#!/usr/bin/env ruby
#
# Script to investigate priorities of different MIDI instruments,
# so that the factor used to determine priority can be identified.
#
# We go through each pair of MIDI instruments, ie. (0, 1), (1, 2), ...
# etc. We then set channel 1 and 2 to use each of the instruments.
# Then we play enough notes (9) to fill every OPL voice, so that the
# allocated voices linked list looks like this:
#
# (start)-> 1-2-1-1-1-1-1-1-1
#
# Once all voices are filled, try to play a note on channel 2.  If
# channel 2 is a higher priority than channel 1, the first voice
# in the list (using channel 1) will be discarded for the new voice,
# but if channel 1 is a higher priority, the existing channel 2
# voice will be discarded to keep the channel 1 voice.
#
# From this we can work out how the priority of different instruments
# compares, and compare this to the instrument data to see if something
# fits.

def note_on(delay, channel, note, volume)
    # note on
    putc delay
    putc 0x90 + channel
    putc note
    putc volume
end

def note_off(delay, channel, note)
    # note on
    putc delay
    putc 0x80 + channel
    putc note
    putc 0x00
end

def program_change(delay, channel, instrument)
    putc delay
    putc 0xc0 + channel
    putc instrument
end

def end_of_track
    putc 0x00
    putc 0xff
    putc 0x2f
    putc 0x00
end

# Turn off the note in e1m1-cropped.mid

note_off(0, 2, 40)

# Go through each pair in turn.

for i in 0..32

    # Set the instruments for the two channels.

    program_change(0x1, 1, i)
    program_change(0x1, 2, i + 1)

    # Play some notes.

    note_on(0xf, 1, 0x40, 0x40)
    note_on(0xf, 1, 0x41, 0x40)
    note_on(0xf, 1, 0x42, 0x40)
    note_on(0xf, 1, 0x43, 0x40)
    note_on(0xf, 1, 0x44, 0x40)
    note_on(0xf, 1, 0x45, 0x40)
    note_on(0xf, 1, 0x46, 0x40)
    note_on(0xf, 2, 0x47, 0x40)
    note_on(0xf, 1, 0x48, 0x40)

    # The overflow note:

    note_on(0xf, 2, 0x49, 0x40)

    # Turn off all the notes:

    note_off(0xf, 1, 0x40)
    note_off(0xf, 1, 0x41)
    note_off(0xf, 1, 0x42)
    note_off(0xf, 1, 0x43)
    note_off(0xf, 1, 0x44)
    note_off(0xf, 1, 0x45)
    note_off(0xf, 1, 0x46)
    note_off(0xf, 2, 0x47)
    note_off(0xf, 1, 0x48)
    note_off(0xf, 2, 0x49)
end

end_of_track