Primitives are the building blocks of 3Dbasic geometric forms that you can use as is or modify with transforms and Booleans (see Figure 3.24). Although it's possible to create most of these objects by lathing or extruding 2D shapes, most software packages build them in for speed and convenience.
FIGURE 3.24 Common 3D Primitives: (a) Cube. (b) Cylinder. (c) Tube. (d) Sphere. (e) Torus. (f) Cone.
The most common 3D primitives are cubes, pyramids, cones, spheres, and tori. Like 2D shapes, these primitives can have a resolution level assigned to them so that you can make them look smoother by boosting the number of sides and steps used to define them.
Inappropriate use of unmodified primitives is probably one of the most common novice mistakes. By their very nature, primitives have a mathematically perfect appearance that screams, "I am a 3D object!" As you will learn in Chapter 5, you're generally better off using less perfect 2D shapes as the basis for your 3D objects. Primitives are best suited as building blocks for more complex forms or for use in your scene's background, where any extra detail will be lost anyway. Also, primitives can be very useful as foreground objects when they're altered through the use of transforms and modifiers (more on this in Chapter 5).
Some programs may offer an array of additional, more sophisticated primitives that may be better suited to foreground use because they offer beveled or rounded edges instead of that "chopped-off 3D look" (see Figure 3.25). A number of these extended primitives would be a real chore to create from scratch, so they can be a time-saver in that regard as well.
FIGURE 3.25 "Extended" 3D primitives available in some programs provide beveled and radius edges as well as difficult-to-model shapes: (a) Filleted Cube. (b) Spindle. (c) Beveled Cylinder. (d) Torus Knot. (e) Capsule. (f) Star Polyhedron.
That about does it for building basic 3D objects. It's time to move on to the particulars of positioning these objects in 3D space. It's a big universe in there, so it's essential to know how to get around.