Game Engine Architecture

42 1. Introduction

SDK is now owned and distributed by NVIDIA, and the company is

adapting PhysX to run on its latest GPUs.

Open source physics and collision engines are also available. Perhaps the

best-known of these is the Open Dynamics Engine (ODE). For more informa-

tion, see htt p://www.ode.org. I-Collide, V-Collide, and RAPID are other popu-

lar non-commercial collision detection engines. All three were developed at the

University of North Carolina (UNC). For more information, see htt p://www.

cs.unc.edu/~geom/I_COLLIDE/index.html, htt p://www.cs.unc.edu/~geom/V_

COLLIDE/index.html, and htt p://www.cs.unc.edu/~geom/OBB/OBBT.html.

1.6.11. Animation

Any game that has organic or semi-organic characters (humans, animals, car-

toon characters, or even robots) needs an animation system. There are fi ve

basic types of animation used in games:

z sprite/texture an imation,

z rigid body hierarchy animation,

z skeletal animation,

z vertex animation, and

z morph targets.

Skeletal animation permits a detailed 3D character mesh to be posed by

an animator using a relatively simple system of bones. As the bones move, the

vertices of the 3D mesh move with them. Although morph targets and vertex

animation are used in some engines, skeletal animation is the most prevalent

animation method in games today; as such, it will be our primary focus in this

book. A typical skeletal animation system is shown in Figure 1.25.

Skeletal Animation

Animation

Decompression

Inverse

Kinematics (IK)

Game-Specific

Post-Processing

Sub-skeletal

Animation

LERP and

Additive Blending

Animation

Playback

Animation State

Tree & Layers

Figure 1.25. Skeletal animation subsystem.