[Mesa-dev] Meson mesademos (Was: [RFC libdrm 0/2] Replace the build system with meson)

[Eric Anholt]

Jose Fonseca <jfonseca at vmware.com> writes:

> On 27/03/17 17:42, Dylan Baker wrote:
>> Quoting Jose Fonseca (2017-03-27 09:31:04)
>>> On 27/03/17 17:24, Dylan Baker wrote:
>>>> Quoting Jose Fonseca (2017-03-26 14:53:50)
>>>>> I've pushed the branch to mesa/demos, so we can all collaborate without
>>>>> wasting time crossporting patches between private branches.
>>>>>
>>>>>    https://cgit.freedesktop.org/mesa/demos/commit/?h=meson
>>>>>
>>>>> Unfortunately, I couldn't actually go very far until I hit a wall, as
>>>>> you can see in the last commit message.
>>>>>
>>>>>
>>>>> The issue is that Windows has no standard paths for dependencies
>>>>> includes/libraries (like /usr/include or /usr/lib), nor standard tool
>>>>> for dependencies (no pkgconfig).  But it seems that Meson presumes any
>>>>> unknown dependency can be resolved with pkgconfig.
>>>>>
>>>>>
>>>>> The question is: how do I tell Meson where the GLEW headers/library for
>>>>> MinGW are supposed to be found?
>>>>>
>>>>>
>>>>> I know one solution might be Meson Wraps.  Is that the only way?
>>>>>
>>>>>
>>>>> CMake makes it very easy to do it (via Cache files as explained in my
>>>>> commit message.)  Is there a way to achieve the same, perhaps via
>>>>> cross_file properties or something like that?
>>>>>
>>>>>
>>>>> Jose
>>>>
>>>> I think there are two ways you could solve this:
>>>>
>>>> Wraps are probably the most generically correct method; what I mean by that is
>>>> that a proper wrap would solve the problem for everyone, on every operating
>>>> system, forever.
>>>
>>> Yeah, that sounded a good solution, particularly for windows where's so
>>> much easier to just build the dependencies as a subproject rather than
>>> fetch dependencies from somewhere, since MSVC RT versions have to match
>>> and so.
>>>
>>>  > That said, I took a look at GLEW and it doesn't look like a
>>>> straightforward project to port to meson, since it uses a huge pile of gnu
>>>> makefiles for compilation, without any autoconf/cmake/etc. I still might take a
>>>> swing at it since I want to know how hard it would be to write a wrap file for
>>>> something like GLEW (and it would probably be a pretty useful project to wrap)
>>>> where a meson build system is likely never going to go upstream.
>>>
>>> BTW, regarding GLEW, some time ago I actually prototyped using GLAD
>>> instead of GLEW for mesademos:
>>>
>>>    https://cgit.freedesktop.org/~jrfonseca/mesademos/log/?h=glad
>>>
>>> I find GLAD much nicer that GLEW: it's easier to build, it uses upstream
>>> XML files, it supports EGL, and it's easy to bundle.
>>>
>>> Maybe we could migrate mesademos to GLAD as part of this work instead of
>>> trying to get glew "mesonfied".
>>>
>>>> The other option I think you can use use is cross properties[1], which I believe
>>>> is the closest thing meson has to cmake's cache files.
>>>>
>>>> I've pushed a couple of commits, the last one implements the cross properties
>>>> idea, which gets the build farther, but then it can't find the glut headers,
>>>> and I don't understand why, since "cc.has_header('GL/glut')" returns true. I
>>>> still think that wraps are a better plan, but I'll have to spend some time today
>>>> working on a glew wrap.
>>>>
>>>> [1] https://github.com/mesonbuild/meson/wiki/Cross-compilation (at the bottom
>>>> under the heading "Custom Data")
>>>
>>> I'm running out of time today, but I'll try to take a look tomorrow.
>>>
>>> Jose
>>>
>>
>> I'd had a similar thought, but thought of libpeoxy? It supports the platforms we
>> want, and already has a meson build system that works for windows.
>
> I have no experience with libepoxy.  I know GLAD is really easy to 
> understand, use and integrate.  It's completly agnostic to toolkits like 
> GLUT/GLFW/etc doesn't try to alias equivalent entrypoints, or anything 
> smart like libepoxy.
>
> In particular I don't fully understand libepoxy behavior regarding 
> wglMakeCurrent is, and whether that will create problems with GLUT, 
> since GLUT will call wglMakeCurrent..

libepoxy does "keep a vtable of resolved functions per context, wrap
wglMakeCurrent to trigger re-resolve when we change contexts".  For
handling things like glut's wglMakeCurrent, there's a public
epoxy_handle_external_wglMakeCurrent() function you can call.

If you use glut and fail to call epoxy_handle_external_wglMakeCurrent(),
you'll end up with resolution inside the global function pointers, which
is going to be fine if you only ever have one context in glut.

There's a note for "we should probably track the resolved functions per
context rather than throwing out resolution on every MakeCurrent", but
I don't actually know if anyone wants that.
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