关于自由拖拽完成的剪切区域（UI组件之图片剪切器）

var x, y,areaWidth,areaHeight;

    var down;//闪光的判断标准，很好

    addEvent(canvas,'mousedown',function(e){

//        console.log(e.offsetX + ' '+e.offsetY)

        down = true;

        x = e.offsetX;

        y = e.offsetY;

        clipArea(x, y,1,1);

    })

    addEvent(canvas,'mousemove',function(e){

        if(down){

            areaWidth = e.offsetX - x;

            areaHeight = e.offsetY - y;

            clipArea(x, y,areaWidth,areaHeight);

        }

    })

    addEvent(canvas,'mouseup',function(e){

        addEvent(canvas,'moumove',function(){});

        down = false;

        areaWidth = e.offsetX - x;

        areaHeight = e.offsetY - y;

        clipArea(x, y,areaWidth,areaHeight);

    })