Some tricks with Peek Message

Introduction

Well I started off in VC++ after programming for sometime in VB (a few months at home). One function that I missed from VB was DoEvents. But I have found an equivalent one in VC++ using the function PeekMessage. Most of you might know these tricks but this is mainly for those who don't know how to do this.

Why I needed a DoEvent function.

Well I am in the midst of developing an interesting personal project,l the idea is a secret ;). So what happened was that I had a tight loop kind of a situation and I didn't want to use a thread because it was un-necessary. That's the time when I did start thinking about DoEvent equivalent in VC++.

DoEvent code

Well now enough of preaching :). Let's get back to the code that will help us in doing this.

static void DoEvents( HWND hWnd_i )
{
   MSG stMsg = { 0 };
   while( PeekMessage( &stMsg, hWnd_i, 0, 0, PM_REMOVE ))
   {
       TranslateMessage( &stMsg );
       DispatchMessage( &stMsg );
    }
}

Loop in which this is called is as follows...

for( UINT uFileIndex = 0; uFileIndex < uFileCount; ++uFileIndex )
{
   UpdateProgressBar( uFileIndex + 1 );
   if( !( uFileIndex % LOOP_THRESH_HOLD_FOR_DO_EVENTS ))
   {
      ResUtils::DoEvents( this->GetSafeHwnd() );
   }
}

I defined a LOOP_THRESH_HOLD_FOR_DO_EVENTS for calling this function. This will be useful if your loop is a low priority one. Now my GUI does not hang, painting takes place properly too.

Flushing Keyboard and Mouse Input buffer

Well this was about DoEvents. Now how about flushing keyboard input buffer and mouse input buffer selectively...

static void FlushKeyboardInputBuffer( HWND hWnd_i )
{
   MSG stMsg = { 0 };
   while( PeekMessage( &stMsg, hWnd_i , WM_KEYFIRST, WM_KEYLAST, PM_REMOVE ))
      ;
}

static void FlushMouseInputBuffer( HWND hWnd_i )
{
   MSG stMsg = { 0 };
   while( PeekMessage( &stMsg, hWnd_i, WM_MOUSEFIRST, WM_MOUSELAST, PM_REMOVE ))
      ;
}

Doing Idle time processing using PeekMessage

Conclusion

These are in fact a few of the ideas that I got while programming. Hope this helps. There are some other flags that you can pass to PeekMessage for eg:

PM_QS_INPUT	Windows 98/Me, Windows 2000/XP: Process mouse and keyboard messages.
PM_QS_PAINT	Windows 98/Me, Windows 2000/XP: Process paint messages.
PM_QS_POSTMESSAGE	Windows 98/Me, Windows 2000/XP: Process all posted messages, including timers and hotkeys.
PM_QS_SENDMESSAGE	Windows 98/Me, Windows 2000/XP: Process all sent messages.

On how to do Idle time processing using PeekMessage search MSDN with OnIdle keyword, you will bump into pretty interesting topics.

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Subject   Author  Date  Message 0x00AE in XP Ajay L D 4:31 21 Nov '06   Hi, The question I wanted to ask you is not related to the article you have published, but I wanted to ask it anyway! Do you have any idea about the message with value 0x00AE that we receive in XP? I received this message only if I use the Appearance as "XP style" in Display properties under the tab "Appearance". I was doing a paint in caption area (the place where Min, Max buttons are displayed) of an SDI, when I noticed that if I minimize and restore my application, the painting I did in caption area was getting overwritten with the default painting of the controls on the caption bar. I found that this undocumented message 0x00AE, caused this problem. The same message 0x00AE, does not come in Classic style. Any idea on this? Thank you, AJ Sign In·View Thread·PermaLink Re: Message 0x00AE in XP Nibu babu thomas 20:38 23 Nov '06   Ajay L D wrote: Any idea on this? Ooops no. I will keep this mind while working and if I find some situation similar to this I will tell you. Nibu thomas A Developer Programming tips[^]  My site[^] Sign In·View Thread·PermaLink Re: Message 0x00AE in XP helloworld2222 9:36 12 May '07   static void DoEvents( HWND hWnd_i ){MSG stMsg = { 0 };while( PeekMessage( &stMsg, hWnd_i, 0, 0, PM_REMOVE )){TranslateMessage( &stMsg );DispatchMessage( &stMsg );}} Well the loop in which I was calling this function is somewhat as follows: for( UINT uFileIndex = 0; uFileIndex < uFileCount; ++uFileIndex ){UpdateProgressBar( uFileIndex + 1 );if( !( uFileIndex % LOOP_THRESH_HOLD_FOR_DO_EVENTS )){ResUtils::DoEvents();} ....} well DoEvents(HWND hWnd_i) takes one parameter in definition. but when you call it you don't pass in anything. and what is with ResUtils? are you sure this is working? if you post something here and intended to help in solving problem, please post something which is error free and enough informative. Sign In·View Thread·PermaLink Re: Message 0x00AE in XP Nibu babu thomas 18:22 13 May '07   helloworld2222 wrote: well DoEvents(HWND hWnd_i) takes one parameter in definition. but when you call it you don't pass in anything. and what is with ResUtils? are you sure this is working? Yeah, it's taken from my personal project and it's working cool. As you said the actual code is static void DoEvents() { MSG stMsg = { 0 }; while( PeekMessage( &stMsg, AfxGetMainWnd()->GetSafeHwnd(), 0, 0, PM_REMOVE )) { TranslateMessage( &stMsg ); DispatchMessage( &stMsg ); } } That HWND parameter was added while writing this article, just to make sure users have enough flexibility to pass any HWND. helloworld2222 wrote: if you post something here and intended to help in solving problem, please post something which is error free and enough informative. That's why it's here. Nibu thomas A Developer Programming tips[^]  My site[^] Sign In·View Thread·PermaLink Re: Message 0x00AE in XP Romualdas Cukuras 3:01 24 May '07   0xAE WM_NCUAHDRAWCAPTION 0xAF WM_NCUAHDRAWFRAME Thats the secret shield of windows xp when you are using themes Good luck. Romas Sign In·View Thread·PermaLink

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