From e39a923b23cd1d71c7aca18a671639b8af383e09 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Fri, 24 Jun 2022 03:26:00 -0500
Subject: [PATCH] C64: fix per-channel osc for 6581

---
 src/engine/platform/c64.cpp           | 7 ++++---
 src/engine/platform/sound/c64/sid.cc  | 7 +++++++
 src/engine/platform/sound/c64/sid.h   | 1 +
 src/engine/platform/sound/c64/voice.h | 7 +++++++
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/engine/platform/c64.cpp b/src/engine/platform/c64.cpp
index 3372c8203..a55b53906 100644
--- a/src/engine/platform/c64.cpp
+++ b/src/engine/platform/c64.cpp
@@ -109,14 +109,15 @@ const char* DivPlatformC64::getEffectName(unsigned char effect) {
 }
 
 void DivPlatformC64::acquire(short* bufL, short* bufR, size_t start, size_t len) {
+  int dcOff=sid.get_dc(0);
   for (size_t i=start; i<start+len; i++) {
     sid.clock();
     bufL[i]=sid.output();
     if (++writeOscBuf>=8) {
       writeOscBuf=0;
-      oscBuf[0]->data[oscBuf[0]->needle++]=sid.last_chan_out[0]>>5;
-      oscBuf[1]->data[oscBuf[1]->needle++]=sid.last_chan_out[1]>>5;
-      oscBuf[2]->data[oscBuf[2]->needle++]=sid.last_chan_out[2]>>5;
+      oscBuf[0]->data[oscBuf[0]->needle++]=(sid.last_chan_out[0]-dcOff)>>5;
+      oscBuf[1]->data[oscBuf[1]->needle++]=(sid.last_chan_out[1]-dcOff)>>5;
+      oscBuf[2]->data[oscBuf[2]->needle++]=(sid.last_chan_out[2]-dcOff)>>5;
     }
   }
 }
diff --git a/src/engine/platform/sound/c64/sid.cc b/src/engine/platform/sound/c64/sid.cc
index d6ebbb449..aaed90a5f 100644
--- a/src/engine/platform/sound/c64/sid.cc
+++ b/src/engine/platform/sound/c64/sid.cc
@@ -60,6 +60,13 @@ SID::~SID()
   delete[] fir;
 }
 
+// ----------------------------------------------------------------------------
+// Get DC offset of channel.
+// ----------------------------------------------------------------------------
+sound_sample SID::get_dc(int ch) {
+  return voice[ch].getDC();
+}
+
 // ----------------------------------------------------------------------------
 // Mute/unmute channel.
 // ----------------------------------------------------------------------------
diff --git a/src/engine/platform/sound/c64/sid.h b/src/engine/platform/sound/c64/sid.h
index f6b392713..e8b0d5c6d 100644
--- a/src/engine/platform/sound/c64/sid.h
+++ b/src/engine/platform/sound/c64/sid.h
@@ -34,6 +34,7 @@ public:
 
   sound_sample last_chan_out[3];
 
+  sound_sample get_dc(int ch);
   void set_is_muted(int ch, bool val);
   void set_chip_model(chip_model model);
   void enable_filter(bool enable);
diff --git a/src/engine/platform/sound/c64/voice.h b/src/engine/platform/sound/c64/voice.h
index d248f32ae..85b4fedec 100644
--- a/src/engine/platform/sound/c64/voice.h
+++ b/src/engine/platform/sound/c64/voice.h
@@ -38,6 +38,7 @@ public:
   // Amplitude modulated waveform output.
   // Range [-2048*255, 2047*255].
   RESID_INLINE sound_sample output();
+  RESID_INLINE sound_sample getDC();
 
 protected:
   WaveformGenerator wave;
@@ -72,6 +73,12 @@ sound_sample Voice::output()
   return (wave.output() - wave_zero)*envelope.output() + voice_DC;
 }
 
+RESID_INLINE
+sound_sample Voice::getDC()
+{
+  return voice_DC;
+}
+
 #endif // RESID_INLINING || defined(__VOICE_CC__)
 
 #endif // not __VOICE_H__