Graphics Reference
In-Depth Information
4
IV
4.1 Introduction
Demand for impressive graphics in mobile apps has given rise to ever-more pow-
erful GPUs and new graphics APIs such as OpenGL ES 3.0. These advances
enable programmers to write cleaner and more ecient implementations of com-
puter graphics algorithms than ever before. One particular area that stands to
benefit is the facial animation of characters in mobile games, a technique that is
commonly implemented using morph targets.
Morph target animation requires artists to pre-create multiple poses of a
model oine. Later on, during application execution, these poses are mixed to-
gether in varying quantities to create animation sequences such as blinking eyes
or a frowning face. When used in conjunction with skinning, the technique can
serve as the foundation of a feature-rich character animation system. Historically,
morph target animation has seen heavy use in PC and console games but a lack of
flexibility in earlier graphics APIs has led to complicated or expensive implemen-
tations on mobile platforms. This chapter describes an ecient implementation
of morph target animation that makes use of the transform-feedback API intro-
duced in OpenGL ES 3.0. The application in this chapter is a continuation of
the Gremlin demo, which was first introduced in a previous article [Senior 09].
The demo has been entirely rewritten and has been updated to take advantage
of OpenGL ES 3.0 on PowerVR Series6 mobile GPUs.
4.2 Previous Work
An interesting geometry texturing approach was suggested for mobile GPUs that
made use of the OpenGL ES 2.0 API [Senior 09]. This approach used a vertex
encoding scheme to store vertex displacements between target poses in textures.
