以一已知点为基点旋转另一点的方法
/** * 旋转点 * @param x * @param y * @param x1 * @param y1 * @param a */ _translatePoint:function(x,y,x1,y1,a){ var l = Math.sqrt(Math.pow(2,(x1-x)) + Math.pow(2,(y1-y))); var cosb= (x1-x)/l; var sinb = (y1-y)/l; var sina = Math.sin(a); var cosa = Math.cos(a); var cosc = cosa*cosb-sina*sinb; var sinc = sina*cosb+cosa*sinb; var $x = l*cosc; var $y = l*sinc; var point = [x+$x, y+$y]; return point; },