Useful Things You Can Do with FVWM

I have a script called convert-xwd that makes the process of converting a slew of XWD files much easier. If you supply arguments, it assumes they're the names of XWD files and converts them to PNG format. If you supply no arguments, it finds all of the XWD files in the current directory and converts them. After successfully converting an XWD file to PNG, it deletes the XWD file. Here's the script:

  #!/bin/bash

  main() {
    if [ $# = 0 ]
    then
      do_files *
    else
      do_files "$@"
    fi
  }

  do_files() {
    local file

    for file in "$@"
    do
      if file "$file" | fgrep -q ": XWD X-Windows Dump image data,"
      then
	echo "Doing $file"
	convert "$file" "$file.png" && rm "$file"
      fi
    done
  }

  main "$@"

I've given two sample invocations of savescreenshot. Now it's time to explain what they do. As the accompanying labels suggest, when run with no arguments, savescreenshot simply saves a screenshot, and when passed the -n option, it saves and names a screenshot.

savescreenshot uses two directories, $HOME/.screenshots/t and $HOME/.screenshots/n. If they don't exist, it creates them. In the first directory, savescreenshot saves a screenshot whose name has the form of NNN-HHMM.SS. NNN is a three-digit number representing the number of the day in the year, HH is a two-digit number representing the hour, MM is a two-digit number for the minute and SS is a two-digit number for the second.

The second directory, $HOME/.screenshots/n, is left untouched unless the -n option was given. If it was, savescreenshot pops up a window to ask the user what name the screenshot should have. After the user has answered, savescreenshot creates a symbolic link, using the name entered in the popup window, in $HOME/.screenshots/n pointing to the screenshot in $HOME/.screenshots/t.

The user needs to know when the screenshot has been taken so that he can continue interacting with the window he's dumped. xwd beeps when it's finished, but in case you have the bell disabled, as I do, savescreenshot also makes the screen flash red when xwd has completed.

Here's the savescreenshot program. I don't believe it needs much comment. One thing to note, however, is it handles prompting the user for a name by invoking itself again with a private option.

Another interesting feature is the savescreenshot program attempts to delay the screenshot a little if it believes the window may be slow to update. This can happen with windows whose contents are fetched over a network. Examples of applications that create such windows are remote administration programs such as VNC and rdesktop.

  #!/bin/bash

  main() {
    dir=~/.screenshots
    timedir=$dir/t
    namedir=$dir/n

    test -e "$timedir" || mkdir -p "$timedir"
    test -e "$namedir" || mkdir -p "$namedir"

    menu_linger_time=.1

    # we wait this amount of time to allow for the menu obscuring the
    # window to disappear.

    prompt_for_name=false

    timestamp=`date +%j-%H%M.%S`

    case "$1" in
      -n)
	prompt_for_name=true
	shift
      ;;
      -p)
	timestamp=$2
	read -p "Please supply name for screenshot: " name
	ln -s "../t/$timestamp" "$namedir/$name" 
	exit
    esac

    window_id=$1

    sleep $menu_linger_time

    sleep `get_delay_for_update $window_id`

    xwd -id "$window_id" -out "$timedir/$timestamp"

    xrefresh -solid red
    # this is to inform the user that xwd has finished.

    sleep .5
    xrefresh -solid red

    # just in case the user blinked and missed the first flash.

    if $prompt_for_name
    then
      title="Please supply name..."
      x rxvt -T "$title" -n "$title" -e "$0" -p "$timestamp"
    fi
  }

  # this function estimates how long it will take the application to repaint
  # the part of the window uncovered when the FVWM menu obscuring it disappears.
  # most applications repaint almost instantaneously, but some applications which
  # need to fetch data over a network in order to repaint take a little time.
  # 
  # this method isn't failsafe, because the window's title may have been 
  # manually changed.

  get_delay_for_update() {
    local window_id=$1

    case "`window_title "$window_id"`" in
      TightVNC:\ *)
	echo 2
      ;;
      rdesktop\ *)
	echo 1
      ;;
      *)
	echo 0
    esac
  }

  window_title() {
    local window_id=$1

    xwininfo -id "$window_id" | perl -ne 'if(/"(.*)"\s*$/) { print $1; exit }'
  }

  main "$@"

Making screenshots is a good thing to know how to do, but sometimes you want to capture continuous video. Here's a link to an interesting article on Newsforge that describes how to do this task.

Your FVWM undoubtedly is configured to put a titlebar at the top of every window. To be entirely accurate here, I should have said nearly every window. Some applications, such as xbiff, create small persistent windows, and putting a titlebar on them would clutter the screen needlessly. These titles also are used by window-listing facilities, such as FVWM's WindowList command or its FvwmWinList module.

Below I present a program that easily changes the title on a window. It is invoked by opening the window operations menu--the same one we modified in the previous section--choosing the Change title option and entering the new title when prompted, whereupon the window's title is changed.

I often find that I have many windows open at one time. They obscure one another, of course, so the only way to manage them and bring up the one I want when I need it is to use some window-listing facility.

In order for me to be able to find the window I want in the list, windows need to have informative titles. Applications don't always choose informative titles for their windows, however. Furthermore, sometimes the functions of windows change over time, making the initial title inappropriate. Other times, I start several instances of one application, and they all use the same title, making it impossible to distinguish between them.

I've covered modifying FVWM menu definitions in an earlier section (see FVWM Menu Definitions), so I won't go over it again. Instead, below is the line you need to add to the relevant menu definition in order to be able to change the title:

+   "Change &title" Exec set-new-title $w

As before, if set-new-title isn't in the PATH, you have to use an absolute pathname.

Here's the program, called set-new-title. It relies on xwit, which is the utility that actually changes the title.

  #!/bin/bash

  set -u

  main() {
    window_id=$1

    title=`xwininfo -id "$window_id" | perl -ne 'print $1 if /"(.*)"\s*$/'`

    if ! tempfile=`mktemp` 
    then
      echo "Cannot create temporary file" 1>&2
      exit 1
    fi

    echo "$title" > "$tempfile"

    popup_window_title="Choose new title in editor, then save and exit..."

    rxvt -T "$popup_window_title" -n "$popup_window_title" \
      -e "${EDITOR:-vi}" "$tempfile"

    newtitle=`head -c 1000 "$tempfile"`

    xwit -id "$window_id" -name "$newtitle"
  }

  main "$@"