can't read "x1": no such variable
"expr {($x1+$x2)/2}" (procedure "rect_centre" line 3)
"rect_centre [[$_($self:canvas) widget] bbox ${from}i${port}]" (procedure "FutureWire_init" line 21)
"FutureWire_init o0000029 x80b2dd0 591.0 29.0 256 {outlet x80c03d8 0}" ("eval" body line 1)
"eval [concat [list [lindex $methods 0] o0000029] $args]" (procedure "o0000029" line 4)
"o0000029 init x80b2dd0 591.0 29.0 256 {outlet x80c03d8 0}" ("eval" body line 1)
"eval [list $self init] $args" (procedure "FutureWire_new" line 6)
"FutureWire_new x80b2dd0 591.0 29.0 256 {outlet x80c03d8 0}" ("eval" body line 1)
"eval [concat [list ${self}_new       ] $args]" (procedure "Class_new" line 1)
"Class_new FutureWire x80b2dd0 591.0 29.0 256 {outlet x80c03d8 0}" ("eval" body line 1)
"eval [concat [list [lindex $methods 0] FutureWire] $args]" (procedure "FutureWire" line 4)
"FutureWire new $self $x $y $f $target" ("outlet" arm line 3)
"switch $type {
		outlet {
			if {$_($self:action) == "none"} {
				set _($self:action) [FutureWire new $self $x $y $f $target]
			}
			return
		}
		in..." (procedure "Canvas_click" line 14)
"Canvas_click x80b2dd0 591.0 29.0 256 {outlet x80c03d8 0}" ("eval" body line 1)
"eval [concat [list [lindex $methods 0] x80b2dd0] $args]" (procedure "x80b2dd0" line 4)
"$self click $x $y $f $target" (procedure "Canvas_click_wrap" line 7)
"Canvas_click_wrap x80b2dd0 593 40 1 0" ("eval" body line 1)
"eval [concat [list [lindex $methods 0] x80b2dd0] $args]" (procedure "x80b2dd0" line 4)
"x80b2dd0 click_wrap 593 40 1 0 " (command bound to event)