Problems with display-pixels-per-inch variable

[Kim F. Storm]

In the C code, we have this variable, which can be used by the
calculation of strech glyph width and height:

  DEFVAR_LISP ("display-pixels-per-inch",  &Vdisplay_pixels_per_inch,
    doc: /* Pixels per inch on current display.
Value is a number or a cons (WIDTH-DPI . HEIGHT-DPI).  */);
  Vdisplay_pixels_per_inch = make_float (72.0);


There are two problems with this:

1) It is a fixed value, so if it is not correct, the user
   must set it to the proper value  (possible, but not nice).

2) There is only one common value for all displays.


Re. 1, I would imagine that - at least for some setups - it is
possible to get the proper value from the X-Server or OS.

Does anyone know how to do that?


Re. 2, I guess the proper thing would be store this in the
display structure of each display, and use a function to set
the values for a specific display (if the values cannot be
determined automatically).

I can do item 2, but if someone would like to fix item 1, I would
appreciate if you would fix item 2 as well...

-- 
Kim F. Storm <address@hidden> http://www.cua.dk