display-mm-width return value off on Windows

[Ralf Angeli <angeli@caeruleus.net>]

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On Windows the return values of `display-mm-width' and
`display-mm-height' don't really reflect the screen width and height
in millimeters.  I attached a patch which yields more realistic
results.

In my case:

                   display-mm-*   display-mm-*
        Real size  without patch  with patch
Width   285mm      370            279
Height  215mm      277            203

For a preview-latex user who originally reported the problem:

                   display-mm-*   display-mm-*
        Real size  without patch  with patch
Width   330mm      320            305
Height  207mm      240            203

The original report described that images generated by preview-latex
(which uses `display-mm-{width,height}' for that matter) are distorted
horizontally (see bug report at
<URL:http://permalink.gmane.org/gmane.emacs.auctex.bugs/673>).  In my
case these images were too small compared to the font size (see bug
report with screenshot at
<URL:http://permalink.gmane.org/gmane.emacs.auctex.bugs/449>).  With
the patch applied both of these problems get better.

-- 
Ralf

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Index: w32fns.c
===================================================================
RCS file: /sources/emacs/emacs/src/w32fns.c,v
retrieving revision 1.271
diff -c -r1.271 w32fns.c
--- w32fns.c	30 Jun 2006 13:40:21 -0000	1.271
+++ w32fns.c	6 Jul 2006 17:47:53 -0000
@@ -6502,15 +6502,16 @@
 {
   struct w32_display_info *dpyinfo = check_x_display_info (display);
   HDC hdc;
-  int cap;
+  int height;
 
   hdc = GetDC (dpyinfo->root_window);
 
-  cap = GetDeviceCaps (hdc, VERTSIZE);
+  height = round (GetDeviceCaps (hdc, VERTRES)
+		  / GetDeviceCaps (hdc, LOGPIXELSY) * 25.4);
 
   ReleaseDC (dpyinfo->root_window, hdc);
 
-  return make_number (cap);
+  return make_number (height);
 }
 
 DEFUN ("x-display-mm-width", Fx_display_mm_width, Sx_display_mm_width, 0, 1, 0,
@@ -6524,15 +6525,16 @@
   struct w32_display_info *dpyinfo = check_x_display_info (display);
 
   HDC hdc;
-  int cap;
+  int width;
 
   hdc = GetDC (dpyinfo->root_window);
 
-  cap = GetDeviceCaps (hdc, HORZSIZE);
+  width = round (GetDeviceCaps (hdc, HORZRES)
+		 / GetDeviceCaps (hdc, LOGPIXELSX) * 25.4);
 
   ReleaseDC (dpyinfo->root_window, hdc);
 
-  return make_number (cap);
+  return make_number (width);
 }
 
 DEFUN ("x-display-backing-store", Fx_display_backing_store,

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