setDX(newDX), setDY(newDY): Change motion in X or Y axis. If you
set the dx value to 5, for example, the sprite will move five pixels to the
right every frame until the dx value is changed again. The angle and
speed settings of the sprite will be affected by changes in dx and dy.
(This is why you must always use functions to change dx and dy — if
you change the properties directly, the speed and angle will no longer
be accurate.) The sprite will continue moving at the indicated speed and
direction until DX or DY is changed again directly or indirectly.