SetRasterCallback on C# / BeefLang

[System64]

Hello! I'm trying Tilengine on BeefLang by curiosity and I'm trying to do raster effects.
The thing is when I execute SetRasterCallback, it asks for a videocallback :

private static extern void TLN_SetRasterCallback(VideoCallback callback);

I have no idea how to use it. Do you know how to use it please? It's the same thing for C#.