Re: Programming challenge: Undo

[Bill Troop billtroop@xxxxxxxx]

> does up to
> 998 levels of UnDo|ReDo, which ought to be enough for anybody.
> And is completely unobtrusive.  Zero CPU consumption, and
> fast.


That really is pretty amazing, given everything - - the age of the
program, the fact that it was never set up to do this, etc. etc.


Robert, isn't there a sort of basic keyboard recorder undo mechanism in
XyWrite?


If you type the word 'anything' and then backspace over it, without doing
anything else, 'undelete', instead of presenting you with its
customary menu, will simply play back the deleted letters, exactly in
place.


All of this makes me interested in the history of the undo command. Where
did it come from? Who thought of it first? Where was it first
implemented? How did it permutate? It has a kind of Mac-feel to it -- -
did it come from Xerox Parc?


The Wikipedia entry on undo has some slightly interesting links, one of
which touches on the interesting question of saved undos, claiming, madly
it seems to me, that saved undos should not take up significant
space.


Robert, one last throught.


In the program Fontographer (the ultimate predecessor of Freehand and
Illustrator), there are three layers in which you can work: foreground,
background, and guideline layer. Each layer has entirely separate
undo. The more modern successor program Fontlab does not have this
facility - - undo is a literal simplistic model which even includes as an
undoable event the act of cursor selection. Very bad thinking. I'm
wondering if the Fontographer model might not help somewhere as you are
working through the XyWrite issues.


I want to bring up another serious issue. I am typing this in Eudora. I
just had to use undo because some accidental keyboard/trackpad stroke
caused a sentence to be deleted. It was a complex chain of events - -
something like 'select sentence, replace with the letter K, then move
cursor up' -- all over with in a millisecond.


That's where all of us who use Windows programs really love Windows style
immediate character undo.


The significant thing to keep in mind with XyWrite, though, is that
you don't make this kind of mistake in XyWrite, so you don't find
yourself often needing this kind of undo.

In other words, Windows (and Mac!) undo is partly so necessary
because of the too frequent misbehaviour of the entire software/hardware
model. XyWrite breaks that by not being so intimately hooked up with the
hardware.


What I'm getting at is just a feeling that what I thought needed priority
probably shouldn't have priority. - - sorry for rambling on so!