Undo
Surpac uses an efficient storage structure to minimise the amount of memory used for storing previous versions of the graphics layer. Only a small amount of extra memory will be used when the operation makes minor changes to a layer, for example, retaining undo information about deleting a point does not use much memory since the before and after versions are almost identical. However, substantial memory may be used if the layer is changed completely, for example, undo information for recalling a file requires memory to store the previous version as well as the current version since no part of the layer is shared between the before and after versions.
To prevent excessive memory being used for previous versions the number of undo versions, i.e. the number of operations for which undo information can be kept at a time is limited and is set by the user default "maximum undo operations" (in the defaults.ssi file) or can be modified by Undo Setup. To further reduce memory when using Recall File, all undo information except for the immediately preceding version, is destroyed. The user default ``clear undo on recall file'' may be set to ``off'' to ensure that edit operations before the recall file operation can be undone.
Undo functionality can be turned on or off using Undo Off or Undo On. The undo parameters can be modified via Undo Setup and the current undo history can be purged using Undo Clear.
Note: When operations are undone or redone sometimes triobjects, trisolations,
strings, segments, or points will not be redrawn in exactly the same manner
as in the original version. This is particularly noticeable when a deleted
entity is redrawn when the delete is undone.
To run this function: Choose Edit > Undo, or...
Undo the current operation for the current work layer.
Note: Undo and Redo operations work on both string and triangle data.
The last operation performed on the layer will be undone.
Undone Operation <operation name>
Indicates that Undo was able to successfully undone the indicated operation.
No undo information for current layer
Indicates that Undo functionality is not enabled, or that there is no more undo information on the Undo stack.
Redo
Redo a previously undone operation (via Undo) provided no changes have been made to the current graphics layer since the last Undo or Redo.
Any previous operation which has be undone will be redone.
To run this function: Choose Edit > Redo, or...
Redone Operation <operation name>
Indicates that Redo was able to successfully redo the indicated operation.
No undo information for current layer
Indicates that no operations have been undone which can be redone.