Event processing in SDL - improvement ideas

[hrydgard]

Currently in SDL we do event polling in bursts each frame on the emulator main thread, which means that events will arrive in bursts at each "frame border" rather than asynchronously during gameplay. This likely is another cause of input lag, especially in 30hz games. #17685

Instead of polling for events every frame, we should just sit in a tight WaitEvent-loop, and have emulation and rendering happening on a different thread. This would be perfectly possible to implement with Vulkan and would be very similar to what we're doing on Windows.

However OpenGL comes with the complication that presentation has to happen on the same thread that created the context.

There does however seem to be workarounds that work:

https://skryabiin.wordpress.com/2015/04/25/hello-world/

But might simply not bother with improving lag with OpenGL for now.