Check for focus before reading joypad input.

[zoltanvb]

Description

The udev and sdl joypad drivers were reading input in all cases. Now state is not monitored if window has no focus, connect / disconnect events are still processed.

Related Issues

Fixes #16261

[LibretroAdmin]

Is this how the other input drivers work as well? We wouldn't want to introduce something specific to certain input driver implementations in a non-unified way. Also I think it's the wrong approach to do this 'video_driver_has_focus()' call inside the input driver implementation, should be done higher-level.

Also in addition to it being a generic option that should work across the board for all input drivers, I feel this should remain entirely optional and tied behind a setting instead of forced, there might be usecases where we still want input for a non-focused window, this is in fact a handy feature when you want to still be able to play a game in an unfocused window with your gamepad.

[hizzlekizzle]

some people specifically request input detection in the background. it's a nasty surprise if you're not wanting, that, though, and end up wreaking havoc.

I'm loathe to add more options unnecessarily, but it might be worthwhile here.

[sonninnos]

In general I feel that Windows drivers do it correctly, which is: keyboard is ignored when app is not in focus, and controllers never.

[zoltanvb]

Udev keyboard/mouse does something similar already, but not much else.
Hm, it may be better to unify it, putting it behind an option may solve my concerns for a general solution - I wonder if video context driver focus (which is understood as keyboard focus on desktop) matches the user's perception of focus on all platforms.

[LibretroAdmin]

Ye I feel this should be behind a setting with the following options (you can decide on the names of each option)

0 - receives both keyboard and controller input when out of focus
1 - keyboard ignored when app is not in focus, but controller input still received
2 - keyboard and controller input ignored when app is not in focus

1 should be the default setting value.

[zoltanvb]

I'm fine with the approach (though option 0 will always be a bit misleading, as the possibility of getting keyboard input when out of focus is very much platform/driver dependent). I'm just wary of doing it centrally in input_driver.c, which is probably the 3rd most complex piece in whole RA I have visited so far, so it may take a while. I can close the PR until that time, if preferred.