[waffle] [GSOC 2014] How to deal with non win32 api, wgl(Create, Make)Context depends on existing window

Sat May 31 11:59:19 PDT 2014

----- Original Message -----
> On 24/05/14 20:28, Emil Velikov wrote:
> > Hi all,
> > 
> > Another round of interesting bits and bulbs.
> > 
> Bit of an update:
> 
> > The email came out a bit longer than expected, although it provides a
> > decent
> > list of possible solutions. Let me know which one you'll go with.
> > 
> > Four topics sorted by priority - high to low (based on my humble opinion)
> > 
> > * ChoosePixelFormat - close yet quite different across platforms.
> > 
> >   - glXChoosePixelFormat    - depends on display (matches waffle's model).
> >   - CGLChoosePixelFormat    - no dependencies.
> >   - {wgl,}ChoosePixelFormat - depends on a device_context/existing window.
> > 
> To make things better, wgl functions depend on a current context as well. The
> recommended way of doing things under windows seems to be the following:
> 
>    window_handle = CreateWindow(...)
>    device_context = GetDC(window_handle);
> 
>    gl_rendering_context = wglCreateContext(device_context);
>    wglMakeCurrent (device_handle, gl_rendering_context);
> 
>    // any of the following
>    wglGetProcAddress(...)
>    wglChoosePixelFormat(...)
>    ....
> 
>    wglMakeCurrent (device_handle, NULL);
>    wglDeleteContext (gl_rendering_context);
> 
>    ReleaseDC(device_context);
>    DestroyWindow(window_handle);

Yep.

> 
> AFAICS waffle is unique wrt other projects (apitrace, epoxy, glut) as it
> allows the PixelFormat to be called prior to the creation of either window or
> context.
> 
> >   Options:
> >     - Create a window, choose format, destroy window.
> >           No guarantee that the function will behave the same for another
> >           window/device_context.

In practice, the odds of this happening are very low.

I'd recommend creating an invisible window, do your things then, keep the window around, and then merely double check later that things are not busted.

You can see in http://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/state_trackers/wgl/stw_ext_pbuffer.c how to create an invisible window  (This is how Mesa implements pbuffers on Windows!.)

Jose

> >     - or, create window, choose format, reuse window on
> >     waffle_window_create()
> >           Sanest solution. If windows is not created just make one (i.e.
> >           waffle_config_choose is not executed before
> >           waffle_window_create).
> > 
> >     - or, store the attributes, and invoke ChoosePixelFormat as
> >       waffle_window_create is executed.
> >           What if code-flow depends on waffle_config_choose's return value
> >           ?
> > 
> >     - or rework waffle API ... (no, please no)
> > 
> >   Suggestion:
> >     "Cache" the window, and reuse it on waffle_window_create.
> > 
> I'm planning to give the "cache the windows" a stab soon, although
> I would greatly appreciate if anyone has an opinion/comment.
> 
> > 
> > * CreateContext, MakeCurrent - same story as ChoosePixelFormat :\
> > 
> > 
> > * Thread-safe and Co.
> > AFAICS it's used to provide thread independent waffle error info. Have I
> > missed something ?
> > 
> >    - strerror_r is depreciated in favour of strerror_s. MS claims that the
> >      former is not TS, while *nix man page disagrees.
> > 
> >    - Current mingw-w64 build does not work on Win XP - missing strerror_s.
> >      Fix landed in mingw-w64 trunk ~a few weeks ago.
> > 
> >        - Back-port commit and build things with custom mingw_w64
> >        - or, port the commit over to waffle ?
> > 
> >   Suggestion:
> >     Port over to waffle.
> > 
> The commit addressing strerror_s + mingw-w64 + WinXP has been backported to
> the stable branch of mingw-w64. We can mandate that version (to be released)
> as the minimum requirement in the readme/build-scripts.
> 
> > 
> > * Library dependencies, etc. (low priority)
> > libwaffle-1.dll depends on mingw-w64 dlls - should we nuke the dependency,
> > ship them in the zip or leave it to the user/dev ?
> > 
> >   Library:
> >     libgcc_s
> >       __emutls_get_address
> >       __udivdi3
> >       __umoddi3
> > 
> >   Options:
> >     - Static link libgcc_s, generally not bad idea
> >     - or, rework waffle ?
> >           Split merged_version or move to (major << 8 | minor) for the
> >           wcore_config_attrs_version_* helpers - will nuke the last two.
> >           No idea how to nuke __emutls_get_address.
> > 
> >   Suggestion:
> >     Split to separate major/minor.
> > 
> As spotted by Jordan, there should be no implications of static linking with
> libgcc[1]. I've added a couple of lines to the build and so far it works like
> a charm.
> 
> [1]
> https://urldefense.proofpoint.com/v1/url?u=https://www.gnu.org/licenses/gcc-exception-3.1-faq.html&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=NMr9uy2iTjWVixC0wOcYCWEIYhfo80qKwRgdodpoDzA%3D%0A&m=nPzAHYznyFhyA6Bn%2FXHt2AeHO%2FNhVm9VWwNYkwnEmIc%3D%0A&s=f1ea3aad8cc771542f8ab3be427e2335d4486e0516e7e738e83019b3457a475c
> 
> > 
> >   Library:
> >      libwinpthread-1
> >        pthread_key_create
> >        pthread_mutex_lock
> >        pthread_mutex_unlock
> >        pthread_once
> >        pthread_setspecific
> > 
> >   Options:
> >      - Static link
> >      - or, rebuild mingw-w64-gcc with --enable-threads=win32
> >      - or, rework current code (open to suggestions)?
> > 
> >   Suggestion:
> >     The above list states my order of preference.
> > 
> > 
> My initial assumption was that the library is GPL 2 and/or 3 based.
> 
> Closer look revealed that it is X/MIT and 3-clause BSD licensed, and afaik
> there should be no problems with distributing the binary (pending the no
> advertisement & stating it's license).
> 
> 
> Meanwhile I did take a look at how greatly piglit depends on waffle. Nicely
> separated codebase, falling back to glut whenever waffle is not available.
> 
> A couple more patches have emerged as well
>  * Autodetect the targets under linux, and
>  * Remove the restrict definition from waffle.h
> 
> which I would like to test a bit more and send it out for review.
> 
> Cheers
> Emil
> 
> > Any feedback would be great. Meanwhile I will send out a few misc/cleanup
> > patches :)
> > 
> > Cheers,
> > Emil
> > 
> 
> _______________________________________________
> waffle mailing list
> waffle at lists.freedesktop.org
> https://urldefense.proofpoint.com/v1/url?u=http://lists.freedesktop.org/mailman/listinfo/waffle&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=NMr9uy2iTjWVixC0wOcYCWEIYhfo80qKwRgdodpoDzA%3D%0A&m=nPzAHYznyFhyA6Bn%2FXHt2AeHO%2FNhVm9VWwNYkwnEmIc%3D%0A&s=75e8e52e86f672b4713712855cfb9e53b8decd445b5a1083dc66360bae412284
> 