Fix unnecessary notehead separation for unison notes of different durations

src/engraving/dom/note.h

@@ -300,6 +300,8 @@ class Note final : public EngravingItem
 
     bool hidden() const { return m_hidden; }
     void setHidden(bool val) { m_hidden = val; }
+    bool hideNotehead() const { return m_hideNotehead; }
+    void setHideNotehead(bool val) { m_hideNotehead = val; }
     bool dotsHidden() const { return m_dotsHidden; }
     void setDotsHidden(bool val) { m_dotsHidden = val; }
 
@@ -494,6 +496,8 @@ class Note final : public EngravingItem
     bool m_hidden = false;                 // marks this note as the hidden one if there are
                                            // overlapping notes; hidden notes are not played
                                            // and heads + accidentals are not shown
+    bool m_hideNotehead = false;      // hides notehead glyph only for unison sharing;
+                                      // unlike m_hidden, does not affect playback or accidentals
     bool m_dotsHidden = false;        // dots of hidden notes are hidden too
                                       // except if only one note is dotted
     bool m_fretConflict = false;      // used by TAB staves to mark a fretting conflict:

src/engraving/rendering/score/chordlayout.cpp

@@ -1992,12 +1992,28 @@ void ChordLayout::calculateChordOffsets(Segment* segment, staff_idx_t staffIdx,
                     // thus user can force notes to be shared despite differing number of dots or either being stemless
                     // by setting one of the notehead types to match the other or by making one notehead invisible
                     // TODO: consider adding a style option, staff properties, or note property to control sharing
-                    if ((nchord->dots() != pchord->dots() || !nchord->stem() || !pchord->stem() || nHeadType != pHeadType
+
+                    // check if the notes are unison
+                    bool unisonMatch = (n->pitch() == p->pitch() && n->tpc() == p->tpc());
+
+                    // for unisons we allow half noteheads to merge even with different durations,
+                    // as the stem, flag, or beam makes the duration clear.
+                    // dotted notes can also merge with non-dotted notes at unison.
+                    if (((!unisonMatch && nchord->dots() != pchord->dots()) || !nchord->stem() || !pchord->stem()
+                         || (nHeadType != pHeadType && !unisonMatch)
                          || n->isSmall() || p->isSmall())
                         && ((n->headType() == NoteHeadType::HEAD_AUTO && p->headType() == NoteHeadType::HEAD_AUTO)
                             || nHeadType != pHeadType)
                         && (n->visible() == p->visible())) {
                         shareHeads = false;
+                    } else if (nHeadType != pHeadType && unisonMatch) {
+                        // ensure if a unison includes an open notehead this is shown in
+                        // preference to a filled notehead
+                        if (nHeadType == NoteHeadType::HEAD_QUARTER) {
+                            n->setHideNotehead(true);
+                        } else if (pHeadType == NoteHeadType::HEAD_QUARTER) {
+                            p->setHideNotehead(true);
+                        }
                     }
                 }
 
@@ -2381,6 +2397,7 @@ double ChordLayout::layoutChords2(std::vector<Note*>& notes, bool up, LayoutCont
         // by default, notes and dots are not hidden
         // this may be changed later to allow unisons to share noteheads
         note->setHidden(false);
+        note->setHideNotehead(false);
         note->setDotsHidden(false);
 
         // be sure chord position is initialized

src/engraving/rendering/score/tlayout.cpp

@@ -4137,7 +4137,7 @@ void TLayout::layoutNote(const Note* item, Note::LayoutData* ldata)
             const_cast<Note*>(item)->setHeadGroup(NoteHeadGroup::HEAD_DIAMOND);
         }
 
-        SymId nh = item->noteHead();
+        SymId nh = item->hideNotehead() ? SymId::noSym : item->noteHead();
         ldata->cachedNoteheadSym.set_value(nh);
 
         if (item->isNoteName()) {