Game Engine Architecture

424 10. The Rendering Engine

10.1.2.6. Materials

A material is a complete description of the visual properties of a mesh. This

includes a specifi cation of the textures that are mapped to its surface and also

various higher-level properties, such as which shader programs to use when

rendering the mesh, the input parameters to those shaders, and other parame-

ters that control the functionality of the graphics acceleration hardware itself.

While technically part of the surface properties description, vertex att ri-

butes are not considered to be part of the material. However, they come along

for the ride with the mesh, so a mesh-material pair contains all the informa-

tion we need to render the object. Mesh-material pairs are sometimes called

render packets, and the term “geometric primitive” is sometimes extended to

encompass mesh-material pairs as well.

A 3D model typically uses more than one material. For example, a mod-

el of a human would have separate materials for the hair, skin, eyes, teeth,

and various kinds of clothing. For this reason, a mesh is usually divided into

submeshes , each mapped to a single material. The Ogre3D rendering engine

implements this design via its Ogre::SubMesh class.

10.1.3. Lighting Basics

Lighting is at the heart of all CG rendering. Without good lighting, an other-

wise beautifully modeled scene will look fl at and artifi cial. Likewise, even the

Figure 10.19. A variation on the classic “Cornell box” scene illustrating how realistic lighting

can make even the simplest scene appear photorealistic.