Silverlight 2 Greasepole Game Engine
If you’re authoring multimedia applications in Silverlight, you might be interested in how each of the core game engine services for Legend of the Greasepole is now implemented for the Silverlight 2 Beta.
From C/C++ to a Provider Model-Based .NET Engine
Some brief history to explain how we got here: Greasepole’s first incarnation was manky C/C++ stuff that I’d perf-optimized to bits back in 1997-98. Trainwreck stuff.
Migrating that C/C++ mess to a C# mess involved writing a lot of Visual Studio 2008 macros. These macros could gain surprising insight into non-compiling half-C++, half-C# code, in order to sweep through and perform laborious changes.
Silverlight RenderingService
When each frame is rendered, the engine ultimately requests that the RenderingService draws a series of sprites from particular “frame descriptions” or “FrameDesc”s
The RenderingService pre-caches the URIs for the bitmap associated with each FrameDesc (e.g. “SilverLegendAssetsGame;component/Graphics/Frosh4a.BMP”) so that the bitmap can be looked up without string manipulation whenever it is requested by a sprite.
Silverlight SoundService
Sounds assets are stored as MP3 Resources in the previously-mentioned download-on-demand assemblies SilverLegendAssetsMenu.dll and SilverLegendAssetsGame.dll.
Just as with with RenderService, the SoundService pre-caches the URIs to all the sound files.
The SoundService keeps a static collection of MediaElements around. These are added as children to an invisible Canvas called SoundCanvas. When the engine requests that a sound is played, the SoundService finds an unused MediaElement in the static collection, sets its Source Property to the correct URI, and Play()s it.
The MediaElement’s MediaEnded event is handled to either loop the sound by either (1) setting .Position=TimeSpan.Zero and calling Play() again, or, (2) if it’s not looping, to add the MediaElement back to the static collection of available Media Elements.
Silverlight InputService
In the Silverlight 2 Beta, handling input was a piece of cake. Mouse and Keyboard events are handled for events on the main Canvas to inform the InputService of human interaction.
Silverlight GameTimerService
To create a game loop, Greasepole uses the “empty Storyboard technique” outlined at Silverlight Games 101. The game loop calls Update enough time to ensure a constant 24 updates-per-second update rate, and Render whenever possible, which triggers the RenderingService
Silverlight GameSettingsService
The IsolatedStorageFile API makes it very easy to rapidly save and load game settings in a local sandbox.
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