Game Development Reference
In-Depth Information
Figure 2.5
Microsoft Flight Simulator X.
Consider the problem of a flight simulator like Microsoft Flight Simulator X. When the
plane is on the ground, the display looks a lot like every other 3D game out there. You see
a few buildings, a few other planes, and a runway. You might also see some scenery in the
distance, such as a mountain range or a city skyline (see Figure 2.5).
Once the plane is up in the air, you have a different story altogether. You
'
ve
increased the viewable surface by a few orders of magnitude, and therefore you
ve
increased the potential viewable set of polygons. Players who attempt a naive
approach of simply drawing all the polygons will learn quickly that they can
'
t get
their plane more than 150 feet off the ground. The frame rate will fall in inverse geo-
metric proportion to the altitude of the plane because that
'
'
s how many more poly-
gons you have to draw to achieve a realistic look.
The actual approach to this problem uses different levels of detail to draw areas of
terrain and objects, depending on their distance from the viewer. On some flight
simulators, you can catch this happening. Simply begin a slow descent and watch as
the terrain suddenly becomes better looking; the green patches will increase in detail
and eventually become individual trees until you crash into them. One of the trickier
parts of most 3D engines is getting the levels of detail to transition smoothly, avoid-
ing the
“
popping
”
effect.
