Re: Child-frame can not move to proper position when run "env GDK_SCALE=2 emacs"

[Robert Pluim <rpluim@gmail.com>]

"Feng Shu" <tumashu@163.com> writes:

> martin rudalics <rudalics@gmx.at> writes:
>
>>> When I run "env GDK_SCALE=2 emacs", the below code can not work properly
>>>
>>> ```
>>> (let ((test (let ((after-make-frame-functions nil))
>>>                (make-frame
>>>                 `((parent-frame . ,(window-frame))
>>>                   (width . 50)
>>>                   (height . 1)))))
>>>        (pos (posn-x-y (posn-at-point (point) (selected-window)))))
>>>    (set-frame-position test (car pos) (cdr pos)))<I>
>>> ```
>>>
>>> When I eval the code at the <I>, the new created frame can not move to
>>> <I>, it move to the wrong position.
>>
>> What happens when you divide the pos values by two?
>
> When (/ x 2) and (/ y 2), It works! :-)
>
>>
>> We do not expose the GTK/GDK scale values in Lisp, maybe we should.
>> Robert any ideas?

Ugh. I don't think we should expose the scale values, we should fix
whatever the issue is with set-frame-position. Naively that's the
attached patch, but I worry about other places that assume unscaled
coordinates. I'll run with it for a while and see if any pop up.

Longer term we need to implement your 'eliminate direct X calls' plan,
and have everything inside Emacs use GTK coordinates.

Robert

diff --git i/src/xterm.c w/src/xterm.c
index f771631daf..950e6231e0 100644
--- i/src/xterm.c
+++ w/src/xterm.c
@@ -10311,6 +10311,14 @@ x_set_offset (struct frame *f, register int xoff, register int yoff, int change_
 {
   int modified_top, modified_left;
 
+#ifdef USE_GTK
+  {
+    int scale = xg_get_scale(f);
+    xoff /= scale;
+    yoff /= scale;
+  }
+#endif
+
   if (change_gravity > 0)
     {
       f->top_pos = yoff;