Child Windows and Owned Windows

Later, you will see many times that windows have numerous attributes. In addition, windows can be related to each other in a certain way. In other words, every window can have a parent window and several child windows. A window that has no parent is called a top-level window. All examples considered previously demonstrated top-level windows. Elements located in the window ( buttons , lists, etc.) are child windows. In addition to child windows, there are owned windows. An owned window has an owner but is not a child window to it. Examples of owned windows are so-called pop-up windows used for building various dialog panels. The main difference between a dialog box and an owned window is that the child window can be moved only within an area limited by the area of the parent window and an owned window can be moved anywhere within the screen area. The behavior of the parent window influences the behavior of its child and owned windows:

When the parent window is minimized or maximized, all its child and owned windows are also hidden or restored.
When the parent window is moved, all its child windows move with it (this doesn't relate to owned windows).
When the parent window is destroyed, all its child and owned windows are destroyed .

Child windows with the common parent window can overlap. The order, in which such windows are displayed, is called Z-order and can be regulated using special API functions, such as SetWindowPos , DeferWindowPos , and GetNextWindow. Later, I won't concentrate on this topic.

Listing 3.4 shows a program that demonstrates the properties of child and owned windows (Fig. 3.2). When this program is started, its main window appears. When the user clicks the mouse within its client area, two windows appear: the child window and the owned window. To better understand their properties, I recommend that you experiment with these windows.

Figure 3.2: Main window with one child window and one owned window (see Listing 3.4)

