Flickering bug for World of Warcraft

[Roderick Colenbrander]

> > Roderick Colenbrander wrote :
> > >> Hi,
> > >>
> > >> After investigating a bit in the Wine code, it seems that the
> > flickering 
> > >> bug of WoW in OpenGL mode is due to wglGetPbufferDCARB that returns a
> > DC 
> > >> which type is OBJ_MEMDC while it should return a DC which type is 
> > >> OBJ_DC. And since in the current git tree, the DC type of a Pbuffer
> is 
> > >> OBJ_MEMDC then the code located in lines 1394-1395 of 
> > >> dlls/winex11.drv/opengl.c is executed : the Pbuffer is copied to the 
> > >> screen each time the GL context is made current to the Pbuffer hence
> > the 
> > >> flickering (WoW bounds the GL context alternatively to the screen and
> > to 
> > >> the Pbuffer). The expected behaviour is not to copy the Pbuffer
> content
> > >> to the screen since WoW does it itself.
> > >>
> > >> The easiest workaround for this bug would be to make 
> > >> X11DRV_wglGetPbufferDCARB to return the Pbuffer's object->hdc (this 
> > >> fixes the flickering bug). However, I have made some tests with
> Windows
> > >> XP and it appears that wglGetPbufferDCARB returns a HDC different
> from 
> > >> the HDC passed when wglCreatePbufferARB was called. So such a patch 
> > >> would be a dirty hack not a real fix.
> > >>
> > >> I am not familiar enough with Wine to submit a patch so I leave the 
> > >> gurus out there find an elegant solution.
> > >>
> > >> Attached is the code that I used to perform a few tests about
> Pbuffers 
> > >> on Windows XP (code of interest is located from line 293 to line
> 298).
> > >>
> > >> Regards,
> > >>
> > >> Bertrand.
> > >>
> > >>
> > >>
> > > 
> > > It is correct that the return of OBJ_MEMDC causes the flickering as it
> > turns on the line glDrawBuffer. One of the reasons I started to rewrite
> > opengl32 was because of this. Right now most code is inside winex11.drv
> in
> > which we have much more control over things.
> > > 
> > > The easiest hack I thought about some months ago is to just set a flag
> > in the device returned wglGetPbufferDCARB though it would be tricky to
> get a
> > X11DRV_PDEVICE in a 'legal' (AJ-proof) way.
> > > 
> > > There's also a chance that a hack like this isn't needed at all.
> > Originally Huw Davies added the glDrawBuffer code together with
> X11DRV_SYNC_PIXMAP
> > code to winex11.drv/opengl32 in order to allow windowed opengl rendering
> > using DIBs. The glDrawBuffer line was used for emulating single
> buffering.
> > > 
> > > Recently Ulrich Czekalla worked on a better fix for the windowed
> opengl
> > problem using glScissors. For this patch various calls like glViewport,
> > glScissor and others need to be patched. It might be possible to get rid
> of
> > the glDrawBuffer / x11 pixmap rendering code but Huw would need to
> answer
> > that as he knows for what it was needed and it fully works.
> > > 
> > > I really hope it can be removed when the scissors code is in, it would
> > simplify the code and make my work easier.
> > > 
> > > Regards,
> > > Roderick
> > 
> > OK such a patch would remove the flickering bug for WoW but what about
> the
> > wrong 
> > type of the Pbuffer's DC ? Obviously, Windows XP attaches a DC which
> type
> > is 
> > OBJ_DC to the Pbuffers. I don't know if some apps rely on the assumption
> > that 
> > GetObjectType(wglGetPbufferDCARB(...)) == OBJ_DC, but if some do they
> > might 
> > behave wrongly with Wine.
> > 
> > Regards,
> > 
> > Bertrand.
> 
> I didn't have time yet to reply to the other email. This should be
> investigated more thoroughly. Second as this would be a 'serious' bug in Wine we
> need to convince Alexandre that this behavior is correct. For this purpose
> we need a test case. If you check the wine source you'll see that most dlls
> contain test cases using certain APIs. These testcases are used on wine and
> different windows versions to test the behavior of a function. Since the
> behavior of GetObjectType for this case is badly documented it should be
> added. Most likely it should be added to gdi32 and then dynamicly load
> opengl32.dll (you likely need to provide the function prototypes yourself if they
> aren't in wingdi.h as we don't have wine opengl headers yet).
> 
> If you could write such a test case in order to convince AJ that would be
> very usefull.
> 
> Regards,
> Roderick

Or perhaps a testcase isn't needed at all. I think the use of CreateCompatibleDC in wglGetPbufferDCARB is incorrect. According to MSDN this function creates a memory device context. Perhaps something like this works:
HDC hdc = CreateDC(...);
int format_orig = GetPixelFormat(hdc_orig);
SetPixelFormat(hdc, format_orig);
return hdc;
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