This adds compile-time support for multiple platforms and runtime
detection of them. Window system related platform functions are now
called from shared code via the function pointer struct _GLFWplatform.
The timer, thread and module loading platform functions are still called
directly by name and the implementation chosen at link-time. These
functions are the same for any backend on a given OS, including the Null
backend.
The platforms are now enabled via CMake dependent options following the
GLFW_BUILD_<platform> pattern instead of a mix of automagic and ad-hoc
option names. There is no longer any option for the Null backend as it
is now always enabled.
Much of the struct stitching work in platform.h was based on an earlier
experimental branch for runtime platform selection by @ronchaine.
Every platform function related to windows, contexts, monitors, input,
event processing and Vulkan have been renamed so that multiple sets of
them can exist without colliding. Calls to these are now routed through
the _glfw.platform struct member. These changes makes up most of this
commit.
For Wayland and X11 the client library loading and display creation is
used to detect a running compositor/server. The XDG_SESSION_TYPE
environment variable is ignored for now, as X11 is still by far the more
complete implementation.
Closes#1655Closes#1958
POSIX.1-2008 deprecated gettimeofday, which we used as a fallback if the
monotonic clock was unavailable.
This replaces that fallback with the non-monotonic real-time clock.
Because of the Gordian knot of feature test macros across Unices, this
also includes the shift from some platform source files defining
_POSIX_C_SOURCE to various values to _DEFAULT_SOURCE being defined for
all source files on Linux. This is because -std=c99 on Linux disables
_DEFAULT_SOURCE (POSIX 2008 and extensions).
Once runtime platform selection comes in, this kind of platform-specific
preprocessor logic can be moved into the platform glue files and won't
need to be replicated by third-party build setups, but for now, sorry.
Inclusion of internal headers is already both centralized and follows
strict rules. Inclusion guards are both an unneccessary maintenance
burden and may hide inclusion order bugs.
