The pixel number of each side of retina Device is double of non-retina device. When using UIPanGestureRecognizer,i can get velocity of the pan in pixels/second in the coordinate system of the specified view by calling - (CGPoint)velocityInView:(UIView *)view,but do I need divide the return value by 2 to get a correct velocity?I have read the document from apple,developer do not take care the x2 problem.But the comment in UIPanGestureRecognizer.h make me confuse.
No, it returns it in points per second, that is not pixels per second.
Apple chose for points as a unit because it is not dependent on the pixel densitiy of the screen. Meaning that the 3G and the iPhone 4 have the exact same result with this gesture recognizer. The iPhone5 has a bigger screen but that doesn't change anything you have to do with what the recognizer returns.
Thus to your answer: No, you should not divide it by 2, apple is taking care in their API's.