CG Basics - An Introduction to Computer Graphics for Artists - page 31

Fig. 2.25 Two examples of low diffi culty cartons
interface errors when you are working on critical models with a deadline hanging
over your head. The interface is how you communicate to your application and you
need to be very sure of yourself when using it.
The directions require a folding carton. The carton is the target , because the goal
is to aim for it, and match its appearance as closely as possible. To the extent this is
not accomplished, the target has been missed. The folding carton was chosen as a
target for highly specifi c reasons. First, it is a simple object. That is, most cartons do
not require more than about 200 polygons to make, some require as few as 50 or so.
This means that you can concentrate on fi nding mistakes and becoming familiar
with the tools without wasting time with polygons that do little more than multiply
the number of mistakes you make.
Folding the carton manually, particularly for certain cartons will require many
attempts to get right. This will force you to use the transformation tools repeatedly,
and will give you confi dence using those tools. It is important to understand the
connection between texture mapping, texture coordinates, and 3D models, so this
project gives you a way to see a 3D object as a map (the unfolded carton) before
folding it into a 3D object (the fi nished carton). Many modelers and texture artists
do not understand this simple connection, but the folding carton exercise should
make it clear to you. One last thing the project does is to sensitize you to how easy
it is to make mistakes. The goal is to make an error-free fi le. Anything less is a reason
to stick with the model until it is perfect before moving on.
Selecting the target object is an important part of the exercise. Some cartons
are easier to build than others. For reasons that are evident later, a carton built
exclusively out of parallel and perpendicular edges (Fig. 2.25 ) will be much easier
to construct than a carton that has tapered fold lines (Fig. 2.26 ).
The level of diffi culty may be increased if the carton is built with depth, instead
of as a fl at, two-sided polygon. A two-sided polygonal object is one where the
renderer has been instructed to render both sides of every face. This is not used
for objects that will never be seen from both sides because it increases render time
for the object. It is sometimes used to save render time, because a two-sided
polygon can be used in place of a larger polyset, required to defi ne the depth of an
object correctly.