question: public static float ccpCalcRotate ( final CGPoint from , final CGPoint to ) { float o = to . x - from . x ; float a = to . y - from . y ; float at = ccMacros . CC_RADIANS_TO_DEGREES ( ( float ) Math . atan ( o / a ) ) ; if ( a < 0 ) { if ( o < 0 ) at = 180 + Math . abs ( at ) ; else at = 180 - Math . abs ( at ) ; } return at ; }
target:  Caculate the rotation(in degrees) between two points, so that when we move from one point to the other, we can set the correct rotation to head to that point.