From: Hidetoshi NAGAI <nagai@...>
Date: 2011-03-02T07:31:52+09:00
Subject: Re: tk canvas drag items

From: Ignatz Hafflegab <mcpeople@hotmail.com>
Subject: Re: tk canvas drag items
Date: Tue, 1 Mar 2011 12:06:19 +0900
Message-ID: <70c564908d72fa5bff5bb1fd5b562698@ruby-forum.com>
> What I'm looking for is an example that will confine a selected item
> within the boundaries fixed-size canvas while the item is dragged.

It's not difficult.
Please select "A simple 2-D plot" on widget-demo, 
and press "Show Code" button on the plot-demo window.
On the "Demo Code" window, please edit plotMove method like the following.
-----------------------------------------------------
def plotMove (w, x, y)
  if x < 0
    x = 0
  else
    width = w.winfo_width
    x = width if x > width
  end
  if y < 0
    y = 0
  else
    height = w.winfo_height
    y = height if y > height
  end
  w.move 'selected', x - $plot['lastX'], y - $plot['lastY']
  $plot['lastX'] = x
  $plot['lastY'] = y
end
-----------------------------------------------------
As you see, it checks whether the coordinates are within the canvas window.
If you want control the region by canvas coordinates, you mark (on PlotDown
method) and check coords by canvas coords.

After editing, click "Rerun Demo" button on the editor window.
And then, dragging the points on the restarted demo will be restricted
by the canvas window size.
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)
Department of Artificial Intelligence, Kyushu Institute of Technology