Programming Android

Chapter 9. Drawing 2D and 3D Graphics

The Android menagerie of widgets and the tools for assembling them are convenient and 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 the chapter with Android documentation, particularly because, especially with the advent of Honeycomb, the interfaces are still undergoing changes. But the techniques here will help you dazzle your users.

Rolling Your Own Widgets

As mentioned earlier, widget is just a convenient term for a subclass of android.view.View, typically a leaf node in the view tree. Internal nodes in the view tree, though they may contain complex code, tend to have simpler user interactions. 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. In this book, we have already constructed several applications consisting entirely of existing widgets or simple subclasses of ...