9.5.2

158 • CHAPTER 6
EDIT MENU • 159
Undo (Action)
This function differs from the conventional Undo command in that it ignores selection actions. Undo
(Action) undoes the last change that did not involve selection.
Why does the command ignore selection actions? Suppose you’ve scaled an object and used ten
selection actions to select points in various locations. You then decide that the object is too large and
want to restore it to its original size. This would require you to call the conventional Undo command
11 times, to undo the 10 selection actions and then nally the scale action. However, if you use Undo
(Action), it skips over the selection actions and undoes the scale action immediately.
Let’s explore a couple of examples; in these example, A stands for a normal action such as moving an
object and S stands for a selection action such as selecting edges.
Example
You’ve been editing for a while. The undo buffer contains the following
sequence:
A S A S A A A S S S S
i.e. the buffer starts with a normal action, followed by a selection action,
followed by a normal action, and so on. There are four consecutive selection
actions at the end of the buffer. The nal, most-recent, selection action is
right-most and represents the current state of the undo buffer. If we call the
normal undo function, the resulting buffer is:
A S A S A A A S S S
Only the nal selection has been removed — there are still three selection
actions at the end of the buffer. However, if we use the Undo (Action) function
instead of the normal undo we get:
A S A S A A
The rst normal action has been removed as well as all the selections that
happened to be in front of it.
The clipboard
When you use the Cut or Copy commands, the selected objects or elements are copied into a structure
in memory known as the clipboard. When you select the Paste command, the data in the clipboard
is inserted into the current scene. For example, to copy an object from one scene to another scene,
open both scenes, activate the scene that contains the object, copy the object, activate the other
scene and then paste.