Fret Limit

generator/fretboard.py

@@ -11,6 +11,7 @@ import generator.pitch
 STANDARD_TUNING = ((6, 40), (5, 45), (4, 50), (3, 55), (2, 59), (1, 64))
 MIN_FRET = 1
 MAX_FRET = 20
+MAX_SINGLE_FRET = 12
 MAX_FRET_SPAN = 3
 MAX_ANCHOR_FRET = 12
 WRITTEN_GUITAR_OCTAVE_OFFSET = 12
@@ -33,6 +34,48 @@ def positions_for_pitch(midi: fractions.Fraction) -> tuple[TabPosition, ...]:
     return ()
   return tuple(TabPosition(string, int(midi - open_midi), int(midi)) for string, open_midi in STANDARD_TUNING if MIN_FRET <= midi - open_midi <= MAX_FRET)
 
+def single_positions_for_pitch(midi: fractions.Fraction) -> tuple[TabPosition, ...]:
+  return tuple(p for p in positions_for_pitch(midi) if p.fret <= MAX_SINGLE_FRET)
+
+def single_register(register: tuple[int, int]) -> tuple[int, int]:
+  return max(register[0], min(p + MIN_FRET for _, p in STANDARD_TUNING)), min(register[1], max(p + MAX_SINGLE_FRET for _, p in STANDARD_TUNING))
+
+def playable_attack(tones) -> bool:
+  """Check a played note/chord, including tails after shorter tones release.
+
+  Each item is a (position, sounding duration) pair. Independent parts and
+  unsounded members of an underlying grip cannot supply the chord's anchor.
+  """
+  tones = tuple(tones)
+  for time in {0, *(duration for _, duration in tones if duration > 0)}:
+    positions = tuple(p for p, duration in tones if duration > time or time == duration == 0)
+    if not positions:
+      continue
+    if any(p not in positions_for_pitch(fractions.Fraction(p.midi)) for p in positions) or len({p.string_number for p in positions}) != len(positions) or not within_fret_span(positions):
+      return False
+    if len(positions) == 1:
+      if positions[0].fret > MAX_SINGLE_FRET:
+        return False
+    elif not has_fret_anchor(positions):
+      return False
+  return True
+
+def validate_document(document: dict) -> None:
+  """Validate generated guitar policy separately from the score wire format."""
+  for staff in document['staves']:
+    if not staff.get('tablature'):
+      continue
+    for measure in staff['measures']:
+      for voice in measure['voices']:
+        for note in voice['notes']:
+          tones = []
+          for pitch in note['pitches']:
+            tab = pitch['tablature']
+            position = TabPosition(tab['string'], tab['fret'], dict(STANDARD_TUNING)[tab['string']] + tab['fret'])
+            tones.append((position, generator.model.fraction(pitch['duration'])))
+          if not playable_attack(tones):
+            raise ValueError(f'{measure["id"]}, event {note["id"]}: single notes require frets {MIN_FRET}-{MAX_SINGLE_FRET}; each sounding chord requires an anchor in {MIN_FRET}-{MAX_ANCHOR_FRET} and at most {MAX_FRET_SPAN} consecutive fret positions, including held/tied tails')
+
 def validate_tuning(state: dict, location: str) -> None:
   details = state['staff_details']
   if details.get('capo', 0):