Using ccp helper methods

In the example of Rocket Through, the game we developed in Chapter 5, On the Line – Rocket Through, we used vectors to describe movement, and now I want to show you the logic behind some of the methods we used to handle vector operations and what they mean.

Rotating the rocket around a point

Let's start, as an example, with the rocket sprite moving with a vector of (5, 0):

We then draw a line from the rocket, say from point A to point B:

Now we want the rocket to rotate around point B. So how can we change the rocket's vector to accomplish that? With Cocos2d-x, we can use the helper point method rotateByAngle to rotate a point around any other point. In this case, we rotate the rocket's position point around point B by a certain angle.

But here's a question – in which direction should the rocket rotate?

By looking at this figure, you know that the rocket should rotate clockwise, since it's moving towards the right. But programmatically...