Tcl - Range of characters changed by edit undo

Author

Range of characters changed by edit undo

Francois Vogel

2005-06-04, 8:57 pm

Hi all,

I'm making use of the edit undo capability of the text widget.

Iwould like to know which range(s) of characters were modified by an undo.
In other words, I would like to know at which index in the text the internal
undo stuff started to insert or delete characters, and at which index it
stopped.

I tried to use a tag the following way (simplified, should work only to undo
a delete near the middle of the text):
$w tag add unchanged 1.0 end
event generate $w <<Undo>>
set range1 [$w tag nextrange unchanged 1.0]
set i1 [lindex $range1 1]
set range2 [$w tag nextrange unchanged $i1]
set i2 [lindex $range2 0]
$w tag remove unchanged 1.0 end
# here I do my stuff with the characters that were changed, e.g. colorize
them, and I thought they would be located between $i1 and $i2

But this does not work since apparently the characters inserted by undo also
has the "unchanged" tag (surprising!), which ends up with $range1 being the
full text and $range2 being empty.

What else could I do?

It would be nice if [.t edit undo] would return this range, but maybe there
is another way.

Thanks for any hint,
Francois

Francois Vogel

2005-06-05, 8:56 am

Hmm, I found the following implementation, that seems to work:

set bef [$w get 1.0 end]
event generate $w <<Undo>>
set aft [$w get 1.0 end]
set pref [commonPrefix $bef $aft]
set i1 [$w index "1.0 + [string length $pref] chars"]
set rbef [srevert $bef]
set raft [srevert $aft]
set pref [commonPrefix $rbef $raft]
set i2 [$w index "end - [string length $pref] chars"]
# here colorization between $i1 and $i2

Procs srevert and commonPrefix can be found at http://wiki.tcl.tk/44
(additional string functions).

I was a bit afraid wrt performance, but it seems to be quite reasonable even
for large (15000 lines) text widget content.

If anybody has a better idea, please share.

Francois

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