Make stump-backlight work correctly on multiple monitors.

util/stump-backlight/README.org

@@ -22,12 +22,15 @@ stump-backlight exposes a few things:
 
 - The =*scale*= variable: defaults to 10. It defines the scale of the
   backlight. If you want more granularity than 10 steps, increase this variable.
-- The =*current-percent*= variable: defaults to 50. It defines the current
+- The =*default-percent*= variable: defaults to 50. It defines the default
   percentage of the backlight. Due to underlying technology issues, the
   percentage is managed separately from the real one, so this lets you set it at
   startup.
-- The =update= function: it takes the values from the variables and applies the
-  backlight.
+- The =(update output)= function: it takes the values from the variables and
+  applies the backlight. It takes one argument: the output (aka monitor) to
+  apply the update on.
+- The =(current-output)= function: it returns the output (aka monitor) of the
+  currently focused window. Useful to pass to the previous function.
 - 2 commands: =backlight-increase= and =backlight-decrease=. They increase or
   decrease based on the scale and apply the backlight.
 

util/stump-backlight/backlight.lisp

@@ -3,38 +3,48 @@
 (defvar *scale* 10
   "The backlight scale. Increase if you want more granularity.")
 
-(defvar *current-percent* 50
-  "CLX does not let us query the existing backlight, so we need to keep track of it.")
+(defvar *default-percent* 50
+  "Default value for an output's percentage.")
+
+(defvar *current-percent* (make-hash-table)
+  "CLX does not let us query the existing backlight, so we need to keep track of
+  it manually.")
+
+(defun current-output ()
+  (xlib:rr-get-output-primary (stumpwm:window-xwin (stumpwm:current-window))))
 
 (stumpwm:defcommand backlight-increase () ()
-  (when (< *current-percent* 100)
-    (setf *current-percent* (* (1+ (/ *current-percent* *scale*)) *scale*))
-    (update)))
+  (let* ((output (current-output))
+         (current-percent (or (gethash output *current-percent*) *default-percent*)))
+    (when (< current-percent 100)
+      (setf (gethash output *current-percent*) (* (1+ (/ current-percent *scale*)) *scale*))
+      (update output))))
 
 (stumpwm:defcommand backlight-decrease () ()
-  (when (> *current-percent* 0)
-    (setf *current-percent* (* (1- (/ *current-percent* *scale*)) *scale*))
-    (update)))
+  (let* ((output (current-output))
+         (current-percent (or (gethash output *current-percent*) *default-percent*)))
+    (when (> current-percent 0)
+      (setf (gethash output *current-percent*) (* (1- (/ current-percent *scale*)) *scale*))
+      (update output))))
 
-(defun update ()
-  (let* ((window (stumpwm:window-xwin (stumpwm:current-window)))
-         (output (xlib:rr-get-output-primary window))
-         (backlight-limits
-           (multiple-value-list
-            (xlib:rr-query-output-property stumpwm:*display* output :backlight)))
-         (backlight-type (xlib:rr-get-output-property stumpwm:*display* output :backlight)))
+(defun update (output)
+  (let ((backlight-limits
+          (multiple-value-list
+           (xlib:rr-query-output-property stumpwm:*display* output :backlight)))
+        (backlight-type (xlib:rr-get-output-property stumpwm:*display* output :backlight)))
     (destructuring-bind (min max) (fourth backlight-limits)
       (xlib:rr-change-output-property
        stumpwm:*display*
        output
        :backlight
        0 ; replace
-       (vector (scaled-current (1+ min) (1- max))) ; max is non-inclusive in X
-                                                   ; API, but inclusive in ours.
+       (vector (scaled-current output (1+ min) (1- max))) ; max is non-inclusive
+                                                          ; in X11 API, but
+                                                          ; inclusive in ours.
        backlight-type))))
 
-(defun scaled-current (min max)
-  (truncate (/ (* *current-percent* (- max min)) 100)))
+(defun scaled-current (output min max)
+  (truncate (/ (* (gethash output *current-percent*) (- max min)) 100)))
 
 ;; Opinionated but this one should be fair.
 (stumpwm:define-key stumpwm:*top-map*

util/stump-backlight/package.lisp

@@ -1,7 +1,8 @@
 (defpackage #:stump-backlight
   (:use #:cl)
-  (:export #:*current-percent*
+  (:export #:*default-percent*
            #:*scale*
            #:backlight-increase
            #:backlight-decrease
+           #:current-output
            #:update))