simple example of using ghost effect (zero is invisible, 100 is visible, in between is "ghost" like...) using the distiance from the mouse pointer to the sprite. Ghost effect value is calculated using the pythagorean theorem, the distance of the hypotenuse of the triangle formed by the sprite center point, the mouse pointer and the horizontal and vertical line that connects the triangle hypotenuse. Seems to work reasonably well, might be fun for sprites to "materialize" when close to something like the mouse pointer.
Thank you, Pythagoras -> http://en.wikipedia.org/wiki/Pythagoras
