1 files changed, 75 insertions, 0 deletions
diff --git a/musiclib.nim b/musiclib.nim
new file mode 100644
index 0000000..c21cb95
--- /dev/null
+++ b/musiclib.nim
@@ -0,0 +1,75 @@
+import std/[algorithm, math, sugar, strformat, logging]
+
+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
+    if ret >= int32.high.float:
+        warn(&"audio clipping at t={t}")
+        int32.high
+    elif ret <= int32.low.float:
+        warn(&"audio clipping at t={t}")
+        int32.low
+    else:
+        int32(ret)