May 15, 2016

Debounce bogus repeated mouse clicks in Xorg with xbindkeys

My current Razer E-Blue mouse had this issue since I've got it - Mouse-2 / BTN_MIDDLE / middle-click (useful mostly as "open new tab" in browsers and "paste" in X) sometimes produces two click events (in rapid succession) instead of one.

It was more rare before, but lately it feels like it's harder to make it click once than twice.

Seem to be either hardware problem with debouncing circuitry or logic in the controller, or maybe a button itself not mashing switch contacts against each other hard enough... or soft enough (i.e. non-elastic), actually, given that they shouldn't "bounce" against each other.

Since there's no need to double-click that wheel-button ever, it looks rather easy to debounce the click on Xorg input level, by ignoring repeated button up/down events after producing the first full "click".

Easiest solution of that kind that I've found was to use guile (scheme) script with xbindkeys tool to keep that click-state data and perform clicks selectively, using xdotool:

(define razer-delay-min 0.2)
(define razer-wait-max 0.5)
(define razer-ts-start #f)
(define razer-ts-done #f)
(define razer-debug #f)

(define (mono-time)
  "Return monotonic timestamp in seconds as real."
  (+ 0.0 (/ (get-internal-real-time) internal-time-units-per-second)))

(xbindkey-function '("b:8") (lambda ()
  (let ((ts (mono-time)))
      ;; Enforce min ts diff between "done" and "start" of the next one
      (or (not razer-ts-done) (>= (- ts razer-ts-done) razer-delay-min))
      (set! razer-ts-start ts)))))

(xbindkey-function '(Release "b:8") (lambda ()
  (let ((ts (mono-time)))
    (when razer-debug
      (format #t "razer: ~a/~a delay=~a[~a] wait=~a[~a]\n"
        razer-ts-start razer-ts-done
        (and razer-ts-done (- ts razer-ts-done)) razer-delay-min
        (and razer-ts-start (- ts razer-ts-start)) razer-wait-max))
        ;; Enforce min ts diff between previous "done" and this one
        (or (not razer-ts-done) (>= (- ts razer-ts-done) razer-delay-min))
        ;; Enforce max "click" wait time
        (and razer-ts-start (<= (- ts razer-ts-start) razer-wait-max)))
      (set! razer-ts-done ts)
      (when razer-debug (format #t "razer: --- click!\n"))
      (run-command "xdotool click 2")))))

Note that xbindkeys actually grabs "b:8" here, which is a "mouse button 8", as if it was "b:2", then "xdotool click 2" command will recurse into same code, so wheel-clicker should be bound to button 8 in X for that to work.

Rebinding buttons in X is trivial to do on-the-fly, using standard "xinput" tool - e.g. xinput set-button-map "My Mouse" 1 8 3 (xinitrc.input script can be used as an extended example).

Running "xdotool" to do actual clicks at the end seem a bit wasteful, as xbindkeys already hooks into similar functionality, but unfortunately there's no "send input event" calls exported to guile scripts (as of 1.8.6, at least).

Still, works well enough as it is, fixing that rather annoying issue.

[xbindkeysrc.scm on github]

Member of The Internet Defense League