Undo

Undo

Undo is a command in many computer programs. It erases the last change done to the document reverting it to an older state. In some more advanced programs such as graphic processing, undo will negate the last command done to the file being edited.

The opposite of undo is redo. The redo command reverses the undo or advances the buffer to a more current state.

In most Windows applications, the Undo command is activated by pressing Ctrl-Z or Alt-Backspace. In most Macintosh applications, the Undo command is activated by pressing Command-Z. The common command for Redo on Microsoft Windows systems is Ctrl-Y or Ctrl-Shift-Z. The common command for Redo on Apple Macintosh systems is Command-Shift-Z.

Undo models

Undo models can be categorized according to two criteria: linear vs non-linear, and single-user vs multi-user. Linear undo requires the user to revert the latest action before undoing earlier ones. With non-linear undo, the action to be reverted can be freely picked from the action history list.

Non-linear undo can be further subcategorized into direct selective undo vs. script interpretation undo vs. cascading undo.

When multiple users can edit the same document simultaneously, a multi-user undo is needed. "Global" multi-user undo reverts the latest action made to the document, regardless of who performed the edit. "Local" multi-user undo only reverts actions done by the local user. Local multi-user undo usually requires a non-linear undo implementation.

The number of previous actions that can be undone varies by program. For example, the stack size ranges from twenty in Photoshop to three edits in MS Paint. Simplistic, single-edit undo features sometimes do away with "redo" by treating the undo command itself as an action that can be undone. This is known as the flip undo model, because the user can flip between two program states using the undo command.

Undo implementation

The Command pattern is a software design pattern which can be used to implement Multi-level Undo. The Memento pattern is useful for capturing the state of the program before user actions. This can be used for state reversal needed in some undo implementations.

External links

* [http://www.chronicallyunemployed.com/main_stuff/tech/undo.htm Gradual Undo] - an attempt to improve upon traditional undo functionality.
* [http://e-texteditor.com/blog/2006/making-undo-usable A Modern Undo - Making undo usable beyond the last few changes] - remarkable enhancements to traditional undo, including safe "what if" branching.
* [https://dip.felk.cvut.cz/browse/pdfcache/vratij1_2008bach.pdf Cascading undo control] - a paper focused on what is cascading undo and how it might be presented to users

* [http://www.youtube.com/watch?v=E7naCU8X2cU Cascading undo prototype: Fisheye-detail] - prototype of proposed visualizations

* [http://www.youtube.com/watch?v=nMiSbVOrKmQ Cascading undo prototype: Fisheye-scrollbar] - prototype of proposed visualizations


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  • Undo — (englisch für zurücknehmen, rückgängig machen) bzw. Rückgängig (machen), Zurücknehmen oder Zurücknahme bezeichnet die Funktion von Anwendungsprogrammen, mit der eine oder mehrere Aktionen zurückgenommen werden können. Je nach Umfang der Anwendung …   Deutsch Wikipedia

  • Undo — Un*do , v. t. [AS. und?n. See 1st {Un }, and Do to perform.] 1. To reverse, as what has been done; to annul; to bring to naught. [1913 Webster] What s done can not be undone. Shak. [1913 Webster] To morrow, ere the setting sun, She d all undo… …   The Collaborative International Dictionary of English

  • Undo It — Single par Carrie Underwood extrait de l’album Play On Sortie 24 mai 2010 Durée 2:57 (version album) Genre Country pop Format …   Wikipédia en Français

  • undo — [v1] open disengage, disentangle, free, loose, loosen, release, unbind, unblock, unbutton, unclose, unfasten, unfix, unlock, unloose, unloosen, unravel, unshut, unstop, untie, unwrap; concept 135 Ant. close, do, fasten undo [v2] nullify,… …   New thesaurus

  • undo — index abolish, abrogate (annul), beat (defeat), betray (lead astray), counteract, denude …   Law dictionary

  • undo — O.E. undon to unfasten and open (a window or door), to unfasten by releasing from a fixed position, from UN (Cf. un ) (2) + DO (Cf. do). The notion is of to annul something that was done. Related: UNDONE (Cf. Undone); UNDOING (Cf. undoing) …   Etymology dictionary

  • undo — (izg. àndu) m DEFINICIJA inform. naredba u računalnim programima za vraćanje prethodnog stanja (npr. prije napisanoga teksta ili pokrenute neke opcije) ETIMOLOGIJA engl …   Hrvatski jezični portal

  • undo — ► VERB (undoes; past undid; past part. undone) 1) unfasten or loosen. 2) cancel or reverse the effects of (a previous action or measure). 3) formal cause the downfall or ruin of …   English terms dictionary

  • undo — [un do͞o′] vt. undid, undone, undoing [ME undon < OE < un ,UN + don, to DO1] 1. a) to release or untie (a fastening) b) to open (a parcel, door, etc.) by this means …   English World dictionary

  • undo — [[t]ʌ̱ndu͟ː[/t]] undoes, undoing, undid, undone 1) VERB If you undo something that is closed, tied, or held together, or if you undo the thing holding it, you loosen or remove the thing holding it. [V n] I managed secretly to undo a corner of the …   English dictionary

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