Added FM synth

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_synth/lib/src/opl2_emulator.dart

@@ -2,44 +2,39 @@ import 'dart:math' as math;
 
 enum EnvelopeState { off, attack, decay, sustain, release }
 
-class Opl2Channel {
-  int fNum = 0;
-  int block = 0;
-  bool keyOn = false;
-
+class Opl2Operator {
   double phase = 0.0;
   double phaseIncrement = 0.0;
 
-  // ADSR Parameters (0.0 to 1.0 scales or rates per sample)
+  // ADSR
   double attackRate = 0.01;
   double decayRate = 0.005;
   double sustainLevel = 0.5;
   double releaseRate = 0.005;
-
-  // Current Envelope State
   EnvelopeState envState = EnvelopeState.off;
   double envVolume = 0.0;
 
-  void updateFrequency() {
-    double realFreq = (fNum * math.pow(2, block)) * (49716.0 / 1048576.0);
-    phaseIncrement = (realFreq * 2 * math.pi) / Opl2Emulator.sampleRate;
+  // FM specific parameters
+  double multiplier = 1.0;
+  double volume =
+      1.0; // Acts as volume for Carrier, but "Modulation Strength" for Modulator
+
+  void updateFrequency(double baseFreq) {
+    phaseIncrement =
+        (baseFreq * multiplier * 2 * math.pi) / Opl2Emulator.sampleRate;
   }
 
   void triggerOn() {
-    if (!keyOn) {
-      keyOn = true;
-      phase = 0.0;
-      envState = EnvelopeState.attack;
-    }
+    phase = 0.0;
+    envState = EnvelopeState.attack;
   }
 
   void triggerOff() {
-    keyOn = false;
     envState = EnvelopeState.release;
   }
 
-  double getSample() {
-    // Process the ADSR state machine
+  // phaseOffset is where the Modulator feeds into the Carrier
+  double getSample(double phaseOffset) {
     switch (envState) {
       case EnvelopeState.attack:
         envVolume += attackRate;
@@ -56,7 +51,6 @@ class Opl2Channel {
         }
         break;
       case EnvelopeState.sustain:
-        // Holds steady at the sustain level
         envVolume = sustainLevel;
         break;
       case EnvelopeState.release:
@@ -68,19 +62,48 @@ class Opl2Channel {
         break;
       case EnvelopeState.off:
         envVolume = 0.0;
-        return 0.0; // Early exit for silence
+        return 0.0;
     }
 
-    // Generate the sine wave
-    double out = math.sin(phase);
+    // Add the Modulator's output to our current phase!
+    double out = math.sin(phase + phaseOffset);
 
     phase += phaseIncrement;
-    if (phase >= 2 * math.pi) {
-      phase -= 2 * math.pi;
+    if (phase >= 2 * math.pi) phase -= 2 * math.pi;
+
+    return out * envVolume * volume;
+  }
+}
+
+class Opl2Channel {
+  Opl2Operator modulator = Opl2Operator();
+  Opl2Operator carrier = Opl2Operator();
+
+  int fNum = 0;
+  int block = 0;
+  bool keyOn = false;
+
+  void updateFrequency() {
+    double baseFreq = (fNum * math.pow(2, block)) * (49716.0 / 1048576.0);
+    modulator.updateFrequency(baseFreq);
+    carrier.updateFrequency(baseFreq);
+  }
+
+  double getSample() {
+    if (!keyOn &&
+        carrier.envState == EnvelopeState.off &&
+        modulator.envState == EnvelopeState.off) {
+      return 0.0;
     }
 
-    // Multiply the raw sine wave by our current envelope volume
-    return (out * envVolume) * 0.1;
+    // 1. Get the modulator's output (it takes no phase offset itself)
+    // We multiply it by an arbitrary index (e.g. 2.0) to give it enough strength to warp the carrier
+    double modOutput = modulator.getSample(0.0) * 2.0;
+
+    // 2. Feed the modulator's output directly into the carrier's phase!
+    double carOutput = carrier.getSample(modOutput);
+
+    return carOutput * 0.1; // Master channel volume reduction
   }
 }
 
@@ -89,59 +112,68 @@ class Opl2Emulator {
 
   final List<Opl2Channel> channels = List.generate(9, (_) => Opl2Channel());
 
-  // Real OPL2 chips use 2 operators (oscillators) per channel.
-  // This maps the IMF register offsets to find the "Carrier" operator for our 9 channels.
-  static const List<int> _carrierOffsets = [
-    0x03,
-    0x04,
-    0x05,
-    0x0B,
-    0x0C,
-    0x0D,
-    0x13,
-    0x14,
-    0x15,
+  // The OPL2 maps 18 operators to 9 channels in a very fragmented memory layout.
+  // This helper array maps a register offset (0x00 to 0x15) to a specific channel and operator type.
+  static const List<int> _operatorMap = [
+    0, 1, 2, 0, 1, 2, // Offsets 0x00-0x05 (Ch 0-2 Modulators, then Carriers)
+    -1, -1, // Offsets 0x06-0x07 (Unused)
+    3, 4, 5, 3, 4, 5, // Offsets 0x08-0x0D (Ch 3-5 Modulators, then Carriers)
+    -1, -1, // Offsets 0x0E-0x0F (Unused)
+    6, 7, 8, 6, 7, 8, // Offsets 0x10-0x15 (Ch 6-8 Modulators, then Carriers)
   ];
 
