Each Windowless*Application has now a companion Windowless*Context that
manages just the GL context creation and nothing else, with the ability
to just create the context and not make it current, so it doesn't affect
current thread state and can be moved to another thread and make current
there.
Other things that were done:
* Using `NoCreateT` instead of `nullptr` for creating the application
without creating GL context.
* Properly handling failed creation of Magnum context instance -- if it
errors out, also the GL context is destroyed to make it possible to
create the context with a different configuration.
* Reworked AMD and NVidia binary driver workaround, where core context
created with specific version doesn't automatically choose the newest
available (creating compatibility context on the other hand causes
the version to get stuck on 2.1 on Mesa and OSX).
* Added the above workaround also for WindowlessWglApplication to avoid
driver issues in the future.
* Reworked WindowlessWglApplication to not be so crazily entangled. It
was a misunderstanding on my side about how WINAPI works. Much
simpler now (and I hope still working :D).
Binary AMD drivers require the user to explicitly request the debug
context on context initialization, otherwise all debug functions are
no-op. This allows us to use debug functionality in command-line utils
and, mainly, GL functionality tests.
The Windows versions are coded without testing, so I hope I did not break
something :)
The parameterless Platform::Context::Context() constructor and
Platform::Context::tryCreate() function are deprecated in favor
functions that take argc/argv pair. The Context class now accepts
arguments starting with --magnum-* prefix. Currently there are none
except for the implicit --magnum-help, but that will change with the
following commits.
In some cases the GL context creation might success without error, but
the created version is one that we don't want (e.g. software GDI
rasterizer on Windows). Previously the Context class constructor just
exited the application and it was impossible to react on that from the
application side (for example reducing some context feature
requirements).
Now there is Platform::Context::tryCreate(), which returns either
created instance or `nullptr` if the instance creation failed with some
error. That is now used in all Platform::*Application implementations.
Vladimír Vondruš