add initial step sequencer implementation

sequencer/combine_seq.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "simple_seq.h"
+
+namespace trnr {
+
+struct combine_note {
+	int probability;
+	int pitch;
+	int octave;
+	int velocity;
+};
+
+struct combine_seq {
+	simple_seq probability_seq;
+	simple_seq pitch_seq;
+	simple_seq octave_seq;
+	simple_seq velocity_seq;
+	combine_note current_note;
+};
+
+inline void combine_seq_init(combine_seq& c, size_t max_len)
+{
+	simple_seq_init(c.probability_seq, max_len);
+	simple_seq_init(c.pitch_seq, max_len);
+	simple_seq_init(c.octave_seq, max_len);
+	simple_seq_init(c.velocity_seq, max_len);
+}
+
+inline combine_note& combine_seq_process_step(combine_seq& c)
+{
+	c.current_note.probability = simple_seq_process_step(c.probability_seq);
+	c.current_note.pitch = simple_seq_process_step(c.pitch_seq);
+	c.current_note.octave = simple_seq_process_step(c.octave_seq);
+	c.current_note.velocity = simple_seq_process_step(c.velocity_seq);
+
+	return c.current_note;
+}
+
+struct timing_info {};
+} // namespace trnr