BitmapDatas are a necessary part of a high performance game engine. Sometimes we can get away with haphazard BitmapData management, but more often than not, we need to be aware of where and how we are instantiating BitmapDatas so we can keep track of them and free up memory as appropriate. We also want to make sure we never instantiate two identical BitmapDatas. Today’s article presents a class for managing BitmapDatas which avoids some of the pitfalls associated with using Bitmaps.

Pretty Icons

The Pretty Icons used in the example code are courtesy of icojoy. Thanks guys!

BitmapLibraryManager

The BitmapLibraryManager is the class that we’re going to rely upon to manage our BitmapDatas. It is more capable than simply a BitmapDataManager (yes, this violates the Single Responsibility Principle) but the reality is that it is more useful as a ubiquitous manager tied to specific libraries. Yes, this also means it uses the often abused Singleton Pattern. Ease of use trumped both these (very important) considerations.

There are two ways to register a BitmapData with the BitmapLibraryManager, via registerBitmapData, which simply associates a BitmapData with a name, and via registerBitmapLibrary, which takes an instance of a class whose public properties are Bitmaps, and registers them based on the property name. If you’re unfamiliar with how to embed assets in your AS3 project, take a look at Embedding Assets in an AS3 Only Project. The example in the code project has an IconLibrary that looks something like this:

package
{
public class IconLibrary
{
    [Embed(source='../assets/icons/001_01.png')]
    public const Icon_001_01 : Class;
    [Embed(source='../assets/icons/001_02.png')]
    public const Icon_001_02 : Class;
...
}
}

To register and track all the bitmaps in our IconLibrary, we only need to register it:

BitmapLibraryManager.registerBitmapLibrary( new IconLibrary() );

When we need an instance of a Bitmap, we ask for one from the BitmapLibraryManager:

var myBitmap : Bitmap = BitmapLibraryManager.createBitmap( "Icon_001_01" );

This will guarantee there will only ever be one BitmapData for the associated asset, preventing us from inadvertently instantiating multiple identical versions of expensive memory intensive BitmapDatas.

For some memory metrics, the example code shows off some of memory savings of the BitmapLibraryManager method:

        /* TEST_NAIVE_INSTANTIATION
         * Naive method of just instantiating bitmap datas as we need them
         * Memory Used: 4603904
         */

        /* TEST_WORST_CASE_SCENARIO
         * Cloning the bitmap datas for every icon
         * Memory Used: 5672960
         */

        /* TEST_BITMAPLIBRARYMANAGER
         * Uses the bitmap library to manage bitmap data instantiation
         * Memory Usage: 3575808
         */

Yay! Memory savings. And it’s easier to clean up after them and instantiate them. Source code in the Google Project.