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Win32 GDI DoubleBuffering question

Started by justinrwalsh Jun 12, 2005 at 10:50 PM 5 replies 2.8k views

Original Post

Jun 12, 2005 at 10:50 PM

Ok im trying to implement double buffering and its not working and i cant find any articles on the toic, so here is what i am doing


HDC screenDC = GetDC(NULL);
HDC backDC = CreateCompatibleDC(screenDC);

TransparentImage( backDC,
		(LONG)posX, (LONG)posY, (LONG)width, (LONG)height, bitmapDC,
		0, 0, (LONG)width, (LONG)height,
		RGB(255, 0, 255));	//Going to make this constant for now

BitBlt(screenDC,
                    0, 0,
                    GetDeviceCaps(screenDC, HORZRES), GetDeviceCaps(screenDC, VERTRES),
                    backDC,
                    0, 0,
                    SRCCOPY);
	ReleaseDC(0, backDC);

Just turns the screen white. my objects do not draw... please help me!!!

NoMonkey

Jun 12, 2005 at 11:35 PM

That previous post was from me. Again, I hope it helps you out.

xllx_relient_xllx

Jun 12, 2005 at 11:45 PM

Double-buffing and memory-DC's

Maybe that'll help ya out.

relient.

justinrwalsh

Author

justinrwalsh

Jun 13, 2005 at 1:29 AM

Thank you, that was exactly what i was looking for.

thanks again.

Ravyne

294

Ravyne

Jun 13, 2005 at 1:50 AM

Just thought I'd mention that when you do get double-buffering working that it'll only be able to eliminate the flickering; you still may notice some shearing. There's unfortunately no way around this, as there's no way to force windows into copying the backbuffer during the vertical retrace, even though there really should be. You're also out of luck in detecting it yourself and trying to copy manually during the retrace because a) GDI doesn't expose the raster state to applications, and b) even if you knew it was happening, windows is message-based (read: not real-time) so theres no guarantee you'd get the messsage fast enough anyhow. The only way to respond to real-time events is to have the support of something at a lower level, like a device driver as OpenGL and DirectX do. I have seen one successful implimentation (which was a clever hack) which had the application spawning a custom device driver in a thread which implemented a callback to the render function though.

In any event, flickering is the real enemy, shearing isn't too bad and its the same effect you'd see in any game if you have the V-sync disabled.

justinrwalsh

Author

justinrwalsh

Jun 13, 2005 at 9:05 AM

Yeah i havnet noticed too much shearing, this is actually for the pocketPC. I really dont want to right my own blitters and get into the game api so i am going to use GDI stuff for very simple games, like the 80's rerto classics. But so far just double buffering tends to work pretty well, and elimenates the flicker all together.

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