From c484f737ad8a0c8e47b3bac3feab88e32eeff5cc Mon Sep 17 00:00:00 2001
From: Grant Shangreaux <grant@unabridgedsoftware.com>
Date: Sat, 30 Oct 2021 00:33:57 -0500
Subject: Add: phase based sine wave oscillator and comment GDscript

---
 klangfarb/main.gd      | 24 ++++++++++++++++++------
 klangfarbrs/src/lib.rs | 12 +++++++-----
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/klangfarb/main.gd b/klangfarb/main.gd
index 82f8ce9..fb29c8c 100644
--- a/klangfarb/main.gd
+++ b/klangfarb/main.gd
@@ -1,22 +1,34 @@
 extends AudioStreamPlayer
-var playback: AudioStreamPlayback = null
 
+# controllable frequency interface
+export(float, 20, 8000, 10) var freq = 440.0
+
+# load the GDNative script connected to the rust lib
 var SineWave = preload("res://SineWave.gdns")
+# make an instance of our one "class" in rust lib
 var wave = SineWave.new()
-var freq = 440.0
+
+# initialize the Godot stream we fill up with samples
+var playback: AudioStreamPlayback = null
 
 func _fill_buffer() -> void:
+	# get count of Frames (sample, sample) available in stream
 	var to_fill = playback.get_frames_available()
-	print(to_fill)
 	if to_fill > 0:
+		# ask Rust to generate N frames at freq
+		# Array<Vector2> gets pushed to the 
+		# playback stream buffer
 		playback.push_buffer(wave.frames(freq, to_fill)) 
 
 func _process(_delta):
-	_fill_buffer()
+		_fill_buffer()
 
 func _ready() -> void:
-	self.stream.mix_rate = freq * 256
-	wave.set_sample_rate(freq * 256)
+	# ensure Godot/Sine have the same sample rate
+	wave.set_sample_rate(self.stream.mix_rate)
+	# get our AudioStreamPlayback object
 	playback = self.get_stream_playback()
+	# prefill the stream's sample buffer (which feeds DAC)
 	_fill_buffer()
+	# start the audio
 	self.play()
diff --git a/klangfarbrs/src/lib.rs b/klangfarbrs/src/lib.rs
index 0628e34..64f3bda 100644
--- a/klangfarbrs/src/lib.rs
+++ b/klangfarbrs/src/lib.rs
@@ -6,13 +6,14 @@ use std::f32::consts::TAU;
 #[derive(NativeClass)]
 #[inherit(Node)]
 pub struct SineWave {
-    sample_rate: f32
+    sample_rate: f32,
+    phase: f32
 }
 
 #[methods]
 impl SineWave {
     fn new(_owner: &Node) -> Self {
-        SineWave { sample_rate: 44100.0 }
+        SineWave { sample_rate: 44100.0, phase: 0.0 }
     }
 
     #[export]
@@ -26,12 +27,13 @@ impl SineWave {
     }
 
     #[export]
-    pub fn frames(&self, _owner: &Node, frequency: f32, duration: i32) -> TypedArray<Vector2> {
+    pub fn frames(&mut self, _owner: &Node, frequency: f32, duration: i32) -> TypedArray<Vector2> {
         let mut frames = TypedArray::new();
 
-        for i in 0..duration as i32 {
-            let sample = (TAU * frequency * i as f32/self.sample_rate).sin();
+        for _i in 0..duration {
+            let sample = (TAU * self.phase).sin().clamp(-1.0, 1.0);
             frames.push(Vector2::new(sample, sample));
+            self.phase = (self.phase + (frequency / self.sample_rate)) % 1.0;
         }
 
         return frames
-- 
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