the SDL_Joystick to query.
the ball index to query; ball indices start at index 0.
stores the difference in the x axis position since the last poll.
stores the difference in the y axis position since the last poll.
true on success or false on failure; call SDL_GetError() for more information.
Get the ball axis change since the last poll.
Trackballs can only return relative motion since the last call to SDL_GetJoystickBall(), these motion deltas are placed into dx and dy.
Most joysticks do not have trackballs.