Hack and / - Lightning Hacks

One of the more interesting parts of any conference is the lightning talks. If you haven't experienced one, a lightning talk typically features a number of different speakers, each giving a short (5–20 minutes) presentation. Lightning talks take advantage of the fact that often a speaker has an interesting topic to present, but the topic won't fill an entire hour time slot. So, lightning talks round up each of these speakers one after the other in the same time slot. Because of the variety of information and the fast nature of lightning talks, they can be really informative, interesting and definitely fun.

As I was considering what topic to cover for this month's column, I realized I had a number of different hacks I'd like to mention, but none that could really fill a full column. In the spirit of lightning talks, I decided to put all of these hacks together in true rapid-fire fashion.

In the March 2008 issue of Linux Journal, I introduced the wmctrl tool and discussed how to use it to move, resize, shade and do all sorts of window management tasks from the command line. I also introduced a few scripts I had written and bound to keys to resize and shade a few different windows on my desktop. Near the end of that article, I mentioned:

Well, shortly after I wrote that, I completed my reset script. This script goes from desktop to desktop (or because I use Compiz, viewport to viewport) and moves and resizes windows per my specifications. I've added comments to explain particular sections:

#!/bin/sh

# First save my current viewport so I can return 
# to it after I'm done
SAVED_VP=`wmctrl -d | perl -ne '/VP: (\d+,\d+)/; print $1;'`

# Then, move to the first viewport (at 0,0). Because it 
# can take a second or two for this to take effect, 
# I've opted to create a while loop that will
# continue to attempt to switch to that viewport 
# until it detects it is actually there.
VP=0,0
while [ `wmctrl -d | perl -ne '/VP: (\d+,\d+)/; 
 ↪print $1;'` != $VP ];
do
    wmctrl -o $VP
done

# Now resize, move, and change state of particular 
# windows (see the wmctrl man page, or my wmctrl 
# column for more information on the options).
wmctrl -r 'Eterm Main 1' -e '0,0,0,645,420'
wmctrl -r 'Irssi Term' -e '0,469,0,810,500'
wmctrl -r 'Irssi Term' -b add,shaded
wmctrl -r 'Irssi Term' -b add,below
wmctrl -r 'gkrellm' -b add,sticky
wmctrl -r "Irssi Notify Term" -e '0,1180,550,100,230'

# I now switch to the second viewport. As my screen 
# is 1280x768, the second viewport is at 1280,0. 
# If I wasn't sure, I could switch to that viewport
# and check the output of wmctrl -d for the proper coordinates.
VP=1280,0
while [ `wmctrl -d | perl -ne '/VP: (\d+,\d+)/; 
 ↪print $1;'` != $VP ];
do
    wmctrl -o $VP
done

wmctrl -r "Mozilla Firefox" -e '0,5,0,1040,708'

# Finally I switch back to my original viewport 
# so I'm back where I started.
wmctrl -o $SAVED_VP

Although there are certainly a lot of commands in that script, it actually didn't take long to write. Most of the script is simply one wmctrl command after another, and I spent a majority of the time actually fine-tuning the locations of each window and figuring out the best way to switch viewports. If your desktop environment uses multiple desktops instead of one desktop with multiple viewports, you would use the -s option to change desktops instead of the -o option, which is used for viewports. You also would need to change the logic in the while loop to something more like:

DESKTOP=1
while [ `wmctrl -d | perl -ne '/^(\d+).*?\*/; 
 ↪print $1;'` != $DESKTOP ];
do
    wmctrl -s $DESKTOP
done

Although I normally use my laptop with its own built-in screen, I frequently give presentations, so I need to display on both the LCD and the external VGA connector. Unfortunately, my laptop's function keys to toggle between those states don't currently work in Linux, so I've had to put it into a script paired with a keybinding.

The xrandr program works great with my laptop to toggle between displays, so my script first examines the output of xrandr to see whether the VGA port is connected, and if so, it adds it as a display. Otherwise, it disables VGA. I also added a line to echo some text to osd_cat. I installed this program so that I would get some output on the screen to let me know which mode my script had chosen. When I'm ready to output to a projector, I just connect it to my laptop and run the script. When I'm finished with the presentation, I disconnect it and run the script again:

#!/bin/sh

if xrandr | grep -q 'VGA connected'; then
    echo "LVDS + VGA" | osd_cat --shadow=2 --align=center 
 ↪--pos=bottom --color=green --delay=2 
 ↪--font=lucidasanstypewriter-bold-24 --offset 40 &
# choose my laptop screen's resolution by default, 
# if that fails try the auto-detected mode
    xrandr --output VGA --mode 1280x768@60 || xrandr 
 ↪--output VGA --auto
else
    echo "LVDS only" | osd_cat --shadow=2 --align=center 
 ↪--pos=bottom --color=green --delay=2 
 ↪--font=lucidasanstypewriter-bold-24 --offset 40 &
    xrandr --output VGA --off &
fi

I also created a separate version of the script that spans across both screens instead of mirroring. I chose to span below my current screen (with the --below LVDS option), but most people probably will prefer to use --right-of or --left-of:

#!/bin/sh

if xrandr | grep -q 'VGA connected'; then
    echo "LVDS + VGA span" | osd_cat --shadow=2 --align=center 
 ↪--pos=bottom --color=green --delay=2 
 ↪--font=lucidasanstypewriter-bold-24 --offset 40 &
    xrandr --output VGA --mode 1280x768@60 --below LVDS || xrandr 
 ↪--output
VGA --below LVDS --auto
else
    echo "LVDS only" | osd_cat --shadow=2 --align=center 
 ↪--pos=bottom --color=green --delay=2 
 ↪--font=lucidasanstypewriter-bold-24 --offset 40 &
    xrandr --output VGA --off &
fi