; template for program using standard Win32 headers
format PE GUI 4.0
entry start

include '%fasminc%\win32a.inc'

section '.data' data readable writeable

     _title db 'Win32 program template',0
     _class db 'FASMWIN32',0

     mainhwnd dd ?
     hinstance dd ?

     msg MSG
     wc WNDCLASS

section '.code' code readable executable
     start:
          invoke    LoadCursor,0,IDC_ARROW
               mov  [wc.hCursor],eax    ;will see hourglass (busy)
                                        ;cursor if this line is clear
                                        ;some delay perhaps
               mov  [wc.lpfnWndProc],WindowProc
               mov  [wc.lpszClassName],_class
               mov  [wc.hbrBackground],COLOR_BTNFACE+1 ;will see transparent window
                                                       ;if this line is clear
          invoke    RegisterClass,wc
          invoke    CreateWindowEx,\
                    0,\
                    _class,\
                    _title,\
                    WS_VISIBLE+WS_DLGFRAME+WS_SYSMENU,\
                    128,128,\
                    192,192,\
                    NULL,\
                    NULL,\
                    [hinstance],\
                    NULL
               mov  [mainhwnd],eax

     msg_loop:
          invoke    GetMessage,msg,NULL,0,0
                    or   eax,eax
                    jz   end_loop
          invoke    TranslateMessage,msg
          invoke    DispatchMessage,msg
                    jmp  msg_loop

     end_loop:
          invoke    ExitProcess,[msg.wParam]

proc WindowProc, hwnd,wmsg,wparam,lparam
                    cmp  [wmsg],WM_DESTROY
                    je   wmdestroy
     defwndproc:
          invoke    DefWindowProc,[hwnd],[wmsg],[wparam],[lparam]
                    jmp  finish
     wmdestroy:
          invoke    PostQuitMessage,0
     finish:
          return
endp

section '.idata' import data readable writeable

  library kernel,'KERNEL32.DLL',\
       user,'USER32.DLL'

  import kernel,\
      ExitProcess,       'ExitProcess'

  import user,\
      RegisterClass,     'RegisterClassA',\
      CreateWindowEx,    'CreateWindowExA',\
      DefWindowProc,     'DefWindowProcA',\
      GetMessage,        'GetMessageA',\
      TranslateMessage,  'TranslateMessage',\
      DispatchMessage,   'DispatchMessageA',\
      LoadCursor,        'LoadCursorA',\
      PostQuitMessage,   'PostQuitMessage'
    

;2. why we need to

        push    ebx esi edi

;in the actual "template.asm" -> proc WindowProc,hwnd,wmsg,wparam,lparam
;and pop them off in the finish:
    

int PASCAL WinMain
       (HINSTANCE hInstance,
 HINSTANCE hPrevInstance,
    LPSTR lpszCmdLine,
  int nCmdShow)
    

You call getModule handle only if you need a reference to the module, in most win applications you need it at least to create a window (the [hinstance] gets it value from the function call),

You push the registers because they need (or you want them) to be saved after the function call.

Eg. GetModuleHandle for hInstance etc.

GetModuleHandle will always return the same address value (0400000h)

HMODULE GetModuleHandle(
     LPCTSTR lpModuleName   // module name
);
    

2. it's calling standard, caller awaits to have those values preserved. It is same when you call some API procedure, you await it won't change value of this registers.

anyway, vid, do you mean that "push ebx esi edi" and pop them off later in the end of WindowProc has becoming so common (a tradition for win32 asm guys) that now already emerges as a "Standard" when you wrote in message #4

i wish if you could verify my understanding, does this mean, in win32 ASM world, the WINAPI will ONLY modify the EAX register? and if it(winapi) need to uses the ebx,esi,or edi, it will push them first and pop them off later?

does the WINAPI or Windows use the "ebx esi edi"? and what are those registers function as in win32 operating system?

vb, you really should read a decent ASM and Win32ASM tutorial. Sure you can learn from forums, but some questions are TOO basic. Besides ebx, edi, and esi there is not only eax. Yes, the push ebx esi edi is so common that some functions take it as granted so use this push and pop to avoid some bugs.