Examples of Simple Windows Programs

Now, consider some examples. Listing 2.2 presents a simple program. I recommend that you study it carefully , since it will become a foundation for all materials that you will consider further. The window that appears when this program is started is shown in Fig. 2.1.

Figure 2.1: Window of the program presented in Listing 2.2

Pay special attention to the INCLUDELIB directives. MASM32 provides lots of libraries. For this example, you needed two of them: user32.lib and kernel32.lib.

Now, you need to define the constants and the library procedures.

All these definitions can be found in INCLUDE files supplied with MASM32. I will not use standard INCLUDE files for two reasons: by avoiding this approach, it is much easier to grasp the idea of programming and it simplifies the migration from MASM to TASM.

You must clearly understand the method of window procedure operation because it defines the entire Windows programming paradigm. The aim of this procedure is to ensure the correct reaction of the application to all incoming messages. Let me explain the operation of the application in detail. To begin with, note that unhandled messages must be returned to the system using the DefwindowProcA function. You must handle four messages: WM_CREATE , WM_DESTROY , WM_LBUTTONDOWN , and WM_RBUTTONDOWN . In terms of object-oriented programming, the WM_CREATE and WM_DESTROY messages play the roles of constructor and destructor, respectively. They arrive to the window function when the window is created or destroyed . If you click the small button with the x in the top right corner of the window, the WM_DESTROY message will arrive to the window function. After that, the PostQuitMessage function will be executed, and the WM_QUIT message will be sent to the function. This message will cause the message-handling loop to terminate. Then, the ExitProcess function will execute. This, in turn , will delete the application from the memory.

I'd like to draw your attention to the _ERR label. The jump to this label takes place if an error occurs. Here, it is possible to place an appropriate error message.

Listing 2.2: An example of a simple Windows application (MASM32)

