I made a specific yet advanced game playing AI but I want to bring it to D to make it cross platform

[Gan via Digitalmars-d]

I've written an AI to play a game in Objective-C on Mac. The AI 
bits are mostly C++ code for performance. I want to make the AI 
cross platform because the game has a huge windows user base. My 
hope is to get other programmers interested in helping out 
because it is very time consuming to make perfect screen 
detection and AI decisions.

My question is, to write the Mac and Windows specific code in 
their respective languages(C# and Obj-C) for UI, screen capture 
and input simulation; can I have that code be usable from D? I 
don't know much about shared libraries or importing DLLs so I 
have no knowledge on the possibility. I would like to write all 
the AI code in D but have all the OS specific code written in 
their own languages that I can call from D. I am very familiar 
with writing C#, Obj-C and even D code. I just don't know how to 
make them all play nice. Maybe there's a way to compile the OS 
specific code in libraries and D can call them depending on which 
OS the D code gets compiled to?

Would anyone know how to do this? Or have basic examples?
To start I'd just like to write a D program that can call some 
specific already compiled C# or Obj-C code that will create a UI 
window but maintain full control in D such that D could issue 
further already compiled commands. Also receive input, like a 
button is clicked and that button sends an event notifier back to 
D.

Is this plausible?