Each operation on the project graph is performed through a transaction. These transactions are logged in a cache. It is possible to read through this log and apply the transaction in reverse enabling undo-ing the last modifications.
The commands are:
Logged transactions can be reversed, allowing the system to perform an “undo” operation on previous changes.
The log also keeps track of transactions that have been undone, enabling you to “redo” them if needed. Undo and redo operations can be performed in sequence (a “chain”), but once a new command is executed, the chain of possible redos is cleared. Thus, it is possible to re apply the transactions previously “undone”. Yet, one a new transaction is performed (running a new RGG function, applying a modification through the attribute editor, adding an object through the menu, …) the chain of transaction do not lead to the “redo” anymore. Thus, it is not possible to “undo” > apply new > “redo”.
Note: applying a transaction take some time. Clicking very fast between undo/redo, might trigger a transaction before the last one is properly performed. It usually lead to a NullPointerException.