Edit - Undo / Redo

A limited form of Undo and Redo that provides single-step undo and redo capabilities in certain contexts when ambiguities can be resolved. Comments, queries and scripts allow multi-level Undo and Redo. Certain operations (for example, certain remote database operations) cannot be undone.


It is always wise, therefore, to make frequent saves and to always work with copies of important data in case changes get out of hand.


When working with large images and surfaces the Undo command requires the creation of large temporary files. The process of creating such temporary files can be quite slow and result in annoyingly slow performance when working with very large images and surfaces. Many users prefer to turn off Undo in such cases.


The parameters specified in Tools - Options - Confirmation allow users to the size of images and surfaces that preserve the ability to Undo. The Confirm creating undo actions larger than… option provides two controls:


·      The ability to ask for confirmation before an Undo action is undertaken when image or surface size exceeds a given number of megabytes, by default, 50 megabytes.

·      A standing specification to never undertake an Undo action larger than a given number of megabytes, by default, 250 megabytes. If this second parameter is reduced to a very small number of megabytes the effect will be to turn off Undo except for very small images and surfaces.


Note: Script windows, query windows and comments are unusual in that they support multi-level Undo / Redo. One can CTRL-Z (Undo) backwards through many changes and CTRL-Y (Redo) forwards to redo many Undo operations.


Tech Tip


Many transform operators for drawings automatically run a Normalize Topology transform before running to eliminate common errors that may affect correct operation. When such an operator is undone, the normalization that automatically preceded it will also be undone.