XML Graph to canvas
Richard Suchenwirth 2003-03-25 - In this evening fun project, I played with Tcldot which produces code for rendering a directed graph on a canvas. To make it match work requirements, I decided to represent graphs in XML and control the graph buildup from tDOM's expat parser. The example shows a graph that might be the result of character segmentation, with a "m" alternatively split into "r" and "n". The best path through this (simple) graph is marked with the best="1" attribute, and highlighted on the canvas. Here is the very simple code:
package require tdom
package require Tcldot
set sample {
<graph>
<node id="1" label="H" />
<node id="2" label="a" />
<node id="3" label="m" />
<node id="4" label="r" />
<node id="5" label="n" />
<node id="6" label="b" />
<node id="7" label="u" />
<node id="8" label="r" />
<node id="9" label="g" />
<edge from="1" to="2" best="1" />
<edge from="2" to="3" best="1" />
<edge from="3" to="6" best="1" />
<edge from="6" to="7" best="1" />
<edge from="7" to="8" best="1" />
<edge from="8" to="9" best="1" />
<edge from="2" to="4" />
<edge from="4" to="5" />
<edge from="5" to="6" />
</graph>
}
set c [canvas .c]
pack $c -fill both -expand 1
set g [dotnew digraph rankdir LR]
$g setnodeattribute style filled color white shape box
#------------------- parser callback for element start:
proc start {name atts} {
global g ;# graph
array set a [concat {best 0} $atts]
switch -- $name {
node {
set ::n$a(id) [$g addnode $a(id) label ($a(id))\n$a(label)]
}
edge {
set cmd [list [set ::n$a(from)] addedge [set ::n$a(to)]]
if $a(best) {lappend cmd style bold}
eval $cmd
}
}
}
set parser [expat -elementstartcommand start]
$parser parse $sample
$g layout ;# determine suitable x/y coordinates for canvas items
eval [$g render] ;# put them on the canvas named $c