From 08dd693fa0f8a125637cd8bd523e55ecd400eee7 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Sun, 27 Mar 2022 00:02:17 -0500
Subject: [PATCH] Amiga: add AM/PM effects

---
 papers/doc/7-systems/amiga.md |  6 +++++-
 src/engine/dispatch.h         |  2 ++
 src/engine/platform/amiga.cpp | 21 +++++++++++++++++++++
 src/engine/platform/amiga.h   |  4 +++-
 src/engine/playback.cpp       |  8 ++++++++
 5 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/papers/doc/7-systems/amiga.md b/papers/doc/7-systems/amiga.md
index 713300c29..97c1151f6 100644
--- a/papers/doc/7-systems/amiga.md
+++ b/papers/doc/7-systems/amiga.md
@@ -6,4 +6,8 @@ in this very computer music trackers were born...
 
 # effects
 
-- `10xx`: toggle low-pass filter. `0` turns it off and `1` turns it on.
\ No newline at end of file
+- `10xx`: toggle low-pass filter. `0` turns it off and `1` turns it on.
+- `11xx`: toggle amplitude modulation with the next channel.
+  - does not work on the last channel.
+- `12xx`: toggle period (frequency) modulation with the next channel.
+  - does not work on the last channel.
\ No newline at end of file
diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index b535df52d..15f1cf0d5 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -107,6 +107,8 @@ enum DivDispatchCmds {
   DIV_CMD_SAA_ENVELOPE,
 
   DIV_CMD_AMIGA_FILTER,
+  DIV_CMD_AMIGA_AM,
+  DIV_CMD_AMIGA_PM,
 
   DIV_CMD_LYNX_LFSR_LOAD,
   
diff --git a/src/engine/platform/amiga.cpp b/src/engine/platform/amiga.cpp
index a58de52f5..b0f25f728 100644
--- a/src/engine/platform/amiga.cpp
+++ b/src/engine/platform/amiga.cpp
@@ -17,6 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#define _USE_MATH_DEFINES
 #include "amiga.h"
 #include "../engine.h"
 #include <math.h>
@@ -68,6 +69,12 @@ const char* DivPlatformAmiga::getEffectName(unsigned char effect) {
     case 0x10:
       return "10xx: Toggle filter (0 disables; 1 enables)";
       break;
+    case 0x11:
+      return "11xx: Toggle AM with next channel";
+      break;
+    case 0x12:
+      return "12xx: Toggle period modulation with next channel";
+      break;
   }
   return NULL;
 }
@@ -84,6 +91,14 @@ void DivPlatformAmiga::acquire(short* bufL, short* bufR, size_t start, size_t le
           DivSample* s=parent->getSample(chan[i].sample);
           if (s->samples>0) {
             chan[i].audDat=s->data8[chan[i].audPos++];
+            if (i<3 && chan[i].useV) {
+              chan[i+1].outVol=(unsigned char)chan[i].audDat^0x80;
+              if (chan[i+1].outVol>64) chan[i+1].outVol=64;
+            }
+            if (i<3 && chan[i].useP) {
+              chan[i+1].freq=(unsigned char)chan[i].audDat^0x80;
+              if (chan[i+1].freq>AMIGA_DIVIDER) chan[i+1].freq=AMIGA_DIVIDER;
+            }
             if (chan[i].audPos>=s->samples || chan[i].audPos>=131071) {
               if (s->loopStart>=0 && s->loopStart<(int)s->samples) {
                 chan[i].audPos=s->loopStart;
@@ -319,6 +334,12 @@ int DivPlatformAmiga::dispatch(DivCommand c) {
       filterOn=c.value;
       filtConst=filterOn?filtConstOn:filtConstOff;
       break;
+    case DIV_CMD_AMIGA_AM:
+      chan[c.chan].useV=c.value;
+      break;
+    case DIV_CMD_AMIGA_PM:
+      chan[c.chan].useP=c.value;
+      break;
     case DIV_CMD_GET_VOLMAX:
       return 64;
       break;
diff --git a/src/engine/platform/amiga.h b/src/engine/platform/amiga.h
index d73918e96..b5f13701d 100644
--- a/src/engine/platform/amiga.h
+++ b/src/engine/platform/amiga.h
@@ -36,7 +36,7 @@ class DivPlatformAmiga: public DivDispatch {
     unsigned char ins;
     int busClock;
     int note;
-    bool active, insChanged, freqChanged, keyOn, keyOff, inPorta, useWave, setPos;
+    bool active, insChanged, freqChanged, keyOn, keyOff, inPorta, useWave, setPos, useV, useP;
     signed char vol, outVol;
     DivMacroInt std;
     Channel():
@@ -61,6 +61,8 @@ class DivPlatformAmiga: public DivDispatch {
       inPorta(false),
       useWave(false),
       setPos(false),
+      useV(false),
+      useP(false),
       vol(64),
       outVol(64) {}
   };
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 7d089e609..4ab6a517c 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -115,6 +115,8 @@ const char* cmdName[DIV_CMD_MAX]={
   "SAA_ENVELOPE",
 
   "AMIGA_FILTER",
+  "AMIGA_AM",
+  "AMIGA_PM",
   
   "LYNX_LFSR_LOAD",
 
@@ -656,6 +658,12 @@ bool DivEngine::perSystemPostEffect(int ch, unsigned char effect, unsigned char
         case 0x10: // toggle filter
           dispatchCmd(DivCommand(DIV_CMD_AMIGA_FILTER,ch,effectVal));
           break;
+        case 0x11: // toggle AM
+          dispatchCmd(DivCommand(DIV_CMD_AMIGA_AM,ch,effectVal));
+          break;
+        case 0x12: // toggle PM
+          dispatchCmd(DivCommand(DIV_CMD_AMIGA_PM,ch,effectVal));
+          break;
         default:
           return false;
       }