Game Development Reference
In-Depth Information
The importance of drawing
A sketch is very useful when creating low polygon models. By using the
sketch as a reference throughout the modelling process, the relative scale
of the polygons you use to define your character is constantly available.
The more accurate your drawing the easier you will find the modelling
process. I used the sketches shown in Figure 5.1 as a backdrop for the
Front and Side views when modelling 'Charlie'.
In the sketch the pencil suggests the stretching of the fabric of the
costume. In low polygon modelling you make no attempt to recreate these
creases with your geometry; this detail will be left for texture mapping,
which is covered in detail in the next chapter. The aim of your modelling
is to define the main volume of the character. You might find it useful while
modelling to add some relevant surface colours to your polygons to help
when judging the results.
Triangles or quads
Ultimately, your character is going to be a mesh that deforms as the
character goes through her paces. As she deforms her vertices, any
polygons that have more than three vertices will become non-planar.
Figure 5.2 (see page 82) shows the problems associated with non-planar
polygons. The polygon at the top left appears to be planar. As it rotates,
however, it is clear that it is far from planar. This situation causes the
render engine great difficulty in determining whether a polygon is front or
back facing. As you will recall, this is done using the order in which the
vertices appear when rendered on in screen coordinates. The same
diagram illustrates the polygon split into two triangles. Now it is clear how
the geometry should be rendered.
The problem of non-planar polygons is that the rendering software will
be considering triangles. If you have a four-sided polygon, then the
renderer will effectively split this into two triangles. If one of these triangles
is angled in such a way as to appear to be back facing, then your model
will develop holes. For this reason your mesh must be triangular. But
modelling with a triangular mesh is hard. It is always easier to model with
a combination of quads and triangles. So what to do about those quads.
All CGI packages have the ability to change a mesh into a triangular
mesh, but this is done without regard to the overall geometry. With low
polygon models the direction in which a quad is split into two triangles
makes a great difference to how the deforming mesh will appear when
animating. There are intelligent triple engines available that attempt to put
the edge where you would choose. No intelligent triple will do as good a
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