From: John Stone (
Date: Thu Mar 29 2012 - 10:20:27 CDT

Hi Christoph,
  I understand why you find this behavior confusing, it is related to
backwards compatibility with the original IRIS GL versions of VMD
and the coordinate system that IRIS GL used when positioning windows
on the display. I plan to eradicate the IRIS GL compatability
(and the resultant confusion) in a future rev of VMD along with many
other old interfaces that no longer need to remain backwards compatible
any more.

The difference between IRIS GL and other coordinate systems is that
IRIS GL had Y increasing from the lower edge of the screen rather than
down from the top. So, if you take the screen resolution and subtract off
the X11 Y coordinate, you'll get the "IRIS GL" version of the Y coordinate
that VMD expects. So, if your screen was 1920x1080, you'd do something
like this:
  vmd -pos 1 1080

With VMD running you can do essentially the same thing like this at the
VMD text console:
  display reposition 0 1080


On Wed, Mar 28, 2012 at 09:17:10AM +1000, Christoph Willing wrote:
> I'm working on running vmd on a tiled display cluster - running
> multiple instances of vmd (1 for each display) and synchronising them
> with vmdcollab. I need to run each vmd instance at the full size of
> the screen, positioned at (0,0) however this is not allowed - (1,0) is
> OK, in fact just about any other positive values for x & y work as
> expected.
> This behaviour can be confirmed by observing the difference between
> running:
> vmd -pos 0 0
> and
> vmd -pos 1 0
> I think this may be a bug - in line 248 of src/VMDAPp.C, I see:
> int *dloc = (displayLoc[0] > 0 ? displayLoc : (int *) NULL);
> which disallows x being 0. Shouldn't that be:
> int *dloc = (displayLoc[0] >= 0 ? displayLoc : (int *) NULL);
> chris
> Christoph Willing +61 7 3365 8316
> Research Computing Centre
> University of Queensland

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