Message loop

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Sasha

Joined: 17 Nov 2011
Posts: 93

Sasha 03 Jun 2013, 14:30

GetMessage returns zero when the wm_quit is posted. It returns -1 on error, and nonzero when there is other messages. Nonzero doesn't mean 1

The code from the Template example.

Code:

  msg_loop:
        invoke  GetMessage,msg,NULL,0,0
        cmp     eax,1
        jb      end_loop  
        jne     msg_loop  ;we are in dead loop when GetMessage returns -1

;we are here when eax==1

        invoke  TranslateMessage,msg
        invoke  DispatchMessage,msg
        jmp     msg_loop

  error:
        invoke  MessageBox,NULL,_error,NULL,MB_ICONERROR+MB_OK

  end_loop:        ;eax=0
        invoke  ExitProcess,[msg.wParam]

This example works. That means, that GetMessage actually returns 1(And not any other NONZERO). But the right way to do somethig like this.(Actually, I use this code)

Code:

  messageLoop:
        invoke  GetMessage,Msg,0,0,0
        cmp     eax,0 
        jle     EndLoop
        invoke  TranslateMessage,Msg ;eax>0 signed
        invoke  DispatchMessage,Msg
        jmp     MessageLoop

  endLoop:
        jnz     GetMessageError ;eax==-1 

        invoke  ExitProcess,[Msg.wParam] ;eax==0

03 Jun 2013, 14:30

bitRAKE

Joined: 21 Jul 2003
Posts: 4060
Location: vpcmpistri

bitRAKE 03 Jun 2013, 14:36

http://blogs.msdn.com/b/oldnewthing/archive/2013/03/22/10404367.aspx

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¯\(°_o)/¯ “languages are not safe - uses can be” Bjarne Stroustrup

03 Jun 2013, 14:36

Sasha

Joined: 17 Nov 2011
Posts: 93

Sasha 03 Jun 2013, 14:46

Just after posting this, I understood, that my axample goes to error on ALL negative numbers. Here is another, better example:

Code:

 MessageLoop:
        invoke  GetMessage,Msg,0,0,0
        or      eax,eax
        je      finish
        inc     eax
        je      GetMessageError
        invoke  TranslateMessage,Msg
        invoke  DispatchMessage,Msg
        jmp     MessageLoop

03 Jun 2013, 14:46

Sasha

Joined: 17 Nov 2011
Posts: 93

Sasha 03 Jun 2013, 14:55

bitRAKE wrote:

http://blogs.msdn.com/b/oldnewthing/archive/2013/03/22/10404367.aspx

Thanks. Your article says, that if you're sure in the parameters you are passing to GetMessage, means they are hardcoded and tested in compiler time you will never get a -1

03 Jun 2013, 14:55

Sasha

Joined: 17 Nov 2011
Posts: 93

Sasha 03 Jun 2013, 15:07

The code in Ddraw example and also, I've seen this somewhere else, uses GetMessage after the PeekMessage shows that there is a message pending. Why not just get it with PM_REMOVE?

Code:

  messageLoop:
        invoke  PeekMessage,Msg,NULL,0,0,PM_REMOVE
        or      eax,eax
        jne     ismessage

  dosomething:

;Do something

        jmp     messageloop

  ismessage:
        cmp     [Msg.message],WM_QUIT
        je      finish
        invoke  TranslateMessage,Msg
        invoke  DispatchMessage,Msg
        jmp     messageloop

  finish:
        invoke  ExitProcess,[Msg.wParam]

03 Jun 2013, 15:07

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 04 Jun 2013, 21:16

Sasha wrote:

Thanks. Your article says, that if you're sure in the parameters you are passing to GetMessage, means they are hardcoded and tested in compiler time you will never get a -1

There is more to it. I made a quick glance at my User32.DLL, 6.1.7601.17514 (win7sp1_rtm.101119-1850). It reveals something quite different from what MSDN says about GetMessageA(): if wMsgFilterMin has any bit higher than 16th set (seems funny because Hungarian prefix w implies that even 16th bit can't be set Wink

) or wMsgFilterMax too, except when wMsgFilterMax==-1 (i.e. condition is wMsgFilterMin & ~0x1FFFF || wMsgFilterMax & ~0x1FFFF && wMsgFilterMax != -1), function sets ERROR_INVALID_PARAMETER status and returns 0 (not -1 as one may expect).

As about PeekMessage(…, PM_REMOVE), it's better to handle input in separate thread than to intersperse output routine with occasional input checks. Your suggestion seems pretty valid though (another method may be using WM_TIMER for redraws).

04 Jun 2013, 21:16

Sasha

Joined: 17 Nov 2011
Posts: 93

Sasha 05 Jun 2013, 12:12

I'm thinking about putting the entire window creation to a separate thread. To have something like CreateWindowAsync.
I think that filtering messages and hwnds is not a good thing.

05 Jun 2013, 12:12

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