And the question is - how to include a window inside the window? I want to include at my main window with options and buttons one other with Direct3d graphics on another thread.

If you are using Microsoft's MFC you can use a splitter window.

No I'm using Win32 API which I write on the title. Can somebody tell me the function?

What have you tried? My first thought is to make window B and child of window A and set its coordinated within that of window A. You do that in the CreateWindow() function call.

What have you tried? My first thought is to make window B and child of window A and set its coordinated within that of window A. You do that in the CreateWindow() function call.

Ok I solved it - put a new window on another thread and coordinate it at the main window with special properties.