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import std/[algorithm, math, sugar, strformat]
type
OscFn* = proc (f: float, t: float): float
Note* = tuple
len: float ## seconds
freq: float
vol: float
osc: OscFn
ProcessedNote* = tuple
start: float ## absolute time in seconds
stop: float ## absolute time in seconds
freq: float
vol: float
osc: OscFn
const HACK_LONGEST_NOTE = 16.0
func process*(music: var seq[ProcessedNote], notes: openArray[Note]; start_init: float, speed: float=1) =
## Adds a list of notes to the music list
##
## `notes` sequence of notes with no rests in between
var start = start_init
var t = start
for note in notes:
assert note.len >= 0.0
assert note.len <= HACK_LONGEST_NOTE, &"note too long: {note.len}"
start = t
let stop = t + note.len / speed
music &= (start, stop, note.freq, note.vol, note.osc)
t = stop
func sortByStart*(music: var seq[ProcessedNote]) =
music.sort((a, b) => cmp(a.start, b.start))
func bisect(music: openArray[ProcessedNote], x: float): int =
## Return the index where to insert item `x` in list `music`
##
## assumes `music` is sorted by `.start`
music.lowerBound(x, (m, key) => cmp(m.start, key))
const GAIN_BIAS: float = pow(2.0, 31.0)
proc at*(music: openArray[ProcessedNote], t: float): int32 =
## Returns the total intensity of music sampled at time t
##
## assumes `music` is sorted by `.start`
var i: int = music.bisect(t) - 1
var ret: float = 0
while i >= 0:
let m = music[i]
assert m.start <= t
if m.start + HACK_LONGEST_NOTE < t:
break
else:
ret += m.vol * m.osc(m.freq, t - m.start)
i -= 1
ret *= GAIN_BIAS
# clip sample
clamp(ret, int32.low.float..int32.high.float).int32
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