3D game engine design and implementation (4) _ Engine

The architecture of each DLL has been done well, the interface also defined the corresponding part of the current program can be run, then how to proceed to the next design?
I first write all the message loop, and then create the window, based on the good main program, and then write the corresponding DirectX initialization part, is to write MM3DRenderDX9.dll module.
It is used to encapsulate all DX interfaces and provide it to the engine management module and, of course, to the UI part.
Next, you implement the UI part of the DLL. It is a texture to implement a 3D dialog box.
Well, write it here today, and continue to write code .... ..... ....... ...... ....... .....