Really aggravating
artifact of poorly-designed
3D systems. Due to the use of
clipping planes, only objects within a certain range of distances are rendered. So as you move towards a distant object, it will be invisible until the graphics subsystem decides that it's closer than the
far clipping
plane. Suddenly, it appears. (
Pop.) If you keep on going, getting closer and closer, many systems also have a
near clipping
plane, as well. A good
example is a race game where, as you drive down the course, bits of
scenery suddenly appear as you get close to them. The careful use of
fog will prevent this occurence, as will the design of sufficiently
twisty tracks, where you never see things which are that far away, because they're around a corner. This is also one reason why so many computer race courses have buildings/walls/trees/canyon walls/tubes around/along the track.
If Grover were to do the near and far demonstration on a cheap box, you might get pop-up, and the opposite, pop-down.