Microsoft decided some time ago to stop developing the MDX libraries and thus never release the 2.0 version. Instead they migrate the library to XNA, which is a managed game engine shared with XBox360. It has not yet been announced that DirectX 10 will be incorporated into Xna. So IUnknown is the only way to use Dx10. First the XNA beta SDK can only install on C# Express. If you already has VS2005 thats pretty lame. Fortunately a "msiexec -a" can extract the install files so you can grab the Microsoft.Xna.* assemblies and use in VS2005. Using the MDX2 beta I built a pretty fast 2D library, and it was not as easy to port to Xna as I had hoped because lots of functionality is missing.
- Shader is everything. Fixed function pipeline is gone so for instance View/World/Projection is handled by a shader. If you want your primitives to be anything but gray, you must also write a shader.
- You can no longer fill the vertexbuffer using Lock/Unlock - only SetData can be used. I was very sad to see this as it's much faster to fill the buffer directly than the extra pin/memcpy used by SetData. DirectSound has been completely replaced by XACT. I haven't yet figured out how to render realtime sound data.