GNOME Mutter requires keyboard grab for certain important functionality like
window resizing, interaction with the application context menu, and opening the
Activites view. To allow Mutter to grab the keyboard as needed, we'll ungrab
when the mouse leaves our window.
To be safe, we'll do this for all WMs since forks of Mutter and Matacity (and
possibly others) may have the same behavior, and we don't want to have to keep
track of those.
The grabbed_window field is superfluous now since SDL added the
SDL_GetGrabbedWindow() function, so it can be removed.
DirectFB_SetWindowMouseGrab() is also simplified because SDL handles ungrabbing
any previously grabbed window prior to calling SetWindowMouseGrab() now.
Compile-tested only.
SDL_SetKeyboardFocus(NULL) will lift any keys still pressed when keyboard focus
leaves the window, but then key repeat comes behind our backs and presses the
key down again. This results in an infinite stream of SDL_KEYDOWN events when
focus leaves the window with a key down (particularly noticeable with Alt+Tab).
This gives us flexibility to add others hints to control keyboard grab behavior
without having to touch all of the backends. It also allows us to possibly
expose keyboard grab separately from mouse grab for applications that want to
manage those independently.
Wayland compositors seem to have standardized on 10 units per "wheel tick" for
continuous scroll events, so we need to convert these axis values to ticks by
dividing by 10 before reporting them in SDL_MOUSEWHEEL events.
Use zwp_keyboard_shortcuts_inhibit_manager_v1 to allow SDL applications
to capture system keyboard shortcuts like Alt+Tab when keyboard grab is
enabled via SDL_HINT_GRAB_KEYBOARD.
Calling open() on input devices can generate device I/O which blocks
the main thread and causes dropped frames. Using stat() we can avoid
opening anything unless /dev/input has changed since we last polled.
We could have used something fancy like inotify, but it didn't seem
worth the added complexity for this uncommon non-udev case.
The 10 ms delay effectively caps input polling at 100 Hz and rendering
at 100 FPS if applications use these functions in their event loop. The
delay may also lead to dropped frames even at 60 FPS due if they are
unlucky enough to hit the delay and rendering takes longer than 6 ms.
https://bugzilla.libsdl.org/show_bug.cgi?id=4350
We can't safely call GL_DestroyRenderer() until GL_LoadFunctions()
succeeds because we will be missing functions that we try to use
when activating the renderer for destruction if we have an GL context.
Creating a full-screen SDL renderer on Windows will keep the screensaver
suspended by DirectX, as is default for full-screen DX applications. However,
for applications that render in windowed-mode, the screensaver will
still kick in, even if SDL_DisableScreenSaver() is called or
SDL_HINT_VIDEO_ALLOW_SCREENSAVER is set to 0 (default). Implementing
a SuspendScreenSaver() function for Win32 fixes this behavior.
Cameron Gutman