Adds a new shape to the sprite, in addition to any it already has. These additional shapes only apply to physics sprites and must be added after a sprite has been set to use physics.
The circle is defined by specifying its center point relative to the sprite's current offset and a radius. For example, if the circle was to be centered on the sprite's offset point it would be specified at position 0,0. Any other value will offset the circle from the sprite. The radius is defined in x coordinates, due to world coordinates not necessarily representing the size of items on screen (e.g. 10 units in X may not be the same apparent size as 10 units in Y).
This will recalculate the sprite's mass and center of mass values.
AddSpriteShapeCircle( iSpriteIndex, x, y, radius )