opl: Add API to adjust tempo.

When the tempo is changed, the times on all active timers must be
adjusted to match the new timing values. Add an API to do this and
invoke it when a tempo change meta event is read.

1 files changed, 12 insertions, 6 deletions

diff --git a/src/i_oplmusic.c b/src/i_oplmusic.c
index f38e7162..489b6d55 100644
--- a/src/i_oplmusic.c
+++ b/src/i_oplmusic.c
@@ -1016,6 +1016,12 @@ static void PitchBendEvent(opl_track_data_t *track, midi_event_t *event)
     }
 }
 
+static void MetaSetTempo(unsigned int tempo)
+{
+    OPL_AdjustCallbacks((float) us_per_beat / tempo);
+    us_per_beat = tempo;
+}
+
 // Process a meta event.
 
 static void MetaEvent(opl_track_data_t *track, midi_event_t *event)
@@ -1041,7 +1047,7 @@ static void MetaEvent(opl_track_data_t *track, midi_event_t *event)
         case MIDI_META_SET_TEMPO:
             if (data_len == 3)
             {
-                us_per_beat = (data[0] << 16) | (data[1] << 8) | data[2];
+                MetaSetTempo((data[0] << 16) | (data[1] << 8) | data[2]);
             }
             break;
 
@@ -1168,19 +1174,19 @@ static void TrackTimerCallback(void *arg)
 static void ScheduleTrack(opl_track_data_t *track)
 {
     unsigned int nticks;
-    unsigned int ms;
-    static int total = 0;
+    uint64_t ms;
 
     // Get the number of milliseconds until the next event.
 
     nticks = MIDI_GetDeltaTime(track->iter);
-    ms = (nticks * us_per_beat * TEMPO_FUDGE_FACTOR) / ticks_per_beat;
-    total += ms;
+    ms = nticks;
+    ms *= us_per_beat * TEMPO_FUDGE_FACTOR;
+    ms /= ticks_per_beat;
 
     // Set a timer to be invoked when the next event is
     // ready to play.
 
-    OPL_SetCallback(ms, TrackTimerCallback, track);
+    OPL_SetCallback((unsigned int) ms, TrackTimerCallback, track);
 }
 
 // Initialize a channel.