genmidi: Add constants for MIDI notes.

Constant definitions for MIDI notes, so that instrument definitions do
not need to use meaningless numbers.

lumps/genmidi/midi.py

@@ -0,0 +1,42 @@
+
+# Constants for MIDI notes.
+#
+# For example:
+#    F# in Octave 3:      O3.Fs
+#    C# in Octave -2:     On2.Cs
+#    D-flat in Octave 1:  O1.Db
+#    D in Octave 0:       O0.D
+#    E in Octave 2:       O2.E
+
+class Octave:
+	def __init__(self, base):
+		self.C  = base
+		self.Cs = base + 1
+		self.Db = base + 1
+		self.D  = base + 2
+		self.Ds = base + 3
+		self.Eb = base + 3
+		self.E  = base + 4
+		self.F  = base + 5
+		self.Fs = base + 6
+		self.Gb = base + 6
+		self.G  = base + 7
+		self.Gs = base + 8
+		self.Ab = base + 8
+		self.A  = base + 9
+		self.As = base + 10
+		self.Bb = base + 10
+		self.B  = base + 11
+
+On5 = Octave(0)      # Octave -5
+On4 = Octave(12)     # Octave -4
+On3 = Octave(24)     # Octave -3
+On2 = Octave(36)     # Octave -2
+On1 = Octave(48)     # Octave -1
+O0  = Octave(60)     # Octave 0
+O1  = Octave(72)     # Octave 1
+O2  = Octave(84)     # Octave 2
+O3  = Octave(96)     # Octave 3
+O4  = Octave(108)    # Octave 4
+O5  = Octave(120)    # Octave 5
+