2.2 The Dinosaur Model

The task of figuring out how to describe the 3D object you wish to render is called modeling. Much as a plastic airplane model is constructed out of little pieces, a computer generated 3D scene must also be built out of little pieces. In the case of 3D rendering, the pieces are generally polygons.

The dinosaur model to be displayed is constructed out of a hierarchy of display lists. Rendering the dinosaur is accomplished by executing a single display list.

The strategy for modeling the dinosaur is to construct solid pieces for the body, arms, legs, and eyes. Figure 2 shows the 2D sides of the solids to construct the dinosaur. Making these pieces solid is done by extruding the sides (meaning stretching the 2D sides into a third dimension). By correctly situating the solid pieces relative to each other, they form the complete dinosaur.

The work to build the dinosaur model is done by the routine named makeDinosaur. A helper routine extrudeSolidFromPolygon is used to construct each solid extruded object.

• 2.2.1 The GLU Tessellator
• 2.2.2 Hierarchical Display Lists
• 2.2.3 Back-face Culling