Re: display-mm-width return value off on Windows

[Ralf Angeli <angeli@caeruleus.net>]

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* Ralf Angeli (2006-07-06) writes:

> On Windows the return values of `display-mm-width' and
> `display-mm-height' don't really reflect the screen width and height
> in millimeters.

Meanwhile we got another bug report on the AUCTeX list related to this
issue.

I provided a patch for w32fns.c the majority of developers were in
favor of but which hasn't been checked into CVS and a patch for
frame.el about which I haven't got feedback.  I am adding them to this
mail again with updated change log entries for reference:

2006-08-05  Ralf Angeli  <angeli@caeruleus.net>

	* w32fns.c (Fx_display_mm_height, Fx_display_mm_width): Calculate
	size of display by means of size in pixels and number of pixels
	per inch.


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Index: w32fns.c
===================================================================
RCS file: /sources/emacs/emacs/src/w32fns.c,v
retrieving revision 1.275
diff -u -r1.275 w32fns.c
--- w32fns.c	4 Aug 2006 17:21:21 -0000	1.275
+++ w32fns.c	5 Aug 2006 14:37:37 -0000
@@ -6537,15 +6537,16 @@
 {
   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 (25.4 * GetDeviceCaps (hdc, VERTRES)
+		  / GetDeviceCaps (hdc, LOGPIXELSY));
 
   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,
@@ -6559,15 +6560,16 @@
   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 (25.4 * GetDeviceCaps (hdc, HORZRES)
+		 / GetDeviceCaps (hdc, LOGPIXELSX));
 
   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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2006-08-05  Ralf Angeli  <angeli@caeruleus.net>

	* frame.el (display-mm-dimensions-alist): New variable.
	(display-mm-height, display-mm-width): Use it.


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Index: frame.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/frame.el,v
retrieving revision 1.237
diff -u -r1.237 frame.el
--- frame.el	21 Jul 2006 07:42:52 -0000	1.237
+++ frame.el	5 Aug 2006 14:36:20 -0000
@@ -1083,17 +1083,35 @@
      (t
       (frame-width (if (framep display) display (selected-frame)))))))
 
+(defcustom display-mm-dimensions-alist nil
+  "Alist for specifying screen dimensions in millimeters.
+Each element of the alist has the form (display . (width . height)),
+e.g. (\":0.0\" . (287 . 215)).
+
+The dimensions will be used for `display-mm-height' and
+`display-mm-width' if defined for the respective display."
+  :version "22.1"
+  :type '(alist :key-type (string :tag "Display")
+		:value-type (cons :tag "Dimensions"
+				  (integer :tag "Width")
+				  (integer :tag "Height")))
+  :group 'frames)
+
 (defun display-mm-height (&optional display)
   "Return the height of DISPLAY's screen in millimeters.
 If the information is unavailable, value is nil."
-  (and (memq (framep-on-display display) '(x w32 mac))
-       (x-display-mm-height display)))
+  (or (cddr (assoc (or display (frame-parameter nil 'display))
+		   display-mm-dimensions-alist))
+      (and (memq (framep-on-display display) '(x w32 mac))
+	   (x-display-mm-height display))))
 
 (defun display-mm-width (&optional display)
   "Return the width of DISPLAY's screen in millimeters.
 If the information is unavailable, value is nil."
-  (and (memq (framep-on-display display) '(x w32 mac))
-       (x-display-mm-width display)))
+  (or (cadr (assoc (or display (frame-parameter nil 'display))
+		   display-mm-dimensions-alist))
+      (and (memq (framep-on-display display) '(x w32 mac))
+	   (x-display-mm-width display))))
 
 (defun display-backing-store (&optional display)
   "Return the backing store capability of DISPLAY's screen.

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Could somebody please apply at least one of them or tell me what to
change in order for them to get accepted?  I am planning to upload a
new precompiled version of Emacs for Windows to alpha.gnu.org once
this is settled.

-- 
Ralf

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