temporal: change API for TempoMap::stretch_tempo()

This will likely be modified because it is actually impossible to do
what this code is attempting to do.

libs/temporal/tempo.cc

@@ -3180,6 +3180,103 @@ TempoMap::set_continuing (TempoPoint& tp, bool yn)
 	return true;
 }
 
+#if 1
+void
+TempoMap::stretch_tempo (TempoPoint& focus, double tempo_value)
+{
+	/* Our goal is to alter the outound tempo at @param focus and at the same
+	 * time create & modify a ramp between the previous tempo and @param focus
+	 * so that @param remains in the same location. 
+	 *
+	 * The user has placed @param focus at the correct point, but wanfocus to
+	 * adjust the (outbound) tempo without creating an obvious step change
+	 * at @param focus. So we want to ramp from prev to focus
+	 */
+
+	TempoPoint* prev = const_cast<TempoPoint*> (previous_tempo (focus));
+
+	TempoPoint old_prev (*prev);
+	TempoPoint old_focus (focus);
+
+	std::cerr << "using " << tempo_value << " working on " << focus << std::endl;
+	std::cerr << "\twith prev " << *prev << std::endl;
+
+	std::cerr << "focus then " << focus << std::endl;
+	focus.set_note_types_per_minute (tempo_value);
+	focus.set_end_npm (tempo_value);
+	std::cerr << "focus now " << focus << std::endl;
+	prev->set_end_npm (tempo_value);
+	prev->compute_omega_beats_from_next_tempo (focus);
+
+	superclock_t err = prev->superclock_at (focus.beats()) - focus.sclock();
+	const superclock_t one_sample = superclock_ticks_per_second() / TEMPORAL_SAMPLE_RATE;
+	const Beats b (focus.beats() - prev->beats());
+	// const double end_scpqn = focus.superclocks_per_quarter_note();
+	double scpqn = focus.superclocks_per_quarter_note ();
+	double new_npm;
+	int cnt = 0;
+
+	std::cerr << "initial error = " << err / (double) one_sample << std::endl;
+	reset_starting_at (prev->sclock());;
+	return;
+
+	while (std::abs(err) >= one_sample) {
+
+		if (err > 0) {
+			/* estimated > actual: speed end tempo up a little aka
+			   reduce scpqn
+			*/
+			scpqn *= 0.99;
+		} else {
+			/* estimated < actual: reduce end tempo a little, aka
+			   increase scpqn
+			*/
+			scpqn *= 1.01;
+		}
+
+		if (scpqn < 1.0) {
+			/* mathematically too small, bail out */
+			*prev = old_prev;
+			focus = old_focus;
+			return;
+		}
+
+		/* Convert scpqn to notes-per-minute */
+
+		new_npm = ((superclock_ticks_per_second() * 60.0) / scpqn) * (focus.note_type() / 4.0);
+
+		/* limit range of possible discovered tempo */
+
+		if (new_npm < 4.0 && new_npm > 400) {
+			/* too low of a tempo for our taste, bail out */
+			*prev = old_prev;
+			focus = old_focus;
+			return;
+		}
+
+		/* set the (initial) tempo, recompute omega and then compute
+		 * the (new) error (distance between the predicted position of
+		 * the next marker and its actual (fixed) position.
+		 */
+
+		focus.set_note_types_per_minute (new_npm);
+		focus.set_end_npm (new_npm);
+		prev->set_end_npm (new_npm);
+		prev->compute_omega_beats_from_next_tempo (focus);
+		err = prev->superclock_at (focus.beats()) - focus.sclock();
+		++cnt;
+	}
+
+	std::cerr << "that took " << cnt << " iterations to get to < 1 sample\n";
+	std::cerr << "final focus: " << focus << std::endl;
+	std::cerr << "final prev: " << *prev << std::endl;
+
+	reset_starting_at (prev->sclock());
+	// dump (std::cerr);
+}
+
+#else
+
 /* Adjusts the outgoing tempo at @p ts so that the next Tempo point is at @p
  * end_sample, while keeping the beat time positions of both the same.
  *
@@ -3259,6 +3356,9 @@ TempoMap::stretch_tempo (TempoPoint* ts, samplepos_t sample, samplepos_t end_sam
 
 		new_bpm = std::min (new_bpm, 1000.0);
 	}
+
+	std::cerr << "new bpm: " << new_bpm << std::endl;
+
 	/* don't clamp and proceed here.
 	   testing has revealed that this can go negative,
 	   which is an entirely different thing to just being too low.
@@ -3280,6 +3380,8 @@ TempoMap::stretch_tempo (TempoPoint* ts, samplepos_t sample, samplepos_t end_sam
 	reset_starting_at (ts->sclock() + 1);
 }
 
+#endif
+
 void
 TempoMap::stretch_tempo_end (TempoPoint* ts, samplepos_t sample, samplepos_t end_sample)
 {
@@ -3328,6 +3430,7 @@ TempoMap::stretch_tempo_end (TempoPoint* ts, samplepos_t sample, samplepos_t end
 
 	reset_starting_at (prev_t->sclock());
 }
+
 void
 TempoMap::twist_tempi (TempoPoint& prev, TempoPoint& focus, TempoPoint& next, double tempo_value)
 {

libs/temporal/temporal/tempo.h

@@ -766,7 +766,7 @@ class /*LIBTEMPORAL_API*/ TempoMap : public PBD::StatefulDestructible
 	LIBTEMPORAL_API int set_state (XMLNode const&, int version);
 
 	LIBTEMPORAL_API void twist_tempi (TempoPoint& prev, TempoPoint& focus, TempoPoint& next, double tempo_delta);
-	LIBTEMPORAL_API void stretch_tempo (TempoPoint* ts, samplepos_t sample, samplepos_t end_sample, Beats const & start_qnote, Beats const & end_qnote);
+	LIBTEMPORAL_API void stretch_tempo (TempoPoint& ts, double new_npm);
 	LIBTEMPORAL_API void stretch_tempo_end (TempoPoint* ts, samplepos_t sample, samplepos_t end_sample);
 
 	/* END OF MODIFYING METHODS */