Graphics Programs Reference
In-Depth Information
2.
Press C to subdivide and then V to return to the rough polygon mesh. You
will notice that while the surface changes, the lines that mark the original
polygons do not. In any layer of subdivision within Silo, the base mesh
remains editable.
3.
Subdivide again and try moving a few edges and points using the
manipulator to get a feel for how the subdivided surface responds. You
are always selecting and working with the faces, edges, and vertices of the
low-resolution original, from which the subdivided version is created.
Subdivision is an iterative command, meaning each time you press C you'll
get a smoother and smoother mesh, and each time you press V you'll step
back one level. One temptation for beginning modelers is to use as high a
subdivision level as they can. However, because each level quadruples the
number of visible polygons from the previous level, going too high can take
a toll on your computer processor and dramatically slow modeling. It is best
to use low levels of subdivision (typically three or less) and jump up to higher
levels only periodically if needed.
Along with all the benei ts, subdivision can reveal and magnify certain kinds of
modeling l aws. As mentioned earlier, this is why it plays a role in determining
the basic rules of polygon modeling—although it is not the only factor.
Magnii ed l aws caused by subdivision are known as subdivision artifacts, and
are essentially unexpected bumps, snags, or other types of visual problems.
In Figure 2.2, you can see how adding triangles to a model (something we will
discuss avoiding in the next section) did not cause a visible problem in the
base mesh, but did create a bump in the subdivided version.
I nvoking the Holy Quad
One concept you will see reinforced throughout this topic is the importance
of modeling almost exclusively using four-sided polygons, or “quads.” As a new
Using non-quads in a mesh is one way to create subdivision artifacts.
FIG. 2.2
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