Wow, that's written in a complicated way. As written, it uses input that is explicitly broken up into lines but dlineinfo does give meaningful info when I run it on running text with automatic word wrap:

#!/usr/bin/perl --
use strict;
use warnings;
use Tk;
use Data::Dump qw/ dd pp /;
my $mw = tkinit(qw/ -width 30 -height 30 /);
my $t = $mw->Text(-wrap=>'word')->pack(qw/ -expand 1 -fill both /);
$t->insert('end',
q{"There must be some kind of way out of here," Said the joker to the 
+thief. "There's too much confusion, I can't get no relief. Businessme
+n, they drink my wine, Plowmen dig my earth. None of them along the l
+ine Know what any of it is worth." "No reason to get excited," The th
+ief he kindly spoke. "There are many here among us Who feel that life
+ is but a joke. But you and I, we've been through that, And this is n
+ot our fate. So let us not talk falsely now, The hour is getting late
+." All along the watchtower, Princes kept the view, While all the wom
+en came and went -- Barefoot servants too. Outside in the cold distan
+ce, A wildcat did growl. Two riders were approaching, and The wind be
+gan to howl. http://www.reasontorock.com/tracks/watchtower.html});
# q{"There must be some kind of way out of here," Said the joker to th
+e thief.});


$t->tagConfigure('yellow', -background => "yellow");

my $b = $mw->Button(
    -text    => 'dlineinfo',
    -command => [
        sub {
            my( $mw, $t ) = @_;
            # ffd( $mw, $t, qw/ 1.20  1.12  12.30  15.28    22.16 24.2
+0 /);
            ffd( $mw, $t, qw/ 1.20 1.119 1.333 1.650 /); # 1.1000 to g
+et the last character
        },
        $mw,
        $t,
    ],
)->pack( -before => $t );
$b->focus;
#~ use Tk::WidgetDump; $mw->WidgetDump;
MainLoop();
sub ffff {
    my( $mw, $t ) = @_;
    my $geom = $mw->geometry;
    my( $trooty, $theight ) = ( $t->rooty, $t->height );
    my $ttaily = $trooty + $theight;
    "mw(geo{$geom}) trooty($trooty)+theight($theight)= $ttaily";
}
sub ffd {
    my( $mw, $t ) = splice @_,0,2;
    print "\n", ffff( $mw, $t ), "\n";
    for my $index( @_ ){
        $t->tagAdd('yellow', "$index wordstart", "$index wordend", );
        my @aline = qw/ lTx lTy wpx hpx bsT /;
        my @dline = $t->dlineinfo("$index wordstart");
        my $theword = $t->get( "$index wordstart", "$index wordend" );
        if( not @dline ){
            print "($index $theword) SKIP not visible\n";
            next;
        }
        printf "%-10s %-10s %5s %-5s %5s %-5s %5s %-5s %5s %-5s %5s %-
+5s\n",
            $index,
            $theword,
            map { $aline[$_], $dline[$_]     } 0 .. $#aline,
        ;;;;;
        
        my @bbLine = qw/ lTx lTy lTw lTh /;
        my( @bbLineStart )  = $t->bbox("$index linestart" );
        my( @bbLineEnd )    = $t->bbox("$index lineend" );
        # printf "%-10s %-10s %5s %-5s %5s %-5s %5s %-5s %5s %-5s %5s 
+%-5s\n",,
            # $index,
            # 'end',
            # ( map { $bbLine[$_], $bbLineEnd[$_]     } 0 .. $#bbLine,
+),
            # ('') x 2,
        # ;;;;;
        # printf "%-10s %-10s %5s %-5s %5s %-5s %5s %-5s %5s %-5s %5s 
+%-5s\n",
            # $index,
            # 'start',
            # ( map { $bbLine[$_], $bbLineEnd[$_]     } 0 .. $#bbLine,
+),
            # ('') x 2,
        # ;;;;;
        print "\n";
    }
#~     my $width = (200,400,600)[rand 2];
#~     $mw->geometry( $width."x$width");
}
__END__
[download]

lTy increases by 14 pixels in every new (auto-wrapped) line:

1.20       kind         lTx 3       lTy 3       wpx 525     hpx 14    
+  bsT 11


1.119      relief       lTx 3       lTy 17      wpx 553     hpx 14    
+  bsT 11


1.333      feel         lTx 3       lTy 59      wpx 518     hpx 14    
+  bsT 11


1.650      riders       lTx 3       lTy 115     wpx 553     hpx 14    
+  bsT 11
[download]

So thank you, that brings me closer. I can get the number of lines by doing a ($no - 3) / 14 on an lTy value obtained from the last line. Now I need to try and implement it in Text widgets that are stuck into a TableMatrix table. I expect there could be issues (maybe dlineinfo won't return correct values if the row height isn't tall enough to fit the whole widget when the calculation is done, maybe I'll need to basically draw the table twice, once for calculation and once for display and try and hide it the first time around somehow).