-  int _getChannelIndexForOperator(int regOffset) {
-    return _carrierOffsets.indexOf(regOffset);
+  Opl2Operator? _getOperator(int offset) {
+    if (offset < 0 ||
+        offset >= _operatorMap.length ||
+        _operatorMap[offset] == -1) {
+      return null;
+    }
+    int channelIdx = _operatorMap[offset];
+
+    // In our map, if the offset relative to the block is < 3, it's a Modulator.
+    // Otherwise, it's a Carrier.
+    bool isCarrier = (offset % 8) >= 3;
+
+    return isCarrier
+        ? channels[channelIdx].carrier
+        : channels[channelIdx].modulator;
   }
 
   void writeRegister(int reg, int data) {
-    // --- 0x60 - 0x75: Attack (Upper 4 bits) & Decay (Lower 4 bits) ---
-    if (reg >= 0x60 && reg <= 0x75) {
-      int offset = reg - 0x60;
-      int channelIdx = _getChannelIndexForOperator(offset);
-
-      if (channelIdx != -1) {
-        // If it's a carrier operator
-        int attack = (data & 0xF0) >> 4;
-        int decay = data & 0x0F;
-
-        // Map the 0-15 hardware values to our simple rate scales
-        // (15 is fastest, 0 is slowest/infinite)
-        channels[channelIdx].attackRate = attack == 0
-            ? 0.0
-            : (attack / 15.0) * 0.05;
-        channels[channelIdx].decayRate = decay == 0
-            ? 0.0
-            : (decay / 15.0) * 0.005;
+    // --- 0x20 - 0x35: Multiplier ---
+    if (reg >= 0x20 && reg <= 0x35) {
+      var op = _getOperator(reg - 0x20);
+      if (op != null) {
+        int mult = data & 0x0F;
+        op.multiplier = mult == 0 ? 0.5 : mult.toDouble();
       }
     }
-    // --- 0x80 - 0x95: Sustain (Upper 4 bits) & Release (Lower 4 bits) ---
+    // --- 0x40 - 0x55: Total Level (Volume) ---
+    else if (reg >= 0x40 && reg <= 0x55) {
+      var op = _getOperator(reg - 0x40);
+      if (op != null) {
+        int level = data & 0x3F; // 0 is loudest, 63 is quietest
+        op.volume = 1.0 - (level / 63.0);
+      }
+    }
+    // --- 0x60 - 0x75: Attack & Decay ---
+    else if (reg >= 0x60 && reg <= 0x75) {
+      var op = _getOperator(reg - 0x60);
+      if (op != null) {
+        int attack = (data & 0xF0) >> 4;
+        int decay = data & 0x0F;
+        op.attackRate = attack == 0 ? 0.0 : (attack / 15.0) * 0.05;
+        op.decayRate = decay == 0 ? 0.0 : (decay / 15.0) * 0.005;
+      }
+    }
+    // --- 0x80 - 0x95: Sustain & Release ---
     else if (reg >= 0x80 && reg <= 0x95) {
-      int offset = reg - 0x80;
-      int channelIdx = _getChannelIndexForOperator(offset);
-
-      if (channelIdx != -1) {
+      var op = _getOperator(reg - 0x80);
+      if (op != null) {
         int sustain = (data & 0xF0) >> 4;
         int release = data & 0x0F;
-
-        // OPL2 sustain is inverted (0 is loudest, 15 is quietest)
-        channels[channelIdx].sustainLevel = 1.0 - (sustain / 15.0);
-        channels[channelIdx].releaseRate = release == 0
-            ? 0.0
-            : (release / 15.0) * 0.005;
+        op.sustainLevel = 1.0 - (sustain / 15.0);
+        op.releaseRate = release == 0 ? 0.0 : (release / 15.0) * 0.005;
       }
     }
     // --- 0xA0 - 0xA8: F-Number (Lower 8 bits) ---
@@ -160,11 +192,14 @@ class Opl2Emulator {
       channel.fNum = (channel.fNum & 0xFF) | ((data & 0x03) << 8);
       channel.updateFrequency();
 
-      // Trigger the ADSR envelope appropriately
       if (newKeyOn && !channel.keyOn) {
-        channel.triggerOn();
+        channel.keyOn = true;
+        channel.modulator.triggerOn();
+        channel.carrier.triggerOn();
       } else if (!newKeyOn && channel.keyOn) {
-        channel.triggerOff();
+        channel.keyOn = false;
+        channel.modulator.triggerOff();
+        channel.carrier.triggerOff();
       }
     }
   }