From: 	Dan Berger <dberger _at_ oubliette _dot_ org>
To: 	keithp _at_ keithp _dot_ com
Cc: 	agd5f _at_ yahoo _dot_ com
Subject: 	xrandr dpi question
Date: 	Fri, 28 May 2004 13:25:22 -0700
Mailer: 	Ximian Evolution 1.5.6 (1.5.6-04192004) 	

Greetings.  Sorry for the email out of the blue, I've done a fair bit of
googling to see if this is question has been asked and answered, but
come up blank.

I'm curious about a behavior I'm observing when using XrandR to change
resolutions.  I'm using a notebook with a radeon chip, and the
"MergedFB" driver modifications by Alex Deucher (who I've cc'd on this
message).  (On the off-chance MergedFB doesn't ring any bells, it's
essentially a single frame-buffer spanning both card outputs, aka
TwinView in nvidia-speak).  

When I have an external monitor attached I want to run in 2048x768
(spanning the LCD and external monitor), and when I'm using only the
LCD, I want 1024x768.

xrandr does this, but I've seen some strange behavior in some
applications - especially emacs, ghostview, and openoffice.  I've
narrowed it down to the fact that xrandr is changing the dpi settings
for the X server - and I'm wondering why this is the right thing to do.

The "default" X mode is 2048x768, and xdpyinfo reports:

resolution: 75x75 dots per inch

if I xrandr to 1024x768, and re-run xpdyinfo, it reports

resolution: 35x75 dots per inch

Many applications aren't affected (those based on GTK, for example, seem
immune) but not being an X hacker, it's not obvious why this dpi
adjustment is, in general, the right thing to do.  I'm guessing that it
has to do with the fact that in the MergedFB case the physical
dimensions of the "screen" are changing - but xrandr doesn't realize
that.  (I also figured it might be a driver problem, which is part of
why I'm cc'ing Alex.)

If you'd be so kind, I'd appreciate any thoughts you have on the
subject.

Cheers.

--- Response ---

From: 	Keith Packard <keithp _at_ keithp _dot_ com>
To: 	Dan Berger <dberger _at_ oubliette _dot_ org>
Cc: 	keithp _at_ keithp _dot_ com, agd5f _at_ yahoo _at_ com
Subject: 	Re: xrandr dpi question
Date: 	Fri, 28 May 2004 13:28:10 -0700
Mailer: 	exmh version 2.3.1 11/28/2001 with nmh-1.1


Around 13 o'clock on May 28, Dan Berger wrote:

> it's not obvious why this dpi
> adjustment is, in general, the right thing to do.

It isn't; it's just a bug in the XFree86 DDX implementation of Xrandr.

-keith