From 02df82ca31b055452c2d1e6c5101f98eda1d8d70 Mon Sep 17 00:00:00 2001
From: sammik <samuelmiklas@gmail.com>
Date: Mon, 21 Oct 2024 02:33:04 +0200
Subject: [PATCH] Handle instrument changes

---
 src/engraving/dom/edit.cpp | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/engraving/dom/edit.cpp b/src/engraving/dom/edit.cpp
index 21d84aefe8d5c..0461199602780 100644
--- a/src/engraving/dom/edit.cpp
+++ b/src/engraving/dom/edit.cpp
@@ -2789,7 +2789,22 @@ void Score::deleteItem(EngravingItem* el)
         // remove section break key signatures
         bool isFirst = mb && mb->tick().isZero();
         for (KeySig* ks : lb->keySigs()) {
-            if (isFirst) {
+            Staff* staff = ks->staff();
+            Fraction tick = ks->tick();
+            KeySigEvent actualKey = ks->keySigEvent();
+            KeySigEvent prevKey = staff->prevKey(tick);
+
+            // do not remove keysig on first measure, or if signatures differ
+
+            // if previous signature is "forInstrumentChange",
+            // comparation returns false, even if they are otherwise identical
+            // (because one is forInstrumentChange and second not)
+            // so we need to remove "forInstrumentChange" flag first
+            if (prevKey.forInstrumentChange()) {
+                prevKey.setForInstrumentChange(false);
+            }
+
+            if (isFirst || actualKey != prevKey) {
                 ks->setForSectionBreak(false);
             } else {
                 deleteItem(ks);
@@ -6037,13 +6052,13 @@ void Score::undoAddElement(EngravingItem* element, bool addToLinkedStaves, bool
             MeasureBase* m = lb->measure();
 
             // add Key Signature on Section Break
-            // TODO: special case for instrument change
             Fraction tick = m->endTick();
             int ticks = tick.ticks();
             for (Staff* staff : score()->staves()) {
                 KeyList* kl = staff->keyList();
-                if (kl->currentKeyTick(ticks) != ticks) {
-                    KeySigEvent ks = kl->key(ticks);
+                KeySigEvent ks = kl->key(ticks);
+                if (kl->currentKeyTick(ticks) != ticks || ks.forInstrumentChange()) {
+                    ks.setForInstrumentChange(false);
                     ks.setForSectionBreak(true);
                     undoChangeKeySig(staff, tick, ks);
                 }