freedoom/lumps/genmidi/genmidi.py

#!/usr/bin/env python
# SPDX-License-Identifier: BSD-3-Clause
#
# Module for interacting with Doom GENMIDI lumps.
#

from instrument import Instrument, NullInstrument
import struct
import sys

GENMIDI_HEADER = "#OPL_II#"
NUM_INSTRUMENTS = 175
INSTR_DATA_LEN = 36
INSTR_NAME_LEN = 32

FLAG_FIXED_PITCH = 0x0001
FLAG_TWO_VOICE   = 0x0004

KSL_MASK = 0xc0
VOLUME_MASK = 0x3f

# Order of fields in GENMIDI data structures.

GENMIDI_FIELDS = [
	"m_am_vibrato_eg",
	"m_attack_decay",
	"m_sustain_release",
	"m_waveform",
	"m_ksl",
	"m_volume",
	"feedback_fm",
	"c_am_vibrato_eg",
	"c_attack_decay",
	"c_sustain_release",
	"c_waveform",
	"c_ksl",
	"c_volume",
	"null",
	"note_offset"
]

# Encode a single voice of an instrument to binary.

def encode_voice(data, offset):
	result = dict(data)

	result["m_ksl"] = data["m_ksl_volume"] & KSL_MASK
	result["m_volume"] = data["m_ksl_volume"] & VOLUME_MASK
	result["c_ksl"] = data["c_ksl_volume"] & KSL_MASK
	result["c_volume"] = data["c_ksl_volume"] & VOLUME_MASK

	result["null"] = 0
	result["note_offset"] = offset

	return struct.pack("<BBBBBBBBBBBBBBh",
	                   *map(lambda key: result[key], GENMIDI_FIELDS))

# Encode an instrument to binary.

def encode_instrument(instrument):
	flags = 0

	instr1_data = encode_voice(instrument.voice1, instrument.offset1)

	if instrument.voice2 is not None:
		flags |= FLAG_TWO_VOICE
		instr2_data = encode_voice(instrument.voice2,
		                           instrument.offset2)
	else:
		instr2_data = encode_voice(NullInstrument.voice1, 0)

	if instrument.fixed_note is not None:
		flags |= FLAG_FIXED_PITCH
		fixed_note = instrument.fixed_note
	else:
		fixed_note = 0

	header = struct.pack("<hBB", flags, 128, fixed_note)

	return header + instr1_data + instr2_data

def encode_instruments(instruments):
	result = []

	for instrument in instruments:
		result.append(encode_instrument(instrument))

	return b"".join(result)

def encode_instrument_names(instruments):
	result = []

	for instrument in instruments:
		instr_name = instrument.voice1["name"].encode("ascii")
		result.append(struct.pack("32s", instr_name))

	return b"".join(result)

def write(filename, instruments):
	header = struct.pack("%is" % len(GENMIDI_HEADER),
	                     GENMIDI_HEADER.encode("ascii"))

	with open(filename, "wb") as f:
		f.write(header)
		f.write(encode_instruments(instruments))
		f.write(encode_instrument_names(instruments))

def decode_voice(data, name):

	fields = struct.unpack("<BBBBBBBBBBBBBBh", data)

	result = {}
	for i in range(len(GENMIDI_FIELDS)):
		result[GENMIDI_FIELDS[i]] = fields[i]

	result["m_ksl_volume"] = result["m_ksl"] | result["m_volume"]
	result["c_ksl_volume"] = result["c_ksl"] | result["c_volume"]
	result["name"] = name.decode("ascii").rstrip("\0")

	return result

def decode_instrument(data, name):
	flags, finetune, fixed_note = struct.unpack("<hBB", data[0:4])

	voice1 = decode_voice(data[4:20], name)
	offset1 = voice1["note_offset"]

	# Second voice?

	if (flags & FLAG_TWO_VOICE) != 0:
		voice2 = decode_voice(data[20:], name)
		offset2 = voice2["note_offset"]
	else:
		voice2 = None
		offset2 = 0

	# Null out fixed_note if the fixed pitch flag isn't set:

	if (flags & FLAG_FIXED_PITCH) == 0:
		fixed_note = None

	return Instrument(voice1, voice2,
	                  off1=offset1, off2=offset2,
	                  note=fixed_note)

def read(filename):
	with open(filename, "rb") as f:
		data = f.read()

	# Check header:

	header = data[0:len(GENMIDI_HEADER)]
	if header.decode("ascii") != GENMIDI_HEADER:
		raise Exception("Incorrect header for GENMIDI lump")

	body = data[len(GENMIDI_HEADER):]
	instr_data = body[0:NUM_INSTRUMENTS * INSTR_DATA_LEN]
	instr_names = body[NUM_INSTRUMENTS * INSTR_DATA_LEN:]
	result = []

	for i in range(NUM_INSTRUMENTS):
		data = instr_data[i * INSTR_DATA_LEN:(i+1) * INSTR_DATA_LEN]
		name = instr_names[i * INSTR_NAME_LEN:(i+1) * INSTR_NAME_LEN]

		result.append(decode_instrument(data, name))

	return result

if __name__ == "__main__":
	for filename in sys.argv[1:]:
		instruments = read(filename)
		for i in range(len(instruments)):
			instrument = instruments[i]
			fixed_note = instrument.fixed_note

			if fixed_note is not None:
				print("%i (fixed note: %i):" % (i, fixed_note))
			else:
				print("%i:" % i)

			print("\tVoice 1: %s" % instrument.voice1)
			if instrument.voice2 is not None:
				print("\tVoice 2: %s" % instrument.voice2)