Don't call the roundtrip in ShowWindow unless restoring a previously hidden window. This fixes a regression in GNOME when creating a window with the fullscreen flag set, as the fullscreen window will be positioned down the screen by the height of the top bar if the window is made fullscreen on the primary display and the roundtrip is called when initially displaying the window.
SDL_CreateWindow() may call GetWindowDisplayIndex() to compute the position
of a new window that the caller has requested to be placed on a certain
display. Since we haven't fully constructed the window yet, our driverdata
will be nil and we will fail to get the NSScreen (which is fine). However,
we need to return an error (not 0, which is a valid display index) for
SDL_GetWindowDisplayIndex() to know to figure out the display index itself.
Fixes positioning new windows on secondary displays when using
SDL_WINDOWPOS_CENTERED_DISPLAY() and SDL_WINDOWPOS_UNDEFINED_DISPLAY().
OpenGL windows don't actually get the WM_WINDOWPOSCHANGED event in the SetWindowPos() call in WIN_SetWindowFullscreen(), so setting the window size to zero never gets reset and we're stuck with a zero sized window.
Instead, just force the resize event in WM_DPICHANGED handling, where we know we need it. If we end up needing to force it in WIN_SetWindowFullscreen(), just set a flag in the window data and respond to that in WM_WINDOWPOSCHANGED, but that's a fairly risky behavior change as suddenly all applications would start getting SDL_WINDOWEVENT_SIZE_CHANGED when going fullscreen, and they may respond to that in expensive and potentially disruptive ways.
For later we'll probably create a DPI changed event and respond to that in the renderer instead of this window size changed hack.
This fixes https://github.com/libsdl-org/SDL/issues/6033 @ericwa
The video core assumes that window->w/h will be updated before returning
from SetWindowFullscreen(). This is needed to generate a resize event
with the correct window size when exiting fullscreen.
The roundtrip allows us to receive the configure callback that informs
us of the new window size before returning.
Fixes#6043
We really only care about DPI changes here, so this both reduces work and also avoids weird cases where viewport state can be corrupted by trivial window events. This doesn't _completely_ get rid of the issue but this is somewhat intentional, since apps will definitely want to do a full reset when changing displays anyhow (otherwise DPI/adapter changes will screw things up, and that's out of our control as long as both window size and drawable size are exposed at the same time.
Note that OpenGL still captures window events because of weird platform-specific issues like macOS and viewport stretching!
Fixes#5949
