From ff9f336be3c3e182a14152c844aad2d9b669aed8 Mon Sep 17 00:00:00 2001
From: Gwilym Inzani <email@gwilym.dev>
Date: Wed, 15 Nov 2023 15:29:55 +0000
Subject: [PATCH] Do pitch bend correctly

---
 tracker/agb-midi-core/src/lib.rs | 12 +++---------
 tracker/agb-tracker/src/lib.rs   |  4 +++-
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/tracker/agb-midi-core/src/lib.rs b/tracker/agb-midi-core/src/lib.rs
index 0852a660..e9f03446 100644
--- a/tracker/agb-midi-core/src/lib.rs
+++ b/tracker/agb-midi-core/src/lib.rs
@@ -273,16 +273,10 @@ pub fn parse_midi(midi_info: &MidiInfo) -> TokenStream {
                     }
                     midly::MidiMessage::Aftertouch { .. } => {}
                     midly::MidiMessage::PitchBend { bend } => {
-                        // bend is between 0 and 8192 where 0 = -2 semitones and 8193 is +2 semitones (I think)
-                        let amount = (bend.0.as_int() as f64 - (8192.0 / 2.0)) / (8192.0 / 2.0);
+                        // bend is between 0 and 16383 where 0 = -2 semitones and 16384 is +2 semitones (I think)
+                        let amount = (bend.0.as_int() as f64 - (16384.0 / 2.0)) / (16384.0 / 2.0);
 
-                        // amount is now between -1 and 1
-                        let two_semitones_multiplier = 493.88 / 440.0; // B4 / A4
-                        let amount = if amount < 0.0 {
-                            1.0 / two_semitones_multiplier * (-amount)
-                        } else {
-                            two_semitones_multiplier * amount
-                        };
+                        let amount = 2.0f64.powf((amount * 2.0) / 12.0);
 
                         pattern.push(PatternSlot {
                             speed: 0.into(),
diff --git a/tracker/agb-tracker/src/lib.rs b/tracker/agb-tracker/src/lib.rs
index 85254b90..8735df45 100644
--- a/tracker/agb-tracker/src/lib.rs
+++ b/tracker/agb-tracker/src/lib.rs
@@ -112,6 +112,7 @@ pub struct Tracker {
 #[derive(Default)]
 struct TrackerChannel {
     channel_id: Option<ChannelId>,
+    original_speed: Num<u32, 16>,
     base_speed: Num<u32, 16>,
     volume: Num<i32, 8>,
 }
@@ -328,6 +329,7 @@ impl TrackerChannel {
         {
             if speed != 0.into() {
                 self.base_speed = speed.change_base();
+                self.original_speed = self.base_speed;
             }
 
             channel.playback(self.base_speed.change_base());
@@ -430,7 +432,7 @@ impl TrackerChannel {
                 }
                 PatternEffect::PitchBend(amount) => {
                     if tick == 0 {
-                        self.base_speed *= amount.change_base();
+                        self.base_speed = self.original_speed * amount.change_base();
                         channel.playback(self.base_speed.change_base());
                     }
                 }