Question

I’ve a DLL (Player.dll) written in C++ that internally uses Windows GDI. I’ve an application (basically a video player) written in Windows Forms, that internally calls APIs from Player.dll to render the actual graphics on screen, using p/invoke technique:

public class ProxyPlayer
{
    [DllImport("Player.dll", CharSet=CharSet.Unicode, EntryPoint="PlayVideo")]
    public static extern void Play(int playerHandle, out TWResult result);

    [DllImport("Player.dll", CharSet=CharSet.Unicode, EntryPoint="PauseVideo")]
    public static extern void Pause(int playerHandle);

    //other methods
}

It’s working.

But now, I want to write the same application using Silverlight 4.0. As you know most Windows GDI works with HWND to render graphics on screen, that is why I pass playerHandle to ProxPlayer methods, as you can see above yourself. Window Forms’ UserControl defines a public property called Handle of type IntPtr which is equivalent to HWND, so I pass that to ProxyPlayer methods. It solved my problem. But Silverlight’s UserControl doesn’t have any such property.

So my question basically is, how would I get handle to my silverlight control? Because without it, I cannot call APIs from Player.dll. But I’ve to call APS from it. I don’t have any other options, as the DLL is actual engine that does literally everything related to interpreting a huge amount of data and then rendering them. So please suggest me solution that fits in with my requirement!

Note: Assume that my silverlight application will always run on Microsoft Windows. So I don’t have problem pinvoking Windows GDI.

Answer 1

If you can expose your native DLL as a COM Server that implements IDispatch, you can access that from Silverlight (via the AutomationFactory class) if you’re in an Out of Browser Trusted Application on Windows.

I still recommend (per my comment to Darin’s answer) that you take a good look at the platform, as your “PlayVideo”/”PauseVideo” example suggests you’re trying to do things the platform can likely already do – and better yet, the platform can do it on MacOS, and in-browser, and without the ugliness of writing your own COM Server, and so on.