Tuesday, January 09, 2018

Arcade Sticks and MAME and Key Events, Oh My

This is a solution so simple I feel very silly for not thinking of it sooner.

from a virtual console: (as in ctrl+alt+f1 etc)
    xinit /usr/games/mame -- :1

So my actual problem, for anyone who's curious, is that while using MAME to play some arcade games, my window manager (spectrwm) was capturing the "Alt" key (player 1's second button by default) and doing whatever actions alt+this and alt+that were bound to, depending on what other buttons (keys) were being pressed.

"Just remap the buttons" is a common answer, and not a bad one in many situations.  But the keyboard I use when playing arcade games is this big ol' thing:
It looks and feels like and is in fact built from arcade joystick hardware, but for maximum compatibility it acts like a keyboard when plugged into a computer.  It does indeed support remapping its "keys", but I'm running linux for cripe's sake, there had to be a better way.

I started down this logical path:  VirtualBox (virtual machine container; think VMware but open) steals the entire keyboard so that Alt and other modifier keys end up going to the virtual machines it runs, rather than the host.  Now and then, I get trapped on a certain screen for a moment because I can't just alt+number my way to another one.  It's a mildly annoying but useful feature.  MAME, the software I use to run old arcade games, doesn't seem to have any such option, but it really ought to.

VirtualBox and MAME are both open, so I could dive into the code and see how the keyboard grabbing is done in the former, and possibly graft it into the latter.  I imagine the abstractions used in each case are quite different, but I bet given time I (or someone) could figure it out without too much hassle.

But if I'm going to dive into code, maybe there was something simpler I could do.  Spectrwm, my window manager, is tiny compared to VirtualBox or MAME.  It does almost nothing, which is why I like it.  One of the things it does manage is the ability to assign special behaviour to certain programs.  (It calls these special cases "quirks".)  Perhaps I could dig in there and have it ignore all hotkeys when a certain program (mame) is active.

Then it hit me, again, that I'm running linux, for cripe's sake.  Just because I'm using spectrwm on my X server doesn't mean I can't run another X server with no window manager at all.  And sure enough, if I fire up a second instance of X thusly:
    xinit /usr/games/mame -- :1
...then I have a completely isolated X running only MAME, and can switch between it and my main X session anytime.  For me, this is the best of all worlds.  I can keep up spectrwm and mame updated without having to manage any local patches, and I can mash any combination of those big joystick buttons without any unintended behaviour.

Some keyword search phrases, for any future schmucks having similar trouble:
  • mame grab alt key
  • mame spectrwm keys
  • mame window manager keys
  • wrap x keyboard events
  • linux x grab all keys
  • mame grab keys like virtualbox

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