oplmusic: Handle key-on with volume 0 as key-off.

Some MIDI files, such as the music tracks in AV.wad, use a second
"key on" event with a volume of zero to mean "key off". Handle this
case correctly.

1 files changed, 12 insertions, 3 deletions

diff --git a/src/i_oplmusic.c b/src/i_oplmusic.c
index c07146a7..a2bc22d8 100644
--- a/src/i_oplmusic.c
+++ b/src/i_oplmusic.c
@@ -881,12 +881,21 @@ static void KeyOnEvent(opl_track_data_t *track, midi_event_t *event)
            event->data.channel.param2);
 */
 
-    // The channel.
-
-    channel = &track->channels[event->data.channel.channel];
     key = event->data.channel.param1;
     volume = event->data.channel.param2;
 
+    // A volume of zero means key off. Some MIDI tracks, eg. the ones
+    // in AV.wad, use a second key on with a volume of zero to mean
+    // key off.
+    if (volume <= 0)
+    {
+        KeyOffEvent(track, event);
+        return;
+    }
+
+    // The channel.
+    channel = &track->channels[event->data.channel.channel];
+
     // Percussion channel (10) is treated differently.
 
     if (event->data.channel.channel == 9)