Tkinter canvas drag/drop obstacle

[Matimus]

On Jun 20, 9:11 am, Peter Pearson <ppear... at nowhere.invalid> wrote:
> Tkinter makes it very easy to drag jpeg images around on a
> canvas, but I would like to have a "target" change color when
> the cursor dragging an image passes over it.  I seem to be
> blocked by the fact that the callbacks that might tell the
> target that the mouse has entered it (<Enter>, <Any-Enter>,
> even <Motion>) aren't called if the mouse's button is down.
> What am I missing?  Have I failed to find the right Tkinter
> document?  Is Tkinter the wrong tool for this job?  Thanks.
>
> --
> To email me, substitute nowhere->spamcop, invalid->net.

I have used a combination of <Motion> and <B1-Motion>. You might also
throw in a <Button-1> event to keep track of whether or not the mouse
button was down when it entered the widget or not.

Depending on what you really want to do though, you might take
advantage of the 'active' state:

import Tkinter as tk

can = tk.Canvas()
can.pack(fill=tk.BOTH, expand=True)

can.create_rectangle(
        10,10,100,100,
        fill="black",
        activewidth=5,
        activeoutline="blue"
        )

can.mainloop()

The 'active*' options take effect when the mouse is on top of that
item.

If all you are _really_ interested in is a visual indicator, this
should work for you. Note that there is also a disabled state. I only
discovered this by looking at the options available and guessing.

>>> from pprint import pprint
>>> import Tkinter as tk
>>> can = tk.Canvas()
>>> can.pack(fill=tk.BOTH, expand=True)
>>> r = can.create_rectangle(10,10,100,100)
>>> pprint(can.itemconfig(r))
{'activedash': ('activedash', '', '', '', ''),
 'activefill': ('activefill', '', '', '', ''),
 'activeoutline': ('activeoutline', '', '', '', ''),
 'activeoutlinestipple': ('activeoutlinestipple', '', '', '', ''),
 'activestipple': ('activestipple', '', '', '', ''),
 'activewidth': ('activewidth', '', '', '0.0', '0.0'),
 'dash': ('dash', '', '', '', ''),
 'dashoffset': ('dashoffset', '', '', '0', '0'),
 'disableddash': ('disableddash', '', '', '', ''),
 'disabledfill': ('disabledfill', '', '', '', ''),
 'disabledoutline': ('disabledoutline', '', '', '', ''),
 'disabledoutlinestipple': ('disabledoutlinestipple', '', '', '', ''),
 'disabledstipple': ('disabledstipple', '', '', '', ''),
 'disabledwidth': ('disabledwidth', '', '', '0.0', '0'),
 'fill': ('fill', '', '', '', ''),
 'offset': ('offset', '', '', '0,0', '0,0'),
 'outline': ('outline', '', '', 'black', 'black'),
 'outlineoffset': ('outlineoffset', '', '', '0,0', '0,0'),
 'outlinestipple': ('outlinestipple', '', '', '', ''),
 'state': ('state', '', '', '', ''),
 'stipple': ('stipple', '', '', '', ''),
 'tags': ('tags', '', '', '', ''),
 'width': ('width', '', '', '1.0', '1.0')}

The 'state' option can be set to 'normal', 'hidden' or 'disabled'. So
if you want to make your canvas items look different when they are
disabled, set the disabled* options and set 'state' to 'disabled'.

Matt