From Buzztard

The editor app. needs undo/redo. As a side effect handling undo/redo makes it easy to detect when the song has been changed. If there is nothing to undo since last save (load), it has not been changed ;).

Existing implementations

GUndo

GUndo manages a sequence of actions. Echo action has callbacks for undo/redo and free. One can link toolbar/menu items to the sequence and the allow to go back and forth.

Everytime we add an action, we would need to pack the data + some context into a struct. When an action is added, it refs all related objects.

The GUndoSequence is a default implementation of the GUndoHistory Iface. We could have our own (GUndoSequence subclass?) that also write the history to a log file. This can be used for crash recovery. We can use the BtPersistence Iface to serialize the data objects. Maybe we just need two more callback for a new action (serialize/deserialize). It could store/restore the context and use BtPersistence for the objects.

Examples

add a machine

bt_setup_add_machine(setup, machine)

• object: machine
• parent: setup
• undo: bt_setup_remove_machine(setup, machine)
• redo: bt_setup_add_machine(setup, machine)
• free: g_object_unref(machine)

remove a machine

bt_setup_remove_machine(setup, machine)

• object: machine
• parent: setup
• undo: bt_setup_add_machine(setup, machine)
• redo: bt_setup_remove_machine(setup, machine)
• free: g_object_unref(machine)

entering something in a pattern

bt_pattern_set_global_event(pattern, tick, param, value)

• object: value, old_value, tick, param
• parent: pattern
• undo: bt_pattern_set_global_event(patter, tick, param, old_value)
• redo: bt_pattern_set_global_event(patter, tick, param, value)
• free: ...

Links

Undo/Redo Links

• http://www.codeproject.com/cpp/undoredo_cpp.asp
  • if we cut a selection from a pattern, that is not a full object, like the examples in the article
• http://www.javaworld.com/javaworld/jw-06-1998/jw-06-undoredo.html
• http://www-dse.doc.ic.ac.uk/~np2/software/undo.html