The first Direct3D task the WinMain function in D3dmain.cpp does is call the locally defined AppInit function, which creates the application window and initializes all objects needed to begin rendering. The WinMain function also implements the message pump for D3dmain.cpp and calls the locally defined RenderLoop and CleanUpAndPostQuit functions. The AppInit function calls other functions to help it do its work, and these functions, in turn, call still more functions; this group of initialization functions is the subject of most of this tutorial.
After performing some standard tasks in the initialization of a Windows application and initializing global variables to acceptable default settings, AppInit calls the InitScene function that each sample that uses D3dmain.cpp must implement. Simple sample applications, such as Oct1.c, implement versions of InitScene that do nothing but return TRUE. More complicated samples, such as Tunnel.c, use InitScene to allocate memory, generate points, and set global variables.
The last thing the AppInit function does before it returns is call the CreateD3DApp function, which is implemented in D3dmain.cpp. The functions called by CreateD3Dapp do much of the initialization work.