Tracking issue for changes/fixes in latest SDL version

[Susko3]

Fixed by libsdl-org/SDL@6c96217:

• Mouse position is changed upon alt-tabbing in fullscreen mode #4159
• Mouse moves to the corner of the screen when alt+tab osu#12228
• Cursor stuck top left when leaving game when it's fullscreen & raw input #4050 (probably fixed by something else)
• Fix cursor warping to center of screen when alt-tabbing in fullscreen #5136

Fixed by libsdl-org/SDL@5ff4243:

• Held mouse buttons aren't updated when the cursor is outside of the window #4055
• relevant: OS cursor is invisible while dragging #1679
• SDL no longer sends SDL_WINDOWEVENT_ENTER and SDL_WINDOWEVENT_LEAVE events if any button is pressed when the mouse leaves and enters the window. This introduces a nasty bug with MouseHandler where relative mode won't be re-enabled if the mouse leaves and enters the window while holding down any buttons. This is by design.
• Enable SDL_HINT_MOUSE_AUTO_CAPTURE when not using relative mode #5163

Fixed by libsdl-org/SDL#5398:

• Pressing Enter key during IME composition may send message directly osu#17231
• This PR introduces a bug with our IME handling, as SDL will now send multiple SDL_TextInputEvents when the text is longer than 32 characters. Should be easy to fix, either delay resetting of recentImeResult, or match the SDL text with our composition text using string.Contains.
• Properly block SDL IME results sent as multiple text events + upstream SDL fixes #5141
• update ResetIme to use SDL_ClearComposition on non-windows platforms.

General:

• Reach out to users affected by Alt-tab while in exclusive fullscreen takes longer than expected osu#17381 and check if it's fixed.

Things to note

https://github.com/flibitijibibo/SDL2-CS is not updated to the latest SDL, and there is no open PR on their side. We can set the hints, but we won't be able to use SDL_ClearComposition.

[Susko3]

With the three PRs, we should be ready for an SDL bump. SDL2-CS was also recently bumped to 2.0.22. Making use of new APIs, such as SDL_ClearComposition(), can be added later.

We may want for libsdl-org/SDL#5572 to be fixed, as noticed on discord.

[peppy]

I'll look to do a bump today or tomorrow if no one else beats me

[peppy]

@Susko3 1.0.518-alpha is now propagating to nuget. I'll leave it in your hands to consume it in the order of your choosing.