让图片旋转任意角度及JQuery插件使用介绍

jQuery.fn.rotate = function(angle,whence) { 
var p = this.get(0); 
// we store the angle inside the image tag for persistence 
if (!whence) { 
p.angle = ((p.angle==undefined?0:p.angle) + angle) % 360; 
} else { 
p.angle = angle; 
} 
if (p.angle >= 0) { 
var rotation = Math.PI * p.angle / 180; 
} else { 
var rotation = Math.PI * (360+p.angle) / 180; 
} 
var costheta = Math.round(Math.cos(rotation) * 1000) / 1000; 
var sintheta = Math.round(Math.sin(rotation) * 1000) / 1000; 
//alert(costheta+","+sintheta); 
if (document.all && !window.opera) { 
var canvas = document.createElement('img'); 
canvas.src = p.src; 
canvas.height = p.height; 
canvas.width = p.width; 
canvas.style.filter = "progid:DXImageTransform.Microsoft.Matrix(M11="+costheta+",M12="+(-sintheta)+",M21="+sintheta+",M22="+costheta+",SizingMethod='auto expand')"; 
} else { 
var canvas = document.createElement('canvas'); 
if (!p.oImage) { 
canvas.oImage = new Image(); 
canvas.oImage.src = p.src; 
} else { 
canvas.oImage = p.oImage; 
} 
canvas.style.width = canvas.width = Math.abs(costheta*canvas.oImage.width) + Math.abs(sintheta*canvas.oImage.height); 
canvas.style.height = canvas.height = Math.abs(costheta*canvas.oImage.height) + Math.abs(sintheta*canvas.oImage.width); 
var context = canvas.getContext('2d'); 
context.save(); 
if (rotation <= Math.PI/2) { 
context.translate(sintheta*canvas.oImage.height,0); 
} else if (rotation <= Math.PI) { 
context.translate(canvas.width,-costheta*canvas.oImage.height); 
} else if (rotation <= 1.5*Math.PI) { 
context.translate(-costheta*canvas.oImage.width,canvas.height); 
} else { 
context.translate(0,-sintheta*canvas.oImage.width); 
} 
context.rotate(rotation); 
context.drawImage(canvas.oImage, 0, 0, canvas.oImage.width, canvas.oImage.height); 
context.restore(); 
} 
canvas.id = p.id; 
canvas.angle = p.angle; 
p.parentNode.replaceChild(canvas, p); 
} 
jQuery.fn.rotateRight = function(angle) { 
this.rotate(angle==undefined?90:angle); 
} 
jQuery.fn.rotateLeft = function(angle) { 
this.rotate(angle==undefined?-90:-angle); 
}