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.
