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, 5 insertions, 0 deletions

diff --git a/opl/opl.h b/opl/opl.h
index f0879b4d..d6a295b0 100644
--- a/opl/opl.h
+++ b/opl/opl.h
@@ -104,6 +104,11 @@ void OPL_InitRegisters(void);
 
 void OPL_SetCallback(unsigned int ms, opl_callback_t callback, void *data);
 
+// Adjust callback times by the specified factor. For example, a value of
+// 0.5 will halve all remaining times.
+
+void OPL_AdjustCallbacks(float factor);
+
 // Clear all OPL callbacks that have been set.
 
 void OPL_ClearCallbacks(void);