From 649a1419a8465eae5c65c38da3705f00fa4a8123 Mon Sep 17 00:00:00 2001
From: Hans Kokx <hans.d.kokx@gmail.com>
Date: Sun, 15 Mar 2026 13:01:54 +0100
Subject: [PATCH] Added drums, snares, etc. OPL2 emulator is now feature
 complete.

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>
---
 .../wolf_3d_synth/lib/src/opl2_emulator.dart  | 100 +++++++++++++++++-
 1 file changed, 98 insertions(+), 2 deletions(-)

diff --git a/packages/wolf_3d_synth/lib/src/opl2_emulator.dart b/packages/wolf_3d_synth/lib/src/opl2_emulator.dart
index 19ec22c..63069bb 100644
--- a/packages/wolf_3d_synth/lib/src/opl2_emulator.dart
+++ b/packages/wolf_3d_synth/lib/src/opl2_emulator.dart
@@ -147,9 +147,31 @@ class Opl2Channel {
   }
 }
 
+class Opl2Noise {
+  int _seed = 0xFFFF;
+
+  // Simple 16-bit LFSR to match OPL2 noise characteristics
+  double next() {
+    int bit = ((_seed >> 0) ^ (_seed >> 2) ^ (_seed >> 3) ^ (_seed >> 5)) & 1;
+    _seed = (_seed >> 1) | (bit << 15);
+    return ((_seed & 1) == 1) ? 1.0 : -1.0;
+  }
+}
+
 class Opl2Emulator {
   static const int sampleRate = 44100;
 
+  bool rhythmMode = false;
+
+  // Key states for the 5 drums
+  bool bassDrumKey = false;
+  bool snareDrumKey = false;
+  bool tomTomKey = false;
+  bool topCymbalKey = false;
+  bool hiHatKey = false;
+
+  final Opl2Noise _noise = Opl2Noise();
+
   final List<Opl2Channel> channels = List.generate(9, (_) => Opl2Channel());
 
   // The master lock for waveforms
@@ -276,14 +298,88 @@ class Opl2Emulator {
           op.waveform = data & 0x03;
         }
       }
+    } else if (reg == 0xBD) {
+      rhythmMode = (data & 0x20) != 0; // Bit 5: Rhythm Enable
+
+      // Bits 0-4: Key-On for individual drums
+      bassDrumKey = (data & 0x10) != 0;
+      snareDrumKey = (data & 0x08) != 0;
+      tomTomKey = (data & 0x04) != 0;
+      topCymbalKey = (data & 0x02) != 0;
+      hiHatKey = (data & 0x01) != 0;
     }
   }
 
   double generateSample() {
     double mixedOutput = 0.0;
-    for (var channel in channels) {
-      mixedOutput += channel.getSample();
+
+    // Channels 0-5 always act as normal melodic FM channels
+    for (int i = 0; i < 6; i++) {
+      mixedOutput += channels[i].getSample();
     }
+
+    if (!rhythmMode) {
+      // Standard mode: play channels 6, 7, and 8 normally
+      for (int i = 6; i < 9; i++) {
+        mixedOutput += channels[i].getSample();
+      }
+    } else {
+      // RHYTHM MODE: The last 3 channels are re-routed
+      mixedOutput += _generateBassDrum();
+      mixedOutput += _generateSnareAndHiHat();
+      mixedOutput += _generateTomAndCymbal();
+    }
+
     return mixedOutput.clamp(-1.0, 1.0);
   }
+
+  // Example of Bass Drum logic (Channel 6)
+  double _generateBassDrum() {
+    if (!bassDrumKey) return 0.0;
+    // Bass drum uses standard FM (Mod -> Car) but usually with very low frequency
+    return channels[6].getSample();
+  }
+
+  double _generateSnareAndHiHat() {
+    double snareOut = 0.0;
+    double hiHatOut = 0.0;
+
+    // Snare uses Channel 7 Modulator
+    if (snareDrumKey) {
+      // The Snare is a mix of a periodic tone and white noise
+      double noise = _noise.next();
+      snareOut = channels[7].modulator.getSample(0.0) * noise;
+    }
+
+    // Hi-Hat uses Channel 7 Carrier
+    if (hiHatKey) {
+      // Hi-Hats are almost pure high-frequency noise
+      hiHatOut =
+          _noise.next() *
+          channels[7].carrier.envVolume *
+          channels[7].carrier.volume;
+    }
+
+    return (snareOut + hiHatOut) * 0.1;
+  }
+
+  double _generateTomAndCymbal() {
+    double tomOut = 0.0;
+    double cymbalOut = 0.0;
+
+    // Tom-tom uses Channel 8 Modulator
+    if (tomTomKey) {
+      // Toms are basically just a melodic sine wave with a fast decay
+      tomOut = channels[8].modulator.getSample(0.0);
+    }
+
+    // Top Cymbal uses Channel 8 Carrier
+    if (topCymbalKey) {
+      // Cymbals use the carrier but are usually phase-modulated by noise
+      double noise = _noise.next();
+      cymbalOut = channels[8].carrier.getSample(noise * 2.0);
+    }
+
+    return (tomOut + cymbalOut) * 0.1;
+  }
 }