Hello Stefan,

Stefan Kangas <stefankangas@gmail.com> writes:

> Po Lu <luangruo@yahoo.com> writes:
>
>> The screen number should be the following part of the `display' frame
>> parameter:
>>
>>   1.1.1.1:0.5
>>             ^ screen number is 5
>>
>> if there is no period after the separator, then the screen number is 0.
>>
>> The currently active workspace can be obtained like so:
>>
>>   (x-window-property "_NET_CURRENT_DESKTOP" nil "CARDINAL" 0 nil t)
>>
>> if it fails by returning NULL, then you should fall back to:
>>
>>   (x-window-property "WIN_WORKSPACE" nil "CARDINAL" 0 nil t)
>>
>> and failing that, 0.
>>
>> The monitor name should also be easy to extract with
>> display-monitor-attributes-list, but if the source is anything other
>> than "XRandr", "XRandr 1.5" or "Gdk", you should fall back to using "0".
>
> Thanks, I've pushed a fix to master based on the above.  I very much
> appreciated the clear instructions above, which saved me a ton of time.
>
> I had to jump through extra hoops to get it to work also in the
> situation that Thierry described, however.  See commit b0289e7f6d and in
> particular bb9df76dc9.
>
> I installed XFCE on my machine to test the change and it works for me.
> If someone with XFCE could test that the change works for them, that
> would be welcome.

It is working fine on graphic display but on emacs -nw there is two problems:

1) The function wallpaper--format-arg is evaluating the format-specs each
time it is called and when display-graphic-p returns nil, user is
prompted for height and width at each call.

Here the xfce args:

("-c" "xfce4-desktop" "-p" "/backdrop/screen%S/monitor%M/workspace%W/last-image" "-s" "%f")

We are prompted for height and width for each of these args.

Here how you could fix this:

diff --git a/lisp/image/wallpaper.el b/lisp/image/wallpaper.el
index 36bc7e91a69..9ac0fd1dc91 100644
--- a/lisp/image/wallpaper.el
+++ b/lisp/image/wallpaper.el
@@ -374,8 +374,10 @@ See also `wallpaper-default-width'.")
 
 (defun wallpaper--get-height-or-width (desc fun default)
   (cond ((display-graphic-p) (funcall fun))
-        (noninteractive default)
-        ((read-number (format "Wallpaper %s in pixels: " desc) default))))
+        ;; (noninteractive default)
+        (t
+         (lambda ()
+           (read-number (format "Wallpaper %s in pixels: " desc) default)))))
 
 (autoload 'ffap-file-at-point "ffap")
 
@@ -444,7 +446,9 @@ This is the default function for `wallpaper-set-function'."
   (let* ((args (if (functionp wallpaper-command-args)
                    (funcall wallpaper-command-args)
                  wallpaper-command-args))
-         (real-args (mapcar (lambda (arg) (wallpaper--format-arg arg file))
+         (real-args (mapcar (lambda (arg)
+                              (let ((val (wallpaper--format-arg arg file)))
+                                (if (functionp val) (funcall val) val)))
                             args))
          (bufname (format " *wallpaper-%s*" (random)))
          (process

2) display-monitor-attributes-list doesn't return the value of monitor:

(display-monitor-attributes-list)

On graphic display it is ok:
=> (((name . "eDP")
  (geometry 0 0 1920 1080)
  (workarea 0 0 1920 1080)
  (mm-size 309 174)
  (frames #<frame  *Minibuf-1* - GNU Emacs at IPad-S340 0x55d6b2418828>)
  (source . "XRandr")))

But not on emacs -nw
=> (((geometry 0 0 238 57) (workarea 0 0 238 57) (mm-size nil nil) (frames #<frame F1 0x5636347dc460>)))

As a result the wallpaper is never set on emacs -nw.


-- 
Thierry