Listing 3.4: A program that creates a main window and two secondary windows

 .586P ; Flat memory model .MODEL FLAT, stdcall ;--------------------------------------- ; Constants ; The message that arrives when the window is closed WM_DESTROY          equ 2 ; The message that arrives when the window is created WM_CREATE           equ 1 ; The message that arrives when the user clicks the left mouse ; button in the client area of the window WM_LBUTTONDOWN      equ 201h ; Window properties CS_VREDRAW          equ 1h CS_HREDRAW          equ 2h CS_GLOBALCLASS      equ 4000h WS_OVERLAPPEDWINDOW equ 000CF0000H WS_POPUP            equ 80000000h WS_CHILD            equ 40000000h STYLE               equ CS_HREDRAW+CS_VREDRAW+CS_GLOBALCLASS BS_DEFPUSHBUTTON    equ 1h WS_VISIBLE          equ 10000000h WS_CHILD            equ 40000000h STYLBTN             equ WS_CHILD+BS_DEFPUSHBUTTON+WS_VISIBLE ; Standard icon identifier IDI_APPLICATION     equ 32512 ; Cursor identifier IDC_ARROW           equ 32512 ; Window display mode -- normal 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 GetMessageA016: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 ; Structures ; Message structure MSGSTRUCT STRUC MSHWND     DD ? MSMESSAGE  DD ? MSWPARAM   DD ? MSLPARAM   DD ? MSTIME     DD ? MSPT       DD ? MSGSTRUCT ENDS ;---- Window class structure WNDCLASS STRUC CLSSTYLE   DD ? CLWNDPROC  DD ? CLSCBCLSEX DD ? CLSCBWNDEX DD ? CLSHINST   DD ? CLSHICON   DD ? CLSHCURSOR DD ? CLBKGROUND DD ? CLMENNAME  DD ? CLNAME     DD ? WNDCLASS ENDS ;------------------------------------------ ; INCLUDELIB directives for the linker to link libraries includelib c:\masm32\lib\user32.lib includelib c:\masm32\lib\kernel32.lib ;------------------------------------------ ; Data segment _DATA SEGMENT NEWHWND    DD 0 MSG        MSGSTRUCT <?> WC         WNDCLASS <?> HINST      DD 0 ; Application descriptor TITLENAME  DB 'Child and owned windows', 0 TITLENAMED DB 'Child window', 0 TITLENAMEO DB 'Owned window', 0 CLASSNAME  DB 'CLASS32', 0 CLASSNAMED DB 'CLASS321', 0 CLASSNAMEO DB 'CLASS322', 0 _DATA ENDS ; Code segment _TEXT SEGMENT START: ; Get the application descriptor   PUSH   0   CALL   GetModuleHandleA@4   MOV    [HINST], EAX REG_CLASS: ; Fragment in which the main window is registered ; Style   MOV    [WC.CLSSTYLE], STYLE ; Message-handling procedure   MOV    [WC.CLWNDPROC], OFFSET WNDPROC   MOV    [WC.CLSCBCLSEX], 0   MOV    [WC.CLSCBWNDEX], 0   MOV    EAX, [HINST]   MOV    [WC.CLSHINST], EAX ;----------Window icon   PUSH   IDI_APPLICATION   PUSH   0   CALL   LoadIconA@8   MOV    [WC.CLSHICON], EAX ;---------- Window cursor   PUSH   IDC_ARROW   PUSH   0   CALL   LoadCursorA@8   MOV    [WC.CLSHCURSOR], EAX ;----------Registration of the main window   MOV    [WC.CLBKGROUND], 17 ; Window color   MOV    DWORD PTR [WC.CLMENNAME], 0   MOV    DWORD PTR [WC.CLNAME], OFFSET CLASSNAME   PUSH   OFFSET WC   CALL   RegisterClassA@4 ; Fragment in which the child window is registered ; Style   MOV    [WC.CLSSTYLE], STYLE ; Message-handling procedure   MOV    [WC.CLWNDPROC], OFFSET WNDPROCD   MOV    [WC.CLSCBCLSEX], 0   MOV    [WC.CLSCBWNDEX], 0   MOV    EAX, [HINST]   MOV    [WC.CLSHINST], EAX ;-------------   MOV    [WC.CLBKGROUND], 2 ; Window color   MOV    DWORD PTR [WC.CLMENNAME], 0   MOV    DWORD PTR [WC.CLNAME], OFFSET CLASSNAMED   PUSH   OFFSET WC   CALL   RegisterClassA@4 ; Fragment in which the owned window is registered ; Style   MOV    [WC.CLSSTYLE], STYLE ; Message-handling procedure   MOV    [WC.CLWNDPROC], OFFSET WNDPROCO   MOV    [WC.CLSCBCLSEX], 0   MOV    [WC.CLSCBWNDEX], 0   MOV    EAX, [HINST]   MOV    [WC.CLSHINST], EAX ;-------------   MOV    [WC.CLBKGROUND], 1 ; Window color   MOV    DWORD PTR [WC.CLMENNAME], 0   MOV    DWORD PTR [WC.CLNAME], OFFSET CLASSNAMEO   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   600 ; DX Window width   PUSH   100 ; Y  Coordinate of the top left corner   PUSH   100 ; X  Coordinate of the top left corner   PUSH   WS_OVERLAPPEDWINDOW   PUSH   OFFSET TITLENAME ; Window name   PUSH   OFFSET CLASSNAME ; Window class   PUSH   0   CALL   CreateWindowExA@48 ; Check for error   CMP    EAX, 0   JZ     _ERR   MOV    [NEWHWND], EAX ; Window descriptor ;------------------------------------------   PUSH   SW_SHOWNORMAL   PUSH   [NEWHWND]   CALL   ShowWindow@8 ; Show the newly created window ;------------------------------------------   PUSH   [NEWHWND]   CALL   UpdateWindow@4 ; Redraw the visible part of the window, the WM_PAINT message ; Message-processing 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 ;************************************ ; Main 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   JE     LB   JMP    DEFWNDPROC WMCREATE:   MOV    EAX, 0   JMP    FINISH LB: ; Create the child window   PUSH   0   PUSH   [HINST]   PUSH   0   PUSH   DWORD PTR [EBP+08H]   PUSH   200 ; DY Window height   PUSH   200 ; DX Window width   PUSH   50 ; Y Coordinate of the top left corner   PUSH   50 ; X Coordinate of the top left corner   PUSH   WS_CHILD OR WS_VISIBLE OR WS_OVERLAPPEDWINDOW   PUSH   OFFSET TITLENAMED ; Window name   PUSH   OFFSET CLASSNAMED ; Window class   PUSH   0   CALL   CreateWindowExA@48 ; Create an owned window   PUSH   0   PUSH   [HINST]   PUSH   0   PUSH   DWORD PTR [EBP+08H]   PUSH   200 ; DY Window height   PUSH   200 ; DX Window width   PUSH   150 ; Y Coordinate of the top left corner   PUSH   250 ; X Coordinate of the top left corner   PUSH   WS_POPUP OR WS_VISIBLE OR WS_OVERLAPPEDWINDOW   PUSH   OFFSET TITLENAMEO ; Window name   PUSH   OFFSET CLASSNAMEO ; Window class   PUSH   0   CALL   CreateWindowExA@48 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   CALL   PostQuitMessage@4 ; WM_QUIT message   MOV    EAX, 0 FINISH:  POP EDI   POP    ESI   POP    EBX   POP    EBP   RET    16 WNDPROC ENDP ;************************************ ; Child window procedure ; Position of parameters in the stack ; [EBP+014H] ; LPARAM ; [EBP+10H]  ; WAPARAM ; [EBP+0CH]  ; MES ; [EBP+8]    ; HWND WNDPROCD  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   JMP    DEFWNDPROC WMCREATE:   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:   MOV    EAX, 0 FINISH:   POP    EDI   POP    ESI   POP    EBX   POP    EBP   RET    16 WNDPROCD ENDP ;************************************ ; Procedure of the owned window ; Position of parameters in the stack ; [EBP+014H] ; LPARAM ; [EBP+10H]  ; WAPARAM ; [EBP+0CH]  ; MES ; [EBP+8]    ; HWND WNDPROCO 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   JMP    DEFWNDPROC WMCREATE:  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:   MOV    EAX, 0 FINISH:   POP    EDI   POP    ESI   POP    EBX   POP    EBP   RET    16 WNDPROCO ENDP _TEXT ENDS END START

It is necessary to mention that to translate the program presented in Listing 3.4 using TASM, in addition to the changes that are common and already known to you, it is necessary to add the @@ prefix (the locality indicator) to the names of matching labels from different procedures and to insert the LOCALS directive in the beginning of the program. MASM automatically considers all labels encountered within the procedure as local. In TASM, however, the situation is more complicated. More information on local labels will be provided in Chapters 11 and 12.

Note that for each of the three windows, a separate message-handling procedure is defined. Message-handling procedures for the child and owned windows do not contain a PostQuitMessage command. This is natural, because closing a child or owned window must not initiate program termination. In all other respects, the contents of the window procedures for this window can be the same as for the main (or top-level) window. They can contain controls, have headers, process any messages, and so on.