Fix Proced display header alignment under 'text-scale-adjust'

* lisp/proced.el (proced-mode): Force the header-line to scale
according to 'text-scale-adjust'.
(proced-header-line): Use width of the header-line's face's
characters as align-to units, not the width of the frame's
default face's font.  (Bug#64752)

* src/xdisp.c (calc_pixel_width_or_height): Use font's
average_width or space_width, not max_width, as the correct
measure of the font's width.  This is consistent with the rest of
the display engine.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index da6e0afa8e1..2eba42e3d90 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -29093,7 +29093,9 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       /* 'width': the width of FONT.  */
       if (EQ (prop, Qwidth))
         return OK_PIXELS (font
-                          ? FONT_WIDTH (font)
+                          ? (font->average_width
+                             ? font->average_width
+                             : font->space_width)
                           : FRAME_COLUMN_WIDTH (it->f));
 #else
       if (EQ (prop, Qheight) || EQ (prop, Qwidth))