Use real display geometry on NS (bug#80331)

In nsfns.m, `x-display-mm-height' and `x-display-mm-weight' computes the
display size by dividing its (logical) pixel dimensions by 92 dpi.

This would often give wrong results: by default, logical pixels on in
macOS are computed to 72 dpi, but that can be changed by the user.

As macOS multi-screen geometry is all computed based on the main
screen's cooridnate system, use its dpi to compute the physical size of
the bounding box containing all the screens.

* src/nsfns.m (Fx_display_mm_height):
(Fx_display_mm_width): Calculate the total physical display size
using the main-screen's geometry.

Copyright-paperwork-exempt: yes

1 files changed, 24 insertions, 2 deletions

diff --git a/src/nsfns.m b/src/nsfns.m
index dddceb8d17b..cdd293b8c41 100644
--- a/src/nsfns.m
+++ b/src/nsfns.m
@@ -1995,9 +1995,20 @@ DEFUN ("x-display-mm-height", Fx_display_mm_height, Sx_display_mm_height, 0, 1,
        doc: /* SKIP: real doc in xfns.c.  */)
   (Lisp_Object terminal)
 {
+  double px_to_mm;
   struct ns_display_info *dpyinfo = check_ns_display_info (terminal);
 
-  return make_fixnum (ns_display_pixel_height (dpyinfo) / (92.0/25.4));
+#ifdef NS_IMPL_COCOA
+  CGDirectDisplayID did = CGMainDisplayID ();
+  CGSize size_mm = CGDisplayScreenSize (did);
+  CGRect bounds = CGDisplayBounds (did);
+
+  px_to_mm = size_mm.height / bounds.size.height;
+#else
+  dpi = 25.4 / dpyinfo->resx;
+#endif
+
+  return make_fixnum (ns_display_pixel_height (dpyinfo) * px_to_mm);
 }
 
 
@@ -2005,9 +2016,20 @@ DEFUN ("x-display-mm-width", Fx_display_mm_width, Sx_display_mm_width, 0, 1, 0,
        doc: /* SKIP: real doc in xfns.c.  */)
   (Lisp_Object terminal)
 {
+  double px_to_mm;
   struct ns_display_info *dpyinfo = check_ns_display_info (terminal);
 
-  return make_fixnum (ns_display_pixel_width (dpyinfo) / (92.0/25.4));
+#ifdef NS_IMPL_COCOA
+  CGDirectDisplayID did = CGMainDisplayID ();
+  CGSize size_mm = CGDisplayScreenSize (did);
+  CGRect bounds = CGDisplayBounds (did);
+
+  px_to_mm = size_mm.width / bounds.size.width;
+#else
+  px_to_mm = 25.4 / dpyinfo->resy;
+#endif
+
+  return make_fixnum (ns_display_pixel_width (dpyinfo) * px_to_mm);
 }