From a7a42cfa20404b4fef52d4db6116344ec4c10656 Mon Sep 17 00:00:00 2001
From: Chris <chrisherb.sites@outlook.com>
Date: Fri, 28 Jul 2023 18:44:45 +0200
Subject: [PATCH] intial commit of retro buffer

---
 util/retro_buf.h | 154 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 util/retro_buf.h

diff --git a/util/retro_buf.h b/util/retro_buf.h
new file mode 100644
index 0000000..853e699
--- /dev/null
+++ b/util/retro_buf.h
@@ -0,0 +1,154 @@
+#pragma once
+
+#include "../filter/chebyshev.h"
+#include "../companding/ulaw.h"
+#include <iostream>
+
+namespace trnr {
+
+struct retro_buf_modulation {
+    double midi_note;
+    double pitch_mod;
+    double samplerate; // the (re)samplerate
+    double bitrate;
+    size_t start; // sets the start point from which to play
+    size_t end; // sets the end point
+    bool looping; // sets whether the sample should loop
+    bool reset; // resets the phase
+    int jitter; // jitter amount
+    double deviation;
+};
+
+// base class for accessing a sample buffer with adjustable samplerate, bitrate and other options.
+class retro_buf {
+public:
+    void set_host_samplerate(double _samplerate) {
+        m_host_samplerate = _samplerate;
+        m_imaging_filter_l.set_samplerate(_samplerate);
+        m_imaging_filter_r.set_samplerate(_samplerate);
+    }
+
+    void set_buf_samplerate(double _samplerate) {
+        m_buf_samplerate = _samplerate;
+    }
+
+    void set_buffer_size(size_t _buffer_size) {
+        m_buffer_size = _buffer_size;
+    }
+
+    void set_channel_count(size_t _channel_count) {
+        m_channel_count = _channel_count;
+    }
+
+    void start_playback() {
+        if (m_modulation.reset || (!m_modulation.reset && m_playback_pos == -1)) {
+            m_playback_pos = (double)m_modulation.start;
+        }
+    }
+
+    void process_block(double** _outputs, size_t _block_size, retro_buf_modulation _mod) {
+
+        m_modulation = _mod;
+
+        for (int i = 0; i < _block_size; ++i) {
+            double output_l = 0;
+            double output_r = 0;
+            
+            // if within bounds
+            if (m_playback_pos > -1 && m_playback_pos <= _mod.end)  {
+                
+                // quantize index
+                double samplerate_divisor = m_host_samplerate / _mod.samplerate;
+                size_t quantized_index = static_cast<size_t>(static_cast<size_t>(m_playback_pos / samplerate_divisor) * samplerate_divisor);
+
+                // get sample for each channel
+                output_l = get_sample((size_t)quantized_index, 0);
+                if (m_channel_count > 0) {
+                    output_r = get_sample(wrap(quantized_index + calc_jitter(_mod.jitter), m_buffer_size), 1);
+                } else {
+                    output_r = output_l;
+                }
+                
+                // advance position
+                double note_ratio = midi_to_ratio(_mod.midi_note + _mod.pitch_mod);
+                m_playback_pos += note_ratio * (m_buf_samplerate / m_host_samplerate);
+            
+                reduce_bitrate(output_l, output_r, _mod.bitrate);
+
+                // calculate imaging filter frequency + deviation
+                double filter_frequency = ((_mod.samplerate / 2) * note_ratio) * _mod.deviation;
+
+                m_imaging_filter_l.process_sample(output_l, filter_frequency);
+                m_imaging_filter_r.process_sample(output_r, filter_frequency);
+            }
+            // else if loop
+            else if(_mod.looping) {
+                // loop
+                m_playback_pos = (double)_mod.start;
+            }
+            // else
+            else {
+                // stop
+                m_playback_pos = -1;
+            }
+
+            _outputs[0][i] = output_l;
+            _outputs[1][i] = output_r;
+            _outputs[2][i] = (double)_mod.end;
+        }
+    }
+
+    virtual float get_sample(size_t _index, size_t _channel) = 0;
+
+private:
+    size_t m_channel_count = 0;
+    size_t m_buffer_size = 0;
+    double m_buf_samplerate = 44100.0;
+    double m_host_samplerate = 44100.0;
+    double m_playback_pos = -1;
+
+    chebyshev m_imaging_filter_l;
+    chebyshev m_imaging_filter_r;
+    ulaw m_compander;
+    retro_buf_modulation m_modulation;
+
+    float midi_to_ratio(double midi_note) {
+        return powf(powf(2, (float)midi_note - 60.f), 1.f / 12.f);
+    }
+    
+    template <typename T>
+    T clamp(T& value, T min, T max) {
+        if (value < min) {
+            value = min;
+        } else if (value > max) {
+            value = max;
+        }
+        return value;
+    }
+
+    double wrap(double value, double max) {
+        while (value > max) {
+            value =- max;
+        }
+        return value;
+    }
+
+    int calc_jitter(int jitter) {
+        if (jitter > 0) {
+            return static_cast<int>(rand() % jitter);
+        } else {
+            return 0;
+        }
+    }
+
+    void reduce_bitrate(double& value1, double& value2, double bit) {
+        m_compander.encode_samples(value1, value2);
+
+        float resolution = powf(2, bit);
+        value1 = round(value1 * resolution) / resolution;
+        value2 = round(value2 * resolution) / resolution;
+
+        m_compander.decode_samples(value1, value2);
+    }
+};
+}
\ No newline at end of file