player.pseudocode

#    oStartOfOrders
#    |               oStartOfPatterns
#    |               |
#    |   order       |   patterns  / -- line ---
#    '-> 00 01 02    '-> 00 ------/ --- line  |  - pos = 3
#        00 01 03        |_______|\ --- line ---
#        04 05 02                  \ -- line
#        06 07 03
#                                  / -- line ---
#                        01 ------/ --- line  |  - pos = 3
#                        |_______|\ --- line ---
#                                  \ -- line
#                        ...
#

# constants
kNumLinesInPattern	equ	32
kNumBytesInLine		equ	5
oNumChannels		equ	offset of field containing number of channels
oStartOfOrders		equ	offset of field containing offset of first order
oStartOfPatterns	equ	offset of field containing offset of first pattern

# variables updated at song load
aSong		dw	address at which song is loaded
numChannels:	db	0

# variables updated at play time
state:		db	play/stop
order:		dw	0
pos:		db	0


Init/reset song:
	pos = 0
	numChannels = [aSong + oNumChannels]
	order = [aSong + oStartOfOrders] + aSong
	if order == [aSong + oStartOfPatterns] + aSong:
		the song is zero-length: quit now

Play a line:
	for channel=0; channel<numChannels; channel++:
		pattern_num = [order + channel]
		pattern = [aSong + oStartOfPatterns] + pattern_num*kNumLinesInPattern*kNumBytesInLine
		line = [pattern + (pos * kNumBytesInLine)]
		make channel play line:
			if there is a note here:
				Stash line (channel)
				Noteon (channel)	# (uses stashed current line of this channel)
				#TODO left off here - test as-is before adding detailed play goo

	# move on to next line
	pos += 1

	# move on to next order if we're at the end of this one
	if pos == kNumLinesInPattern:
		pos = 0
		order += kNumChannels

		# loop to start of song if we're out of orders
		if order == [aSong + oStartOfPatterns] + aSong:
			order = [aSong + oStartOfOrders] + aSong

Tick:
	If state == playing:	
		if ticks % speed == 0:
			Play a line()

		for channel=0; channel<numChannels; channel++:
			Effects tick (channel)	# (uses stashed current line of this channel)
			SpFx tick (channel)	# (ditto, figure this out later)
			#TODO left off here - should probably test as-is before adding detailed play goo

		ticks++