Flickering bug for World of Warcraft

[Roderick Colenbrander]

> 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
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