screen physical size, DPI, font size - how does it work?

Alexej Davidov alexej.davidov at
Sun Oct 7 07:04:52 PDT 2007

On Sun, 7 Oct 2007 14:54:35 +0200
Arkadiusz Miskiewicz <arekm at> wrote:

> On Sunday 07 of October 2007, Alexej Davidov wrote:
> > Hi,
> >
> > up to now I've set the DPI value explicitely with --dpi 100. This
> > gives sensible font sizes. I've now tried to let X do it
> > automatically, but with no success. The detected physical screen
> > size is wrong and I didn't manage to convince X of the correct one.
> > So I always get 96x96 dpi. Also I don't really understand How the
> > DPI value given in Xorg.log correlates to the actually set value.
> >
> > I use the ati driver on a R300 (version 6.7.195) with xorg-core 1.4
> > on an IBM Thinkpad.
> Do you have "Unknown DDCType 6 found" in x log? If yes then look at
> and 

No I haven't.

> Note that there is second bug in xorg 1.4 for randr 1.2 drivers where
> you can't override panel size with DisplaySize in config.

Ah, OK. Anyway, it seems that it is not desirable to set the
theoretically correct dpi value, as then the fonts get awfully big. I
don't understand the rational behind this, though.


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