DisplaySize and X and DPI

mcr at xdsinc.net mcr at xdsinc.net
Tue Sep 25 14:47:55 PDT 2007

Hash: SHA1

>>>>> "Nicolas" == Nicolas Mailhot <nicolas.mailhot at laposte.net> writes:
    >> https://bugs.launchpad.net/ubuntu/+source/libgnome/+bug/118745

    Nicolas> X will never be 100% fixed, sometimes the hardware just does not send
    Nicolas> any correct size info. GNOME needs to learn to prompt the user for
    Nicolas> DisplaySize in that case (*not* dpi as users do not know WTF dpi is
    Nicolas> and that only leads to dpi abuse).

    Nicolas> I wonder if the fact X didn't get a good DisplaySize and fell-back on
    Nicolas> a hardcoded size is exposed to other apps?

  (working on XRANDR patches for Xvnc4. I hope to post patches against
1.2.0 that build cleanly by the end of next week, and I will work again
on making it work with 1.4.0 soonish)

  I think that the situation is twofold, 
    a) X/video "hardware"/etc. doesn't actually know what the
       DisplaySize *is*, and should say "0" or unknown.
       I don't think this happens very often, unfortunately.

    b) X thinks it knows, and reports a value, but has no way to know
       that it is wrong.

  Case (a) is easy to detect and it's obvious that you have to prompt
the user.  Case (b) is harder, and in the context of VNC (and XDP), the
physical screen (and size) can change without X being aware of it. 
  We haven't come up with a solution yet, and we know that changing
ought to cause all applications to pick new fonts, but that this is
going to be a PITA.

  I haven't looked deeply into randr 1.2, but I see that the palette of
resolutions is gone, which is great.  I didn't see if the display X/Ymm
was settable seperately from the X/Y resolution. Is it?

- -- 
Michael Richardson <mcr at xdsinc.net>
XDS Inc, Ottawa, ON             
Personal: http://www.sandelman.ca/mcr/ 

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