+static boolean checkTapesFromSameLevel(struct TapeInfo *t1, struct TapeInfo *t2)
+{
+ return (strEqual(t1->level_identifier, t2->level_identifier) &&
+ t1->level_nr == t2->level_nr);
+}
+
+static void CopyTape(struct TapeInfo *tape_from, struct TapeInfo *tape_to)
+{
+ *tape_to = *tape_from;
+}
+
+static void SwapTapes(struct TapeInfo *t1, struct TapeInfo *t2)
+{
+ struct TapeInfo tmp = *t1;
+
+ *t1 = *t2;
+ *t2 = tmp;
+}
+
+static void CopyTapeToUndoBuffer(void)
+{
+ // copy tapes to undo buffer if large enough (or larger than last undo tape)
+ // or if the last undo tape is from a different level set or level number
+ if (tape.length_seconds >= TAPE_MIN_SECONDS_FOR_UNDO_BUFFER ||
+ tape.length_seconds >= tape_undo_buffer.length_seconds ||
+ !checkTapesFromSameLevel(&tape, &tape_undo_buffer))
+ {
+ CopyTape(&tape, &tape_undo_buffer);
+ }
+}
+
+void UndoTape(void)
+{
+ // only undo tapes from same level set and with same level number
+ if (!checkTapesFromSameLevel(&tape, &tape_undo_buffer))
+ return;
+
+ if (!TAPE_IS_STOPPED(tape))
+ TapeStop();
+
+ // swap last recorded tape with undo buffer, so undo can be reversed
+ SwapTapes(&tape, &tape_undo_buffer);
+
+ DrawCompleteVideoDisplay();
+}
+