Game Engine Architecture

38 1. Introduction

forms, including a binary space partitioning (BSP) tree, a quadtree , an octree ,

a kd-tree , or a sphere hierarchy. A spatial subdivision is sometimes called a

scene graph, although technically the latt er is a particular kind of data struc-

ture and does not subsume the former. Portals or occlusion culling methods

might also be applied in this layer of the rendering engine.

Ideally, the low-level renderer should be completely agnostic to the type

of spatial subdivision or scene graph being used. This permits diff erent game

teams to reuse the primitive submission code, but craft a PVS determination

system that is specifi c to the needs of each team’s game. The design of the

OGRE 3D open source rendering engine (htt p://www.ogre3d.org) is a great

example of this principle in action. OGRE provides a plug-and-play scene

graph architecture. Game developers can either select from a number of pre-

implemented scene graph designs, or they can provide a custom scene graph

implementation.

1.6.8.3. Visual Effects

Modern game engines support a wide range of visual eff ects , as shown in

Figure 1.21, including

z particle system s (for smoke, fi re, water splashes, etc.);

z decal systems (for bullet holes, foot prints, etc.);

z light mapping and environment mapping;

z dynamic shadows;

z full-screen post eff ects , applied aft er the 3D scene has been rendered to

an off screen buff er.

Scene Graph / Culling Optimizations

(BSP Spatial Subdivision Tree, kd-Tree, ...) Occlusion & PVS LOD System

Figure 1.20. A typical scene graph/spatial subdivision layer, for culling optimization.

Visual Effects

Particle & Decal

Systems Post Effects

HDR Lighting Subsurf. ScatterPRT Lighting,

Environment

Mapping

Dynamic ShadowsLight Mapping &

Figure 1.21. Visual effects.