Tuesday, April 30, 2013

Hardware Acceleration in Android

Beginning in Android 3.0 (API level 11) we have the option to enable hardware acceleration.
Now what is hardware acceleration and why should we use it?

Hardware acceleration means that we use the GPU to do the drawing work instead of the CPU. The views on canvas will be exported to textures that will be drawn to the screen by using OpenGL libraries. This process is much faster then drawing them by using the CPU, however also much more memory consuming. Loading the OpenGL libraries takes 2 to 8 MB of main memory, if we eat even more memory by using large images or a lot of objects then on phones with limited memory we run into problems.

Because of the memory consumption Android does not allow images larger than 2048x2048 to be used during hardware accelerated events. Note that the actual image size might be even smaller since the image is first transformed to a texture, it is wise to not use images above 2000x2000. This means that if you want to work with larger images coming from camera's for example, you have to disable it.

Hardware acceleration can be switched on globally for the entire app in the manifest file.
<application android:hardwareAccelerated="true" ...>
But you can also enable it per activity and in the near future per window (not supported yet though), which would be more preferable since most applications would not profit from accelerated hardware in the main menu for example.

Crossplatform apps and hardware acceleration

In HTML5/JS cross-platform apps made by, for instance Phonegap/Cordova, hardware acceleration can improve the app significantly.
If we create a simple webapp with jQuery mobile and run it using Phonegap on a phone, we see that the transitions between pages are a bit staggering, the scrolling is not smooth and the reaction time is a bit slow, even on high-end phones.
Now we enable hardware acceleration and run the same app again. The transitions look amazing, scrolling is super smooth and the app reacts in no time!

In short: Hardware acceleration is an awesome new feature that Android 3.0 and above offers, but only use it when needed.