This commit enables Rebirth to build with SDL2, but the result is not
perfect.
- SDL2 removed some sticky key support. Rebirth may behave differently
now in this area.
- SDL2 removed some key-repeat related support. Rebirth may behave
differently now in this area.
- SDL2 gained the ability to make a window fullscreen by sizing it to
the desktop instead of by changing the desktop resolution. Rebirth
uses this, and it mostly works.
- Resizing while in the automap does not notify the automap code, so
the view is wrong until the player switches out of automap mode and
back in.
- SDL2 changed how to enumerate available resolutions. Since
fitting the window to the desktop is generally more useful than
fitting the desktop to the window, I chose to drop support for
enumerating resolutions instead of porting to the new API. Users can
now enter an arbitrary window dimension and Rebirth will make an
attempt to use it.
- It might be useful to cap the window dimension at the desktop
dimension, but that is not done yet.
- Entering fullscreen mode through the Controls->Graphics submenu
failed to notify the relevant subsystems, causing the rendered
content not to rescale. For now, compile out the option to toggle
full screen through that menu. Toggling through Alt+Enter works
properly.
Despite these quirks, this is a substantial improvement over the prior
commit, where SDL2 cannot be used at all. The remaining issues can be
resolved in future work.
References: <https://github.com/dxx-rebirth/dxx-rebirth/issues/82>
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