Thanks for all your comments.

I have requested the namespace Tk::Canvas::Draw, which I agree seems like the best choice.

zentara:  Certainly bezier lines would be a good addition; I'll plan to include them soon.  As far as saving data for later, you could do that very easily with use Storable, so I didn't explicitly provide the capability.  And when you say:

    "...an eraser function for the lines"

You do realize, don't you, that the IDs of all lines/shapes drawn are passed to the results subroutine?  Thus, deleting those shapes is as easy as:

my $o_obj = new Tk::Draw($c1, \&done_drawing, $h_opts);

sub done_drawing {
    my ($o_obj, $a_points, $a_ids) = @_;
    map { $o_obj->canvas->delete($_) } @a_ids;
}
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But perhaps I'll simplify that further, and provide a delete_shapes method to the object.

hangon:  Thanks for confirming the name (Tk::Canvas::Draw) that I was considering as an alternative for the module.

As for your two specific suggestions, plugins and "snapping points to a shape", if you wouldn't mind providing me with more details, or even some example code, I'd be more than happy to consider both of them.