Fix: EDx has complicated trigger rules.

Thanks @DanielOaks for noticing the issue.

README.md

@@ -144,7 +144,8 @@ they are supposed to test) is in the table below.
 -------------------------------+----------------+------------------------+------------------------------------------------
 amiga.xm                       | FAIL           | MilkyTracker, xmp      | Should sound identical.
 finetune.xm                    | PASS           | MilkyTracker           | Left and right channels should sound identical.
-ghost-note-delay.xm            | FAIL           | MilkyTracker           | Should sound identical.
+note-delay-ghost.xm            | PASS           | MilkyTracker, FT2      | Should sound identical.
+note-delay-retrig.xm           | PASS           | MilkyTracker           | Should sound identical.
 pattern-loop-quirk.xm          | PASS           | MilkyTracker           | Should play the same notes at the same time.
 ramping.xm                     | PASS           | MilkyTracker           | If XM_RAMPING is ON, no loud clicks should be heard.
 ramping2.xm                    | PASS           | MilkyTracker           | If XM_RAMPING is ON, no loud clicks should be heard.

src/play.c

@@ -446,7 +446,7 @@ static void xm_handle_note_and_instrument(xm_context_t* ctx, xm_channel_context_
 				ch->frame_count = 0;
 #endif
 				ch->sample = instr->samples + instr->sample_of_notes[s->note - 1];
-				ch->note = s->note + ch->sample->relative_note
+				ch->orig_note = ch->note = s->note + ch->sample->relative_note
 					+ ch->sample->finetune / 128.f - 1.f;
 				if(s->instrument > 0) {
 					xm_trigger_note(ctx, ch, 0);
@@ -672,7 +672,25 @@ static void xm_handle_note_and_instrument(xm_context_t* ctx, xm_channel_context_
 			break;
 
 		case 0xD: /* EDy: Note delay */
-			/* Already taken care of */
+			/* XXX: figure this out better. EDx triggers
+			 * the note even when there no note and no
+			 * instrument. But ED0 acts like like a ghost
+			 * note, EDx (x ≠ 0) does not. */
+			if(s->note == 0 && s->instrument == 0) {
+				unsigned int flags = XM_TRIGGER_KEEP_VOLUME;
+
+				if(ch->current->effect_param & 0x0F) {
+					ch->note = ch->orig_note;
+					xm_trigger_note(ctx, ch, flags);
+				} else {
+					xm_trigger_note(
+						ctx, ch,
+						flags
+						| XM_TRIGGER_KEEP_PERIOD
+						| XM_TRIGGER_KEEP_SAMPLE_POSITION
+						);
+				}
+			}
 			break;
 
 		case 0xE: /* EEy: Pattern delay */

src/xm_internal.h

@@ -154,6 +154,7 @@ struct xm_sample_s {
 
  struct xm_channel_context_s {
 	 float note;
+	 float orig_note; /* The original note before effect modifications, as read in the pattern. */
 	 xm_instrument_t* instrument; /* Could be NULL */
 	 xm_sample_t* sample; /* Could be NULL */
 	 xm_pattern_slot_t* current;