Just An Application

August 22, 2009

A Standalone Android Runtime: UI And Graphics

Filed under: Android, Java, Mobile Java, Standalone Android Runtime — Tags: , , , — Simon Lewis @ 7:59 pm


The basis of the Android runtime graphics and UI functionality is the Skia graphics library and the SurfaceFlinger client/server architecture which are implemented in C/C++. In the case of the graphics functionality a large proportion of the classes in the android.graphics package are effectively Java wrappers around the equivalent C++ classes in Skia.

There is no direct equivalent to either Skia or the SurfaceFlinger in standard Java but there is sufficient graphics functionality available to substitute for enough of the functionality of Skia and the SurfaceFinger to produce at least basic UIs.


This is the standard locked screen showing the StatusBar and the KeyGuard. The resources, that is, the colours, drawables, and layouts used to produce them are unchanged, as are the fonts, and all the UI code involved. The battery charging animation works, as does the updating of the dates in the StatusBar and the KeyGuard. The only difference is that the rendering is being done in Java, as is the the composition. The top-level window is a java.awt.Frame


This is HelloWorld, Comparison with the emulator shows that is not quite right. Some of the padding in the title bar seems to have gone astray. This is probably down to the replacement resource handling code not doing the right thing.

One of the things that there is no support for in standard Java, not suprisingly, is the NinePatchDrawable. This is a specialized form of PNG. As both the StatusBar and the Activity title bar use them they have to be supported. The 9-patch specific information is contained a specialized chunk within the PNG the format. To make life interesting the exact format of this chunk is not documented, but it is possible to work out what it is with the aid of the source code.

Copyright (c) 2009 By Simon Lewis. All Rights Reserved.



  1. Wow, really cool! Well done

    Comment by Hamy — August 5, 2010 @ 4:34 am

    • PS – Did you release the patches or code to re-create this?

      Comment by Hamy — August 5, 2010 @ 4:35 am

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

Blog at WordPress.com.

%d bloggers like this: