How can I stop the screen flicker?

[Zerohawk]

All right, I'm taking an MFC class at my college right now, and been tasked by the prof to find someway to fix a problem the entire class had last year:

To simulate animation, the programs would periodically call the draw function, but this causes the whole screen to 'tear' and flicker. Since most of the programs turned in were games, this was a major draw back. We searched through all our text books, but couldn't find a solution to the problem.

So I turn to you. How can we fix this problem? By any means at all, any way to keep this tearing and flickering from happening, even if we have to learn to draw all over again.

[Ken Fitlike]

Search for 'double buffering' or 'back buffer' - essentially draw everything to an offscreen bitmap and, once all rendering is complete, draw that to the screen in a single step(see also CDC::BitBlt).

[novacain]

Double buffering is the best bet.....

Also look at the OnEraseBkgnd() handler (and return 0)

MFC is not that good for games due to the way it retrieves messages from the OS. Games update while there are no msg's.

Look at 'Idle Loop Processing' in MSDN

OnIdle() allows you to add functionality to the app when there are no msg's from the OS. But should not be used for lengthy operations.

this is the MFC message loop

	for (;;)
	{
		// phase1: check to see if we can do idle work
		while (bIdle &&
			!::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE))
		{
			// call OnIdle while in bIdle state
			if (!OnIdle(lIdleCount++))
				bIdle = FALSE; // assume "no idle" state
		}

		// phase2: pump messages while available
		do
		{
			// pump message, but quit on WM_QUIT
			if (!PumpMessage())
				return ExitInstance();

			// reset "no idle" state after pumping "normal" message
			if (IsIdleMessage(&m_msgCur))
			{
				bIdle = TRUE;
				lIdleCount = 0;
			}

		} while (::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE));
	}

This is slow as PumpMessage() calls GetMessage() which is additional overhead as msg has already been 'found' with PeekMessage().

Compare this to a game loop

MSG msg;


// prime loop
PeekMessage( &msg, NULL, 0, 0, PM_NOREMOVE);

// run till user exits

while (msg.message!=WM_QUIT) 
{
//use peek as it returns immediately
if (PeekMessage( &msg, NULL, 0, 0, PM_REMOVE)) 
{
        // dispatch the message
       TranslateMessage(&msg);
       DispatchMessage(&msg);

} 
else 
{
           // update and redraw screen
}