instrument swap implemented (thanks to @Eknous-P)

src/engine/engine.cpp

@@ -3248,6 +3248,20 @@ bool DivEngine::moveSampleDown(int which) {
   return true;
 }
 
+bool DivEngine::swapInstruments(int a, int b) {
+  if (a<0 || a>=(int)song.ins.size() || b<0 || b>=(int)song.ins.size()) return false;
+  BUSY_BEGIN;
+  DivInstrument* temp=song.ins[a];
+  saveLock.lock();
+  song.ins[a]=song.ins[b];
+  song.ins[b]=temp;
+  moveAsset(song.insDir,a,b);
+  exchangeIns(a,b);
+  saveLock.unlock();
+  BUSY_END;
+  return true;
+}
+
 void DivEngine::autoPatchbay() {
   song.patchbay.clear();
   for (unsigned int i=0; i<song.systemLen; i++) {

src/engine/engine.h

@@ -1107,6 +1107,9 @@ class DivEngine {
     bool moveWaveDown(int which);
     bool moveSampleDown(int which);
 
+    // swap things
+    bool swapInstruments(int a, int b);
+
     // automatic patchbay
     void autoPatchbay();
     void autoPatchbayP();

src/gui/dataList.cpp

@@ -138,8 +138,10 @@ void FurnaceGUI::insListItem(int i, int dir, int asset) {
         const ImGuiPayload* payload=ImGui::AcceptDragDropPayload("FUR_INS");
         if (payload!=NULL) {
           int targetIns=i;
-          printf("From %d to %d\n",insToMove,targetIns);
-          // TODO: actually swap the instruments
+          if (insToMove!=targetIns && e->swapInstruments(insToMove,targetIns)) {
+            MARK_MODIFIED;
+            curIns=targetIns;
+          }
           insToMove=-1;
           ImGui::EndDragDropTarget();
         }