SDL_JoyBallEvent

typedef struct SDL_JoyBallEvent
{
    Uint32 type;        /**< SDL_JOYBALLMOTION */
    Uint32 timestamp;   /**< In milliseconds, populated using SDL_GetTicks() */
    SDL_JoystickID which; /**< The joystick instance id */
    Uint8 ball;         /**< The joystick trackball index */
    Uint8 padding1;
    Uint8 padding2;
    Uint8 padding3;
    Sint16 xrel;        /**< The relative motion in the X direction */
    Sint16 yrel;        /**< The relative motion in the Y direction */
} SDL_JoyBallEvent;