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1. virtual x360 pad [ViGEmBus provider] should work too.
2. ~most usb keyboards are limited to physically hold up to 4-6 buttons simultaneously [and the question is "are Midi keyboards the most effective/unlimited to play with 10 fingers? 4 arms?]
3. it will be possible for 2 players to play using only 1 keyboard and 4 players using 2 keyboards with "rules in mind" - "one hit + one direction",
and good mapping, which not only will cover "wasd" - will involve diagonals [to free the need of holding 3 buttons]
for racing games rules are "don't shoot/use_items while drift", "one type of break at time", etc.
[in your case 2 players having 2 keyboards do not need such rules and are able to play fully]
4. DirectInput gamepads can be configured to use 128 buttons [vJoy] [this is enough to make a good use of ppsspp's "multiple buttons meaning one psp button" and analog limiter]
1. virtual x360 pad [ViGEmBus provider] should work too.
2. ~most usb keyboards are limited to physically hold up to 4-6 buttons simultaneously [and the question is "are Midi keyboards the most effective/unlimited to play with 10 fingers? 4 arms?]
3. it will be possible for 2 players to play using only 1 keyboard and 4 players using 2 keyboards with "rules in mind" - "one hit + one direction",
and good mapping, which not only will cover "wasd" - will involve diagonals [to free the need of holding 3 buttons]
for racing games rules are "don't shoot/use_items while drift", "one type of break at time", etc.
[in your case 2 players having 2 keyboards do not need such rules and are able to play fully]
4. DirectInput gamepads can be configured to use 128 buttons [vJoy] [this is enough to make a good use of ppsspp's "multiple buttons meaning one psp button" and analog limiter]