1] / G.val[i][0] ) * 100;
		list[i].getElementsByTagName('a')[0].style.left= left + '%';
		list[i].getElementsByTagName('input')[0].value= value;
	}
}
G.draw=function(){
	G.init();
	var e = arguments[0];
		G.x1 = (e.layerX) ? e.layerX : e.offsetX,
		G.y1 = (e.layerY) ? e.layerY : e.offsetY,
	$id("pad").onmousemove=function(e){
		con.clearRect(0,0,800,600);
		G.x2= (e.layerX) ? e.layerX : e.offsetX;
		G.y2= (e.layerY) ? e.layerY : e.offsetY;
		con.save();
		con.translate(G.x1,G.y1)
		G.rect(G.x1,G.y1,G.x2,G.y2);
		con.restore();
	}
	$id("pad").onmouseup=function(){
		$id("pad").onmousedown=null;
		$id("pad").onmousemove=null;
	}
}
G.change=function(obj,e,l,v){
	var o=obj.getElementsByTagName('a')[0];
	var e = e ? e : window.event;
	if(!window.event) {e.preventDefault();}
	var tX=o.offsetLeft,
		dx=e.clientX;
	document.onmousemove=function(e){
		var e = e ? e : window.event;
		var len=tX+e.clientX-dx+8;
		if(len>=0 && len<=150){
			var rat=(len / 150) * 100;
			o.style.left=rat+ "%";
			obj.getElementsByTagName('input')[0].value =l * Math.round((rat - 50)*10)/1000;
			G.transform();
		}
		if(window.event) e.returnValue=false;
	}
	document.onmouseup=function(){
		document.onmousemove=null;
		document.onmouseup=null;
	}
}
G.transform=function(){
	var m11=($id('m11').value == 0)? 0.001 : $id('m11').value,  //firefox下m11,m12值不能为0
		m12=$id('m12').value,
		m21=$id('m21').value,
		m22=($id('m22').value == 0)? 0.001 : $id('m22').value,
		dx=$id('dx').value,
		dy=$id('dy').value;
	con.clearRect(0,0,800,600);
	con.save();
	con.translate(G.x1,G.y1);  //变形的参考点设为图形的左上角
	con.transform(m11, m12, m21, m22, dx, dy);
	G.rect(G.x1,G.y1,G.x2,G.y2);
	con.restore();
}
G.rect=function(x1,y1,x2,y2){
	var grd=con.createLinearGradient(0, 0, x2 - x1, y2 - y1); //弄一个渐变效果
			grd.addColorStop(0,"#3F5816");
			grd.addColorStop(1,"#B40000");
		con.fillStyle=grd;
		con.fillRect(0, 0, x2 - x1, y2 - y1);
}
window.addEventListener("load", G.init, false);
$id("pad").addEventListener("mousedown", G.draw, false);
</script>
</body>
</html>