Class Diagrams for AnimTour3D

Chapter 19. Animated 3D Sprites

This chapter and the next deal with sprite animation. The Sprite3D class of Chapter 18 possesses a rudimentary kind of animation, allowing the entire sprite to be moved over the XY plan and rotated around the y-axis. The kind of animation we'll be discussing here allows parts of the figure to move; for example, to have a robot wave its arms, jump, or turn its head.

There are three common animation approaches:

• Keyframe animation

• Figure articulation

• Figure articulation with skinning

Keyframe animation is similar to the technique used in the 2D Sprite class from Chapter 11. However, instead of using a sequence of 2D images, a sequence of 3D models is used. Each model is represented by the same figure but is positioned slightly differently; rapid switching between the models creates the illusion of sprite movement. Poses can be organized into an animation sequence, so, for example, walking is represented by a sequence of different leg positions. A sequence is typically triggered by the user pressing a key (e.g., the down arrow, to move the sprite forward) or by other external events. A simple keyframe animation system is developed in this chapter.

Figure articulation represents a figure (or any articulated model) as a series of interconnected components. These components typically represent the limbs of a figure and can be moved and rotated. The movement of one limb affects the limbs connected to it, usually through the process of forward or inverse kinematics. Figure articulation with forward kinematics is detailed in Chapter 20.

Figure articulation with skinning extends the articulation technique by layering a mesh (skin) over the limbs (bones). As limbs move, the mesh is automatically moved and distorted to keep the components covered. Links and further information on skinning are provided in Chapter 20.