SDL2 does not support changing display resolutions independently of an
SDL window. As a workaround, if the user uses ChangeResolution and then
makes a GameWindow fullscreen, we use old-style SDL fullscreen which
changes the resolution. If the user makes a GameWindow fullscreen
without calling ChangeResolution first, we use the new
fullscreen-desktop mode to match the other OpenTK backends.
This is a new platform that can be used then sdl2 is installed on the target system. SDL2 is commercially supported by Valve and provides better support for MacOS compared to our current implementation (Cocoa vs Carbon). It will also help us introduce faster support for new platforms. Existing platforms remain as a fallback and will be automatically used if sdl2 is not installed.
Please note that this is still a work in progress. The new mouse and keyboard API is not supported yet. Due to limitations of sdl2, multiple mice/keyboards are also not supported.
