If type is ::SDL_HAPTIC_CARTESIAN, direction is encoded by three positions
367     *  (X axis, Y axis and Z axis (with 3 axes)).  ::SDL_HAPTIC_CARTESIAN
uses
368     *  the first three \c dir parameters.  The cardinal directions would
be:
369     *   - North:  0,-1, 0
370     *   - East:  -1, 0, 0
371     *   - South:  0, 1, 0
372     *   - West:   1, 0, 0

typedef struct SDL_HapticDirection
{
    Uint8 type;         /**< The type of encoding. */
    Uint16 dir[3];      /**< The encoded direction. */
} SDL_HapticDirection;

An unsigned int can't store negative values and I don't see an alternate way to
encode them in the docs or source. The best I have been able to come up with is
using a negative magnitude for the effect but this will only get me 2 of the 4
quadrants in the plane for 2d effects. I looked at the win32 and linux
implementations and I believe is is safe to use signed ints in the direction
struct. I am unfamiliar with the darwin haptics API so I don't know if it is
safe.