Android™ Application Development - Bahar Ali Khan

Chapter 11: Advanced Android Development
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Anti-aliasing is particularly important when drawing text, as anti-aliased text can be signifi cantly easier
to read. To create even smoother text effects, you can apply the SUBPIXEL_TEXT_FLAG, which will
apply subpixel anti-aliasing.
You can also set both of these fl ags manually using the setSubpixelText and setAntiAlias methods,
as shown below:
myPaint.setSubpixelText(true);
myPaint.setAntiAlias(true);
Hardware Acceleration for 2D Graphics
In a boon for 2D graphics enthusiasts everywhere, Android lets you request that your application
always be rendered using hardware acceleration.
If hardware acceleration is available on the device, setting this fl ag will cause every View within the
Activity to be rendered using hardware. This has the side effect of dramatically improving the speed of
your graphics while reducing the load on the system processor.
Turn it on by applying the Window.FEATURE_OPENGL fl ag to your Activity using the
requestWindowFeature method, as shown below:
myActivity.requestWindowFeature(Window.FEATURE_OPENGL);
Unfortunately, Good Things seldom come for free, and this is no exception.
Not all the 2D drawing primitives available in Android are supported by hardware (notably most of the
Path Effects described previously).
Also, as your entire Activity is being effectively rendered as a single Canvas, invalidate requests on any
View will cause the whole Activity to be redrawn.
Canvas Drawing Best Practice
2D owner-draw operations tend to be expensive in terms of processor use; ineffi cient drawing routines
can block the GUI thread and have a detrimental effect on application responsiveness. This is particularly
true in a resource-constrained environment with a single, limited processor.
You need to be aware of the resource drain and CPU-cycle cost of your onDraw methods, to ensure you
don’t end up with an attractive application that’s completely unresponsive.
A lot of techniques exist to help minimize the resource drain associated with owner-drawn controls.
Rather than focus on general principles, I’ll describe some Android specifi c considerations for ensuring
that you can create activities that look good and remain interactive (note that this list is not exhaustive):
Consider Hardware Acceleration
❑ OpenGL hardware acceleration support for 2D graphics is
a Good Thing, so you should always consider if it’s suitable for your Activity. Good candidates
are Activities consisting of a single View with rapid, time-consuming updates. Be sure that the
primitives you use are supported by hardware.