OpObj messages are fired when the player interacts with an obj on the ground, e.g. picking an obj up off the ground. This does not include examining objs.
whether the control key was held down, used to invert movement speed
the id of the obj interacted with
the option clicked, ranging from 1 to 5 (inclusive)
the absolute x coordinate of the obj on the ground
the absolute z coordinate of the obj on the ground