There were a few places throughout the SDL code where values were
clamped using SDL_min() and SDL_max(). Now that we have an SDL_clamp()
macro, use this instead.
Add a function to clamp a value to a range.
SDL_clamp(x, a, b) is equivalent to SDL_min(a, SDL_max(x, b)): it
ensures that x is not smaller than a, nor larger than b.
While, as best I can tell, this isn't actually standardised anywhere,
it's a very useful function/macro to have.
This was the original intent (note SDL_UpdateWindowGrab() in SDL_OnWindowFocusGained() and SDL_OnWindowFocusLost()) and fixes a bug where relative motion unexpectedly stops if the task bar is covering the bottom of the game window and the mouse happens to move over it while relative mode is enabled.
Another alternative would be to confine the mouse when relative mode is enabled, but that generates mouse motion which would need to be ignored, and it's possible for the user moving the mouse to combine with the mouse moving into the confined area so you can't easily tell whether to ignore the mouse motion. See https://github.com/libsdl-org/SDL/issues/4165 for a case where this is problematic.
This is the mouse focus except in the case where relative motion is enabled and the mouse is over a window floating on top of the application window (e.g. the taskbar)
This fixes restoring the cursor clip rectangle after the mouse has moved off of the window.
Also try to better synchronize cursor visibility with mouse position changes when changing relative mode. This doesn't work perfectly, but it seems to improve things on Windows.
On Wayland -- or at least on some Wayland implementations -- windows
aren't shown until something has been rendered into them. For the
'checkkeys' test program, this means that keyboard input isn't
registered, making the program rather useless.
By creating a renderer and presenting once, the window is properly
displayed, and the test behaves as it does under X11 (including
XWayland).
The exact same thing was done with testmessge in 1cd97e2695 (PR #4252)
Don't rely on checking __clang_major__ since it is not comparable
between different vendors. Don't use "#pragma clang attribute" since it
is only available in relatively recent versions, there's no obvious way
to check if it's supported, and just using __attribute__ directly (for
gcc as well) results in simpler code anyway.
The __clang_major__ and __clang_minor__ macros provide a marketing
version, which is not necessarily comparable for clang distributions
from different vendors[1]. In practice, the versioning scheme for
Apple's clang is indeed completely different to that of the llvm.org
releases. It is thus preferable to check for features directly rather
than comparing versions.
In this specific case, __builtin_bswap16 was being used with older
Apple clang versions that don't support it.
[1] https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
