Asset Creation: Maya Scenography Modeling - Creating Games with Unity and Maya - page 15

For our uses we will be focusing primarily on polygonal modeling techniques
(the techniques using the tools in Maya's Polygons mode). The other methods
of NURBS (non-uniform rational b-splines) and Subdivs are too indirect in their
creation of polygons, and thus we lose control over polygon placement and count.
Topology
Topology refers to the structure or organization of polygons on a surface.
Topology matters. Correctly structuring polygons makes a huge difference
in how the mesh can be deformed later (with things like joints), how the
form interprets collisions in Unity, and how easy it is to lay out UV maps.
Much of topology concern centers around the tessellation process—the
process of converting the form into three-sided polygons (tris) when it
comes time to render.
Maya, like most 3D software, allows the user to create polygons of any
number of sides (usually called n-gons). This is relatively new in the 3D
production history. Not many years ago, 3D software would allow polygons to
be constructed only as tris or quads (four-sided polygons). Tris are pretty hard
to work with and manipulate quickly, so quads became the preferred method
of organizing polygons. To allow artists to more fluidly create forms, most 3D
apps began allowing the user to pay no attention to the number of sides of a
polygon as the form was built. However, woe be the modeler who doesn't pay
attention to the construction of his polygons. Five- (and more) sided polygons
cause all sorts of problems down the road.
The issue is in the tessellation process. When the 3D software (or game engine,
like Unity) converts a 3D form into all tris (which it must for the video cards to
draw them), there are some shapes that are easier to tessellate. A quad is relatively
easy, since it just splits it in half from vertex to vertex ( Figure 2.4 ). However, the
tessellation of the n-gon is often unpredictable, especially from a game asset
creation standpoint. It does it for sure, but the resulting mesh is a mess ( Figure 2.5 ).
This messy tessellation that can be seen in Figure 2.5 may not seem to
be a big deal here, but when these polygons are subjected to distortion
techniques (like bending a mesh with joints), suddenly the edges where
things can actually bend end up being in unpredictable places and result in
Figure 2.4 Tessellating a quad is
pretty straightforward. Just split it
corner to corner to create two tris.