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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