Game Development Reference
In-Depth Information
Why Do We Need LODs?
When a character is far off in the distance, essentially taking up few pixels on the screen,
there is no need for the character to have 4000 polygons when 100 or less will do.
This is where LODs come into play. What you do is take your main model and create four
versions, or five, or however many are needed, each one stepping down in its polygon
count. As the character moves away from the camera, a different version of the model is
loaded in its place. The farther away from the camera, the lower the version, until the char-
acter can no longer be seen.
If we use Kila as an example, her main model of 4094 polygons would more than likely be
usedforclose-upshots,ormaybejustincutscenes.ThenextLODforKila,then,wouldbe
the main one used in game, since we could remove around 1000 polygons and still retain
all the detail needed. The LOD after that would comprise 1000 polygons; then we'd drop
down to around 500; and the last one would be about 100 or 200. As you can see, we
step down gradually at first, before dropping dramatically as distance from the character
increases. We can do this because there will be decreasing need for detail as the character
moves farther away.
Tip
The graphics programmer usually sets the number of LODs and the num-
ber of polygons in each LOD. The trick is to have as few LODs as pos-
sible. One rule of thumb in the industry is “The sum polycount of all
LODs shouldn't exceed the main game model.”
You can see Kila with her levels of detail in
Figure 10.1
. Although there are fewer poly-
gons in the versions that are farther away, you cannot tell.
