proc clear_display {} {
global iddrawn linesegs need_redisplay nrows_drawn
global vhighlights fhighlights nhighlights rhighlights
+ global linehtag linentag linedtag
allcanvs delete all
catch {unset iddrawn}
catch {unset linesegs}
+ catch {unset linehtag}
+ catch {unset linentag}
+ catch {unset linedtag}
catch {unset vhighlights}
catch {unset fhighlights}
catch {unset nhighlights}