Span

generator/fretboard.py

@@ -12,6 +12,7 @@ STANDARD_TUNING = ((6, 40), (5, 45), (4, 50), (3, 55), (2, 59), (1, 64))
 MIN_FRET = 1
 MAX_FRET = 20
 MAX_FRET_SPAN = 3
+MAX_ANCHOR_FRET = 12
 WRITTEN_GUITAR_OCTAVE_OFFSET = 12
 
 class TabPosition(typing.NamedTuple):
@@ -20,8 +21,12 @@ class TabPosition(typing.NamedTuple):
   midi: int
 
 def within_fret_span(positions) -> bool:
+  """Count occupied fret positions inclusively: frets 1-3 fit, 1-4 do not."""
   frets = [position.fret for position in positions]
-  return not frets or max(frets) - min(frets) <= MAX_FRET_SPAN
+  return not frets or max(frets) - min(frets) + 1 <= MAX_FRET_SPAN
+
+def has_fret_anchor(positions) -> bool:
+  return any(MIN_FRET <= position.fret <= MAX_ANCHOR_FRET for position in positions)
 
 def positions_for_pitch(midi: fractions.Fraction) -> tuple[TabPosition, ...]:
   if midi.denominator != 1: