Allow -ve framepos handling in TempoMap::framepos_plus_beats()

	- also handles frame positions previous to the initial
	  meter (beat_at_frame() would return 0 in this case).

diff --git a/libs/ardour/tempo.cc b/libs/ardour/tempo.cc
index 56f88d33d9d6b080ccaab9e837afef4b422c91f6..11da2fc81d3892768dbc2efbd2c17bc439228465 100644 (file)
--- a/libs/ardour/tempo.cc
+++ b/libs/ardour/tempo.cc
@@ -3799,11 +3799,32 @@ TempoMap::remove_time (framepos_t where, framecnt_t amount)
  *  pos can be -ve, if required.
  */
 framepos_t
-TempoMap::framepos_plus_beats (framepos_t pos, Evoral::Beats beats) const
+TempoMap::framepos_plus_beats (framepos_t frame, Evoral::Beats beats) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       return frame_at_beat_locked (_metrics, beat_at_frame_locked (_metrics, pos) + beats.to_double());
+       const TempoSection& ts = tempo_section_at_frame_locked (_metrics, frame);
+       MeterSection* prev_m = 0;
+       MeterSection* next_m = 0;
+
+       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+               if (!(*i)->is_tempo()) {
+                       if (prev_m && (*i)->frame() > frame) {
+                               next_m = static_cast<MeterSection*> (*i);
+                               break;
+                       }
+                       prev_m = static_cast<MeterSection*> (*i);
+               }
+       }
+
+       double pos_beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
+
+       /* audio locked meters fake their beat */
+       if (next_m && next_m->beat() < pos_beat) {
+               pos_beat = next_m->beat();
+       }
+
+       return frame_at_beat_locked (_metrics, pos_beat + beats.to_double());
 }
 
 /** Subtract some (fractional) beats from a frame position, and return the result in frames */