Android Application Development

Chapter 12. Drawing 2D and 3D Graphics

The Android menagerie of widgets and the tools for assembling them are convenient, powerful, and cover a broad variety of needs. What happens, though, when none of the existing widgets offer what you need? Maybe your application needs to represent playing cards, phases of the moon, or the power diverted to the main thrusters of a rocket ship. In that case, you’ll have to know how to roll your own.

This chapter is an overview of graphics and animation on Android. It’s directed at programmers with some background in graphics, and goes into quite a bit of depth about ways to twist and turn the display. You will definitely need to supplement this chapter with Android documentation, particularly because the more advanced interfaces are still undergoing changes. But the techniques here will help you dazzle your users.

Rolling Your Own Widgets

As mentioned earlier, “widget” is a just convenient term for a subclass of android.view.View, typically for a leaf node in the view tree. Many views are just containers for other views and are used for layout; we don’t consider them widgets, because they don’t directly interact with the user, handle events, etc. So the term “widget,” although informal, is useful for discussing the workhorse parts of the user interface that have the information and the behavior users care about.

You can accomplish a lot without creating a new widget. Chapter 11 constructed applications consisting entirely of existing widgets or simple ...