Re^3: getting visible area of Tk::Scrolled?

Use $canvas->get_corners to obtain the bounding box of the visible portion of the canvas.

See also the return lists from the ->xview() & ->yview() methods which are useful for manipulating the scrollbars.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re^3: getting visible area of Tk::Scrolled? Select or Download Code

Replies are listed 'Best First'.
Re^4: getting visible area of Tk::Scrolled? by halley (Prior) on Sep 19, 2011 at 20:42 UTC
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'); }` [download] Without starting any timers or anything, it's a little chunky, but it's pretty useful and dead simple. -- `[ e d @ h a l l e y . c c ]`	[reply] [d/l]

Replies are listed 'Best First'.

Re^4: getting visible area of Tk::Scrolled?
by halley (Prior) on Sep 19, 2011 at 20:42 UTC

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'); }
[download]

Without starting any timers or anything, it's a little chunky, but it's pretty useful and dead simple.

--
[ e d @ h a l l e y . c c ]

[reply]
[d/l]