[Intel-gfx] xdpyinfo gives wrong physical screen size

Felix Miata mrmazda at earthlink.net
Mon Jan 18 13:19:54 CET 2010

On 2010/01/18 06:24 (GMT-0500) dolphinling composed:

> xdpyinfo is giving the wrong physical screen size on my computer.

> The computer is an 845G running kernel, libdrm 2.4.17, xorg-server 
> 1.7.4, and xf86-video-intel from git.

> The monitor is an NEC MultiSync FE791SB (crt).

> The actual physical size (of the image, not sure about the glass) is 320x240 
> millimeters. The reported size is 423x318 millimeters. Since it is running at 
> 1600x1200 px, the actual resolution is 127 dpi, but the reported resolution is 
> 96 dpi.

> I'm sure there's more information I need to give for this to be solved, so just 
> tell me what it is and how to get it.

Some distros force DPI to 96. An example explanation why is at
http://wiki.mandriva.com/en/Font_Size_and_DPI while some DPI issues are
discussed at http://www.mozilla.org/unix/dpi.html

Not all distros use the same method to force DPI, so without knowing what
you're using the explanation to fix is also not known. For instance, one fix
might be to set an explicit DisplaySize in /etc/X11/xorg.conf, a file which
may otherwise be totally unnecessary in recent xorg versions. On Mandriva
2010.0 using xserver 1.6.4, Option "PreferredMode" "1600x1200" and
DisplaySize 338 253 permits 120 DPI on my i845G and Trinitron CRT. As noted
on the above Mozilla.org page, xdpyinfo may or may not report the actual DPI
used by apps, such as reported by Gecko on
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 Team OS/2 ** Reg. Linux User #211409

Felix Miata  ***  http://fm.no-ip.com/

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