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

[Ralf Angeli <angeli@caeruleus.net>]

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* Eli Zaretskii (2006-07-09) writes:

>> From: Ralf Angeli <angeli@caeruleus.net>
>> 
>> If `GetDeviceCaps (hdc, HORSIZE)' always assumes a fixed DPI value
>> that would explain why the values are so inaccurate especially on
>> displays with a high DPI value.  In that case I think it makes sense
>> to use the DPI value when calculating the size (as my patch does) and
>> assume that the user set it to a value matching her monitor.
>> 
>> As a last resort we could provide user options (in Emacs) for setting
>> the correct size of the screen which will be used as return values for
>> `display-mm-{width,height}'.
>
> Sounds like a good plan to me.

Here are change log entries and patches to achieve that:

2006-07-11  Ralf Angeli  <angeli@caeruleus.net>

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


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Index: frame.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/frame.el,v
retrieving revision 1.236
diff -u -r1.236 frame.el
--- frame.el	25 Mar 2006 07:40:18 -0000	1.236
+++ frame.el	11 Jul 2006 18:40:03 -0000
@@ -1081,17 +1081,35 @@
      (t
       (frame-width (if (framep display) display (selected-frame)))))))
 
+(defcustom display-mm-height nil
+  "Height of display in millimeters.
+If non-nil, used as return value for function `display-mm-height'."
+  :version "22.1"
+  :type 'integer
+  :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)))
+If the information is unavailable, value is nil.  Return value of
+variable `display-mm-height' if set."
+  (or display-mm-height
+      (and (memq (framep-on-display display) '(x w32 mac))
+	   (x-display-mm-height display))))
+
+(defcustom display-mm-width nil
+  "Width of display in millimeters.
+If non-nil, used as return value for function `display-mm-width'."
+  :version "22.1"
+  :type 'integer
+  :group 'frames)
 
 (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)))
+If the information is unavailable, value is nil.  Return value of
+variable `display-mm-width' if set."
+  (or display-mm-width
+      (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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2006-07-11  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 1.271
diff -u -r1.271 w32fns.c
--- w32fns.c	30 Jun 2006 13:40:21 -0000	1.271
+++ w32fns.c	11 Jul 2006 18:38:37 -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 (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,
@@ -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 (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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-- 
Ralf

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