 .386P ; Flat memory model .MODEL FLAT, stdcall ; Constants ; The message arrives when the window is closed WM_DESTROY          equ 2 ; The message arrives when the window is created WM_CREATE           equ 1 ; The message arrives if the left mouse button is clicked ; somewhere in the window area WM_LBUTTONDOWN      equ 201h ; The message arrives if the right mouse button is clicked ; somewhere in the window area WM_RBUTTONDOWN      equ 204h ; Window properties CS_VREDRAW          equ 1h CS_HREDRAW          equ 2h CS_GLOBALCLASS      equ 4000h WS_OVERLAPPEDWINDOW equ 000CF0000H Style               equ CS_HREDRAW+CS_VREDRAW+CS_GLOBALCLASS ; Standard icon identifier IDI_APPLICATION     equ 32512 ; Cursor identifier IDC_CROSS           equ 32515 ; Normal mode of displaying the window SW_SHOWNORMAL       equ 1 ; Prototypes of external procedures EXTERN MessageBoxA@16:NEAR EXTERN CreateWindowExA@48:NEAR EXTERN DefWindowProcA@16:NEAR EXTERN DispatchMessageA@4:NEAR EXTERN ExitProcess@4:NEAR EXTERN GetMessageA@16:NEAR EXTERN GetModuleHandleA@4:NEAR EXTERN LoadCursorA@8:NEAR EXTERN LoadIconA@8:NEAR EXTERN PostQuitMessage@4:NEAR EXTERN RegisterClassA@4:NEAR EXTERN ShowWindow@8:NEAR EXTERN TranslateMessage@4:NEAR EXTERN UpdateWindow@4:NEAR ; Directives for linking libraries includelib .c:\masm32\lib\user32.lib includelib c:\masm32\lib\kernel32.lib ;------------------------------------------ ; Structures ; Message structure MSGSTRUCT STRUC      MSHWND       DD ?   ; Identifier of the window                          ; that received the message      MSMESSAGE    DD ?   ; Message identifier      MSWPARAM     DD ?   ; Auxiliary information about the message      MSLPARAM     DD ?   ; Auxiliary information about the message      MSTIME       DD ?   ; Time of sending the message      MSPT         DD ?   ; Cursor position at the time of sending                          ; the message MSGSTRUCT ENDS ;------------ WNDCLASS STRUC      CLSSTYLE     DD ?   ; Window style      CLWNDPROC    DD ?   ; Pointer to the window procedure      CLSCEXTRA    DD ?   ; Information on auxiliary bytes for                          ; this structure      CLWNDEXTRA   DD ?   ; Information on auxiliary bytes for the window      CLSHINSTANCE DD ?   ; Application descriptor      CLSHICON     DD ?   ; Window icon descriptor      CLSHCURSOR   DD ?   ; Window cursor descriptor      CLBKGROUND   DD ?   ; Window brush descriptor      CLMENUNAME   DD ?   ; Menu identifier      CLNAME       DD ?   ; Specifies the window class name WNDCLASS ENDS ; Data segment _DATA SEGMENT      NEWHWND      DD 0      MSG          MSGSTRUCT <?>      WC           WNDCLASS <?>      HINST        DD 0 ; Here, the application descriptor is stored      TITLENAME    DB 'Simple example of a 32-bit application', 0      CLASSNAME    DB 'CLASS32', 0      CAP          DB 'Message', 0      MES1         DB 'You have clicked the left mouse button', 0      MES2         DB 'Exit. Bye!', 0 _DATA ENDS ; Code segment _TEXT SEGMENT START: ; Get application descriptor     PUSH 0     CALL GetModuleHandleA@4 ;     MOV [HINST], EAX REG_CLASS: ; Fill window structure ; Style     MOV [WC.CLSSTYLE], style ; Message-handling procedure MOV   [WC.CLWNDPROC], OFFSET WNDPROC MOV   [WC.CLSCEXTRA], 0 MOV   [WC.CLWNDEXTRA], 0 MOV   EAX, [HINST] MOV   [WC.CLSHINSTANCE], EAX ;----------Window icon PUSH  IDI_APPLICATION PUSH  0 CALL  LoadIconA@8 MOV   [WC.CLSHICON], EAX ;----------Window cursor PUSH  IDC_CROSS PUSH  0 CALL  LoadCursorA@8 MOV   [WC.CLSHCURSOR], EAX ;----------- MOV   [WC.CLBKGROUND], 17 ; Window color MOV   DWORD PTR [WC.CLMENUNAME], 0 MOV   DWORD PTR [WC.CLNAME], OFFSET CLASSNAME PUSH  OFFSET WC CALL  RegisterClassA@4 ; Create a window of the registered class PUSH  0 PUSH  [HINST] PUSH  0 PUSH  0 PUSH  400   ; DY - Window height PUSH  400   ; DX - Window width PUSH  100   ; Y - Coordinate of the window's top left corner PUSH  100   ; X - Coordinate of the window's top left corner PUSH  WS_OVERLAPPEDWINDOW PUSH  OFFSET TITLENAME ; Window name PUSH  OFFSET CLASSNAME ; Class name PUSH  0 CALL  CreateWindowExA@48 ; Check for errors CMP   EAX, 0 JZ    _ERR MOV   [NEWHWND], EAX ; Window descriptor ;--------------------- PUSH  SW_SHOWNORMAL PUSH  [NEWHWND] CALL  ShowWindow@8 ; Display the newly created window ;------------------------- PUSH  [NEWHWND] CALL  UpdateWindow@4 ; Redraw the visible part of the window ; WM_PAINT message ; Message-handling loop MSG_LOOP: PUSH  0 PUSH  0 PUSH  0 PUSH  OFFSET MSG CALL  GetMessageA@16 CMP   EAX, 0 JE    END_LOOP PUSH  OFFSET MSG CALL  TranslateMessage@4 PUSH  OFFSET MSG CALL  DispatchMessageA@4 JMP   MSG_LOOP END_LOOP: ; Exit the program (close the process) PUSH  [MSG.MSWPARAM] CALL  ExitProcess@4 _ERR: JMP   END_LOOP ;------------------------------------------ ; Window procedure ; Position of parameters in the stack ; [EBP+014H] LPARAM ; [EBP+10H] WAPARAM ; [EBP+0CH] MES ; [EBP+8] HWND WNDPROC PROC     PUSH  EBP     MOV   EBP, ESP     PUSH  EBX     PUSH  ESI     PUSH  EDI     CMP   DWORD PTR [EBP+0CH], WM_DESTROY     JE    WMDESTROY     CMP   DWORD PTR [EBP+0CH], WM_CREATE     JE    WMCREATE     CMP   DWORD PTR [EBP+0CH], WM_LBUTTONDOWN ; Left button     JE    LBUTTON     CMP   DWORD PTR [EBP+0CH], WM_RBUTTONDOWN ; Right button     JE    RBUTTON     JMP   DEFWNDPROC ; Clicking the right mouse button closes the window RBUTTON:     JMP   WMDESTROY ; Clicking the left mouse button LBUTTON: ; Displaying the message     PUSH  0 ; MB_OK     PUSH  OFFSET CAP     PUSH  OFFSET MES1     PUSH  DWORD PTR [EBP+08H]     CALL  MessageBoxA@16     MOV   EAX, 0     JMP   FINISH     WMCREATE:     MOV   EAX, 0     JMP   FINISH     DEFWNDPROC:     PUSH  DWORD PTR [EBP+14H]     PUSH  DWORD PTR [EBP+10H]     PUSH  DWORD PTR [EBP+0CH]     PUSH  DWORD PTR [EBP+08H]     CALL  DefWindowProcA@16     JMP   FINISH WMDESTROY:     PUSH  0 ; MB_OK     PUSH  OFFSET CAP     PUSH  OFFSET MES2     PUSH  DWORD PTR [EBP+08H] ; Window descriptor     CALL  MessageBoxA@16     PUSH  0     CALL  PostQuitMessage@4  ; WM_QUIT message     MOV   EAX, 0 FINISH:     POP   EDI     POP   ESI     POP   EBX     POP   EBP     RET   16 WNDPROC ENDP _TEXT ENDS END START