Re: WineD3D: move fake context code over to WGL

[Alexandre Julliard]

Roderick Colenbrander  writes:
> Subject: [PATCH] Move WineD3D_CreateFakeGLContext and friends over
> to WGL. For this we need a HDC and one received from lets say
> GetDC(0) won't do. Further this HDC needs CS_OWNDC set. For this
> reason we need our own window class.

Why does it need CS_OWNDC?  That sounds like a bug.

WineD3D: move fake context code over to WGL

[Chris Robinson]

On Tuesday 07 August 2007 06:54:37 am Alexandre Julliard wrote:
> Roderick Colenbrander  writes:
> > Subject: [PATCH] Move WineD3D_CreateFakeGLContext and friends over
> > to WGL. For this we need a HDC and one received from lets say
> > GetDC(0) won't do. Further this HDC needs CS_OWNDC set. For this
> > reason we need our own window class.
>
> Why does it need CS_OWNDC?  That sounds like a bug.

I ran across mailing list posts a while ago talking about OpenGL on Windows, 
and it mentioned that the window class had to have CS_OWNDC otherwise strange 
anomolies and crashes could pop up. Stefan Dösinger also said it's implied 
that D3D windows need the same. Searching google for 'opengl cs_owndc' 
brought up pages that mentioned buggy drivers need it, and as well, 
opengl.org's FAQ has it mentioned:

"error: Multiple access violations appear when running a Microsoft OpenGL 
MFC-based application.

solution: Set the CS_OWNDC style in the PreCreate*() routines in the view 
class."

http://www.opengl.org/resources/faq/technical/gettingstarted.htm

I can't say I know much about how HDCs work, but since OpenGL operates on HDCs 
and expects their state to remain constant through the life of the window, 
wouldn't it be a problem if DCs switched after a call to SetPixelFormat, or 
while it's part of the current context?

WineD3D: move fake context code over to WGL

[Joseph Garvin]

Alexandre Julliard wrote:
> Roderick Colenbrander  writes:
> > Subject: [PATCH] Move WineD3D_CreateFakeGLContext and friends over
> > to WGL. For this we need a HDC and one received from lets say
> > GetDC(0) won't do. Further this HDC needs CS_OWNDC set. For this
> > reason we need our own window class.
>
> Why does it need CS_OWNDC?  That sounds like a bug.

I came across this today in the wxWidgets library. Although it's not 
clear it affects newer windows versions, this comment tries to explain, 
quoting src/msw/glcanvas.cpp:

/*
  From Angel Popov

Here are two snips from a dicussion in the OpenGL Gamedev list that 
explains
  how this problem can be fixed:

"There are 5 common DCs available in Win95. These are aquired when you 
call
  GetDC or GetDCEx from a window that does _not_ have the OWNDC flag.
  OWNDC flagged windows do not get their DC from the common DC pool, the 
issue
  is they require 800 bytes each from the limited 64Kb local heap for GDI."

"The deal is, if you hold onto one of the 5 shared DC's too long (as 
GL apps
  do), Win95 will actually "steal" it from you.  MakeCurrent fails,
  apparently, because Windows re-assigns the HDC to a different window.  
The
  only way to prevent this, the only reliable means, is to set CS_OWNDC."
  */