js 旋转图片

/*图片转动函数*/
function rotate(o, p) {
var img = document.getElementById(o);
if(!img || !p) return false;
var n = img.getAttribute('step');
if(n == null) n=0;
if(p=='right') {
(n==3)?n=0:n++;
}
else if(p="left"){
(n==0)?n=3:n--;
}
img.setAttribute('step', n);

if(document.all) {
img.style.filter = "progid:DXImageTransform.Microsoft.BasicImage(rotation="+ n +")";

switch(n){
case 0:
img.parentNode.style.height = img.height;
break;
case 1:
img.parentNode.style.height = img.width;
break;
case 2:
img.parentNode.style.height = img.height;
break;
case 3:
img.parentNode.style.height = img.width;
break;
}
}
else{
var c = document.getElementById('canvas_'+o);
if(c==null){
img.style.visibility = 'hidden';
img.style.position = 'absolute';
c = document.createElement('canvas');
c.setAttribute('id', 'canvas_'+o);
img.parentNode.appendChild(c);
}
var canvasContext = c.getContext('2d');
canvasContext.save();
switch(n){
default :
case 0:
c.setAttribute('width', img.width);
c.setAttribute('height', img.height);
canvasContext.rotate(0 * Math.PI/180);
canvasContext.drawImage(img, 0, 0);
break;
case 1:
c.setAttribute('width', img.height);
c.setAttribute('height', img.width);
canvasContext.rotate(90 * Math.PI/180);
canvasContext.drawImage(img, 0, -img.height);

break;
case 2:
c.setAttribute('width', img.width);
c.setAttribute('height', img.height);
canvasContext.rotate(180 * Math.PI/180);
canvasContext.drawImage(img, -img.width, -img.height);
break;
case 3:
c.setAttribute('width', img.height);
c.setAttribute('height', img.width);
canvasContext.rotate(270 * Math.PI/180);
canvasContext.drawImage(img, -img.width, 0);
break;

}
canvasContext.restore();
}

}