I am playing around some more with Tk::Canvas, and in particular, the scrolled variety. The scrollbar mechanisms seem really primitive.

    my $c = $parent->Scrolled('Canvas',
                  -width  => $width,
                  -height => $height,
                  -background => 'beige',
                  -scrollbars => 'osoe',
                  -scrollregion => [ 0, 0, $width, $height ]);
[download]

I've constructed a Scrolled Canvas, which apparently returns a ref of type Tk::Frame. That must have the children, including a Canvas and a couple of Scrollbars.

I also found the Tk::Autoscroll class, which didn't come with my build of Perl/Tk, but was easy enough to add.

When dragging around an item in a large scrolled canvas, I want to auto-scroll to keep the dragged item in view. This doesn't seem so hard, except knowing where the scroller is viewing at the current time.

I can't figure out the way to go from a blessed Canvas ref (given in the drag events), to calculate or query the area of the scrollregion that is currently visible.

Before I go digging farther, I bet someone already has some code that calculates the visible area.