Setting mouse speed in X (Shallow Thoughts)

Setting mouse speed in X

My mouse died recently: the middle button started bouncing, so a middle button click would show up as two clicks instead of one. What a piece of junk -- I only bought that Logitech some ten years ago! (Seriously, I'm pretty amazed how long it lasted, considering it wasn't anything fancy.)

I replaced it with another Logitech, which turned out to be quite difficult to find. Turns out most stores only sell cordless mice these days. Why would I want something that depends on batteries to use every day at my desktop?

But I finally found another basic corded Logitech mouse (at Office Depot). Brought it home and it worked fine, except that the speed was way too fast, much faster than my old mouse. So I needed to find out how to change mouse speed.

X11 has traditionally made it easy to change mouse acceleration, but that wasn't what I wanted. I like my mouse to be fairly linear, not slow to start then suddenly zippy. There's no X11 property for mouse speed; it turns out that to set mouse speed, you need to call it Deceleration.

But first, you need to get the ID for your mouse.

$ xinput list| grep -i mouse
⎜   ↳ Logitech USB Optical Mouse                id=11   [slave  pointer  (2)]

Armed with the ID of 11, we can find the current speed (deceleration) and its ID:

$ xinput list-props 11 | grep Deceleration
        Device Accel Constant Deceleration (259):       3.500000
        Device Accel Adaptive Deceleration (260):       1.000000

Constant deceleration is what I want to set, so I'll use that ID of 259 and set the new deceleration to 2:

$ xinput set-prop 11 259 2

That's fine for doing it once. But what if you want it to happen automatically when you start X? Those constants might all stay the same, but what if they don't?

So let's build a shell pipeline that should work even if the constants aren't.

First, let's get the mouse ID out of xinput list. We want to pull out the digits immediately following "id=", and nothing else.

$ xinput list | grep Mouse | sed 's/.*id=\([0-9]*\).*/\1/'
11

Save that in a variable (because we'll need to use it more than once) and feed it in to list-props to get the deceleration ID. Then use sed again, in the same way, to pull out just the thing in parentheses following "Deceleration":

$ mouseid=$(xinput list | grep Mouse | sed 's/.*id=\([0-9]*\).*/\1/')
$ xinput list-props $mouseid | grep 'Constant Deceleration'
        Device Accel Constant Deceleration (262):       2.000000
$ xinput list-props $mouseid | grep 'Constant Deceleration' | sed 's/.* Deceleration (\([0-9]*\)).*/\1/'
262

Whew! Now we have a way of getting both the mouse ID and the ID for the "Constant Deceleration" parameter, and we can pass them in to set-prop with our desired value (I'm using 2) tacked onto the end:

$ xinput set-prop $mouseid $(xinput list-props $mouseid | grep 'Constant Deceleration' | sed 's/.* Deceleration (\([0-9]*\)).*/\1/') 2

Add those two lines (setting the mouseid, then the final xinput line) wherever your window manager will run them when you start X. For me, using Openbox, they go in .config/openbox/autostart. And now my mouse will automatically be the speed I want it to be.