shithub: patch

ref: 20557a701a58427918a503d97c0fcd7f4756b4f7
dir: /midi-dobend/

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midi: implement pitch wheel

this is an aborted attempt to implement pitch bending (event 0xe0).

this maintains a list of active notes, storing note number, amplitude and bent
frequency; this greatly reduces cpu time spent in run(), also alleviating the
issue of delays between writes to /dev/audio being too great...

it blows chunks:
- greatly complexifies midi note handling
- pitch steps are discrete and too noticeable, actually worsening playback
  (blatant example: doom e2m2), but don't yet know where T % f >= f/2 is coming
  from or how to fix this

→ i don't yet know what i'm doing nor how to solve this correctly

diff -r 9c4b9c67ff16 sys/src/games/midi.c
--- a/sys/src/games/midi.c	Thu Feb 16 20:11:20 2017 +0100
+++ b/sys/src/games/midi.c	Wed Feb 22 01:34:39 2017 +0200
@@ -3,19 +3,29 @@
 
 enum { SAMPLE = 44100 };
 
+typedef struct Note Note;
+typedef struct Tracker Tracker;
+
+struct Note {
+	int nt;
+	Tracker *src;
+	int ch;
+	uchar a;
+	int f;
+	int ½f;
+	Note *n;
+} nl[256], np;
+
 struct Tracker {
 	uchar *data;
 	char ended;
 	uvlong t;
-	uchar notes[16][128];
+	double bend[16];
 	int cmd;
 } *tr;
 
-typedef struct Tracker Tracker;
-
 int fd, ofd, div, tempo = 500000, ntrack;
 uvlong T;
-int freq[128];
 
 void *
 emallocz(int size)
@@ -108,32 +118,23 @@
 }
 
 void
-run(uvlong n)
+run(uvlong dt)
 {
-	int samp, j, k, l, no[128];
+	int samp, l;
 	uchar *s;
-	int t, f;
+	int t;
 	short u;
-	Tracker *x;
-	
-	samp = n - T;
+	Note *n;
+
+	samp = dt - T;
 	if(samp <= 0)
 		return;
-	memset(no, 0, sizeof no);
-	for(x = tr; x < tr + ntrack; x++){
-		if(x->ended)
-			continue;
-		for(j = 0; j < 16; j++)
-			for(k = 0; k < 128; k++)
-				no[k] += x->notes[j][k];
-	}
 	s = emallocz(samp * 4);
 	for(l = 0; l < samp; l++){
 		t = 0;
-		for(k = 0; k < 128; k++){
-			f = (T % freq[k]) >= freq[k]/2 ? 1 : 0;
-			t += f * no[k];
-		}
+		for(n = np.n; n != &np; n = n->n)
+			if(T % n->f >= n->½f)
+				t += n->a;
 		u = t*10;
 		s[4 * l] = s[4 * l + 2] = u;
 		s[4 * l + 1] = s[4 * l + 3] = u >> 8;
@@ -144,11 +145,70 @@
 }
 
 void
+bend(Tracker *src, int ch, int b)
+{
+	int f;
+	double d;
+	Note *n;
+
+	d = (b - 8192) / 4095.5;
+	d = pow(2, d / 12);
+	src->bend[ch] = d;
+	for(n = np.n; n != &np; n = n->n){
+		if(n->src != src || n->ch != ch)
+			continue;
+		f = SAMPLE / (440 * d * pow(1.05946, n->nt - 69));
+		n->f = f;
+		n->½f = f / 2;
+	}
+}
+
+void
+pop(Tracker *src, int ch, int nt)
+{
+	Note *n, *p;
+
+	for(p = &np, n = np.n; n != &np; p = n, n = n->n)
+		if(n->src == src && n->ch == ch && n->nt == nt){
+			p->n = n->n;
+			memset(n, 0, sizeof *n);
+			return;
+		}
+}
+
+void
+push(Tracker *src, int ch, int nt, int a)
+{
+	int f;
+	Note *n, *p;
+
+	for(p = &np, n = np.n; n != &np; p = n, n = n->n)
+		if(n->src == src && n->ch == ch && n->nt == nt){
+			n->a = a;
+			return;
+		}
+	for(n = nl; n < nl + nelem(nl); n++)
+		if(n->src == nil)
+			break;
+	if(n == nl + nelem(nl))
+		return;
+	n->src = src;
+	n->ch = ch;
+	n->nt = nt;
+	n->a = a;
+	f = SAMPLE / (440 * src->bend[ch] * pow(1.05946, nt - 69));
+	n->f = f;
+	n->½f = f / 2;
+	p->n = n;
+	n->n = &np;
+}
+
+void
 readevent(Tracker *src)
 {
 	uvlong l;
 	int n,t;
-	
+
 	l = tconv(getvar(src));
 	run(src->t += l);
 	t = get8(src);
@@ -161,13 +221,12 @@
 		src->cmd = t;
 	switch(t >> 4){
 	case 0x8:
-		n = get8(src);
+		pop(src, t & 15, get8(src));
 		get8(src);
-		src->notes[t & 15][n] = 0;
 		break;
 	case 0x9:
 		n = get8(src);
-		src->notes[t & 15][n] = get8(src);
+		push(src, t & 15, n, get8(src));
 		break;
 	case 0xB:
 		get16(src);
@@ -175,6 +234,11 @@
 	case 0xC:
 		get8(src);
 		break;
+	case 0xE:
+		n = get8(src) & 0x7f;
+		n = get8(src) << 7 & 0x3f80 | n;
+		bend(src, t & 15, n);
+		break;
 	case 0xF:
 		t = get8(src);
 		n = get8(src);
@@ -204,7 +268,7 @@
 void
 main(int argc, char **argv)
 {
-	int i, size;
+	int i, j, size;
 	uvlong t, mint;
 	Tracker *x, *minx;
 
@@ -228,9 +292,10 @@
 		size = get32(nil);
 		tr[i].data = emallocz(size);
 		read(fd, tr[i].data, size);
+		for(j = 0; j < 16; j++)
+			tr[i].bend[j] = 1.0;
 	}
-	for(i = 0; i < 128; i++)
-		freq[i] = SAMPLE / (440 * pow(1.05946, i - 69));
+	np.n = &np;
 	for(;;){
 		minx = nil;
 		mint = 0;