A while back, I posted an example of a calculator with a simple one-dimensional editor. Now, I am working on a two-dimensional editor and am wondering how one might implement redo/undo.

Specifically, if the user types "hello", we do not want this to become 5 undoable actions, but would rather have these fused into a single undoable action.

You can look at the fedit sources as an example of one possible approach. Usually any editing operation makes a new undo point (with "store_status_for_undo" function), but if there are several letters typed in succession, they do not make new points, they just add to the existing one (with "store_segment_for_undo").

There are also some other specific commands, like backspace, that are grouped this way. Using any other command, even one that does not edit text (like arrow keys) breaks the sequence and causes the next character (or backspace etc.) to make a new undo point.

It sounds like the undo buffer would then contain whole lines? For 1D sources the text is usually broken into many short (~80 char) lines. However, for 2D sources this is not the case and storing whole "lines" would become too expensive.

No, fedit breaks lines into segments, too. Though insertion/deletion is not handled very well.

So then what do you think is a good way to handle it?
In a 1D source we might have

and it is just a 1D array of chars. For example the position of the "d" is simply 7. The basic operations could be something like
1. insert m characters at position n
2. delete m characters from position n
3. move m characters from position n1 to position n2


In a 2D source, we now have

stored in a tree something like

The address of the "d" is now 0,2,1,2,0,0

Maybe if nothing was written for half a second, place what was written until last undo point into the undo history. Exceptions would be stuff like backspace (or moving the cursor) I guess, which might always have to create an undo point? (unless in succession, same rule as above)

tthsqe, from personal experience i recommend you plug-in fedit and focus on the main dev line except you are planing inclusion of multiline math symbols