Block undo and redo while a background job runs

A job is queued against the model as it stands and hands its result back
when it finishes, so undoing underneath it leaves that result landing on
geometry it was never computed for. Undo and redo now wait for the job
and say so, and can_undo()/can_redo() report the same, so the toolbar
and the menu items stay in step.

src/slic3r/GUI/Plater.cpp

@@ -7297,6 +7297,8 @@ struct Plater::priv
 
     void undo();
     void redo();
+    // True, and tells the user, while a background job is working on the model - see the definition.
+    bool undo_redo_blocked_by_job();
     void undo_redo_to(size_t time_to_load);
 
     // BBS: backup
@@ -14933,8 +14935,25 @@ void Plater::priv::take_snapshot(const std::string& snapshot_name, const UndoRed
     BOOST_LOG_TRIVIAL(info) << "Undo / Redo snapshot taken: " << snapshot_name << ", Undo / Redo stack memory: " << Slic3r::format_memsize_MB(this->undo_redo_stack().memsize()) << log_memory_info();
 }
 
+// A background job holds the model it is working on: it was queued against the geometry as it stood at
+// the time and hands its result back when it finishes. Undoing while it runs restores an older state
+// underneath it, a different transform or a different mesh, and the result then lands on geometry it
+// was never computed for. Undo and redo therefore wait for the job, and say so rather than doing
+// nothing.
+bool Plater::priv::undo_redo_blocked_by_job()
+{
+    if (m_worker.is_idle())
+        return false;
+    notification_manager->push_notification(NotificationType::CustomNotification,
+                                            NotificationManager::NotificationLevel::RegularNotificationLevel,
+                                            _u8L("Cannot undo or redo while an operation is running. Stop it first."));
+    return true;
+}
+
 void Plater::priv::undo()
 {
+    if (this->undo_redo_blocked_by_job())
+        return;
     const std::vector<UndoRedo::Snapshot> &snapshots = this->undo_redo_stack().snapshots();
     auto it_current = std::lower_bound(snapshots.begin(), snapshots.end(), UndoRedo::Snapshot(this->undo_redo_stack().active_snapshot_time()));
     // BBS: undo-redo until modify record
@@ -14952,6 +14971,8 @@ void Plater::priv::undo()
 
 void Plater::priv::redo()
 {
+    if (this->undo_redo_blocked_by_job())
+        return;
     const std::vector<UndoRedo::Snapshot> &snapshots = this->undo_redo_stack().snapshots();
     auto it_current = std::lower_bound(snapshots.begin(), snapshots.end(), UndoRedo::Snapshot(this->undo_redo_stack().active_snapshot_time()));
     // BBS: undo-redo until modify record
@@ -22808,8 +22829,9 @@ bool Plater::can_copy_to_clipboard() const
     return true;
 }
 
-bool Plater::can_undo() const { return IsShown() && p->is_view3D_shown() && p->undo_redo_stack().has_undo_snapshot(); }
+// The job check keeps the buttons in step with priv::undo()/redo(), which refuse while one runs.
-bool Plater::can_redo() const { return IsShown() && p->is_view3D_shown() && p->undo_redo_stack().has_redo_snapshot(); }
+bool Plater::can_undo() const { return IsShown() && p->is_view3D_shown() && p->m_worker.is_idle() && p->undo_redo_stack().has_undo_snapshot(); }
+bool Plater::can_redo() const { return IsShown() && p->is_view3D_shown() && p->m_worker.is_idle() && p->undo_redo_stack().has_redo_snapshot(); }
 bool Plater::can_reload_from_disk() const { return p->can_reload_from_disk(); }
 //BBS
 bool Plater::can_fillcolor() const { return p->can_fillcolor(); }