dotcanvas - canvas widget and application tied to a GraphViz dotfile with automatic updates if the file changes.


DDG 2021-09-04: dotcanvas is a special canvas widget and application with automatic rendering of a GraphViz dotfiles. If the users edits the file, the canvas widget automatically updates the display. This is nice to have a live preview of the dot file beside of your editor. The user can as well save the current display as png, svg, pdf image.



Below is a simple dot-file:

digraph G {
    A -> B;
    A -> C;
    C -> D;

You can render this dot file by using the command line:

tclsh dotcanvas.tcl

If you edit the dot-file in your text editor, the canvas will be automatically update, errors will be shown in the label at the bottom.


Below is an image of the running application.


Source code

Below the initial source code from the first version. The latest version should be take from the GitHub page . The code is inspired by the Wiki page File watch. Thanks for the code!

package require Tk
package provide dotcanvas 0.1

namespace eval dotcanvas {
    variable fname ""
    proc wcanvas {w file {mtime -}} {
        set checkinterval 1000 ;# modify as needed
        if {$mtime eq "-"} {
            if [info exists ::_cwf] {after cancel $::_cwf}
            set file [file join [pwd] $file]
            [namespace current]::wcanvas $w $file [file mtime $file]
        } else {
            set newtime [file mtime $file]
            if {$newtime != $mtime} {
                [namespace current]::canvasupdate $w $file
                [namespace current]::wcanvas $w $file
            } else {set ::_cwf [after $checkinterval [info level 0]]}
    proc canvasupdate {w file} {
        variable fname 
        if {$fname eq ""} {
            $w delete all
        set dot ""
        if {$::tcl_platform(os) eq "Linux"} {
            set dot dot
        } else {
            if {[file exists "C:/Program Files/GraphViz/bin/dot.exe"]} {
                set dot "C:/Program Files/GraphViz/bin/dot.exe"
            } elseif {[file exists "C:/Programme/Graphviz/bin/dot.exe"]} {
                set dot "C:/Programme/Graphviz/bin/dot.exe"
            if {$dot eq ""} {
                tk_messageBox -title "Error!" -icon error -message "GraphViz application not found!\nInstall GraphViz!" -type ok
        if {[catch {
             set res [exec $dot -Ttk $file]
             #puts $res
             set c $w
             $c delete all
             eval $res
             set ::einfo "File [file tail $file] is ok! [clock format [file mtime $file]]"
         }]} {
                $w configure -background salmon
                after 1000
                set ::einfo [regsub {.+dot:(.+)\n +while.+} $::errorInfo "\\1"]
                $w configure -background white
    proc dotcanvas {path {dotfile ""}} {
        variable fname
        set fname $dotfile
        canvas $path -background white -width 200 -height 200 -borderwidth 10 -relief flat
        if {$dotfile ne ""} {
            [namespace current]::wcanvas $path $dotfile
            [namespace current]::canvasupdate $path $dotfile
        return $path
if {[info exists argv0] && $argv0 eq [info script]} {
    if {[llength $argv] > 0} {
        if {[lindex $argv 0] eq "--help"} {
            puts "dotcanvas.tcl"
        } elseif  {[lindex $argv 0] eq "--version"} {
            puts "[package present dotcanvas]"
        } elseif {[file exists [lindex $argv 0]]} {
            set ::einfo ""
            pack [dotcanvas::dotcanvas .c [lindex $argv 0]] -fill both -expand true  -padx 5 -pady 5 -ipadx 5 -ipady 5
            pack [ttk::label .l -textvariable  ::einfo] -side top -fill x -expand false -padx 5 -pady 5
        } else {
            puts "Error: File [lindex $argv 0] does not exists!"
            exit 0
    } else {
       puts "dotcanvas.tcl"   


  • make einfo namespace var (done, see github)
  • tied text and canvas widget together
  • other layout engines, neato, fdp etc
  • standalone widget with documentation, more than one display is possible
  • widget disable auto-update if requested
  • OSX port (help required here, plz, have no MacOSX)

See also


DDG - 2021-09-04: I just updated the GitHub code to version 0.2.0 which offers as well the possibility to save the current dotfile as svg, jpg, png, pdf etc. I know that can be easily done from the terminal, but for my Win-users that was required. I knwo that as well you can do as similar live edit using the: dot -Tx11 syntax. I found the canvas approach more feasible as it allows me to embed the live preview facility into a Tcl-application.