Thanks again for your help, BrowserUk. This is the heart of a drag-an-item handler, so that when dragging near the edge of the scrollable canvas, the canvas automatically scrolls more into view. Otherwise the user must drop, scroll, and grab the item again.

    # move all associated items...
    $c->move($group, $dx, $dy);

    # consider moving the visible area in the scrollregion
    my @corners = $c->get_corners();
    my @bb = $c->bbox($group);
    if ($bb[0] < $corners[0]) { $c->xviewScroll(-1, 'units'); }
    if ($bb[1] < $corners[1]) { $c->yviewScroll(-1, 'units'); }
    if ($bb[2] >= $corners[2]) { $c->xviewScroll(+1, 'units'); }
    if ($bb[3] >= $corners[3]) { $c->yviewScroll(+1, 'units'); }
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Without starting any timers or anything, it's a little chunky, but it's pretty useful and dead simple.