From 0c5a6d976074f3ad2d3378f680d8467a973bb135 Mon Sep 17 00:00:00 2001
From: cam900 <dbtlrchl@naver.com>
Date: Sat, 13 May 2023 18:54:05 +0900
Subject: [PATCH] Just resample rather than reset

---
 extern/opl/MODIFIED.md      | 2 +-
 extern/opl/opl3.c           | 5 +++++
 extern/opl/opl3.h           | 1 +
 src/engine/platform/opl.cpp | 7 ++++++-
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/extern/opl/MODIFIED.md b/extern/opl/MODIFIED.md
index 78341ad4..d5a39e9f 100644
--- a/extern/opl/MODIFIED.md
+++ b/extern/opl/MODIFIED.md
@@ -1,4 +1,4 @@
 # modification disclaimer
 
-this is a modified version of Nuked-OPL3 which implements channel muting in the core.
+this is a modified version of Nuked-OPL3 which implements channel muting in the core, and resampling function.
 see [this issue](https://github.com/tildearrow/furnace/issues/414) for more information.
diff --git a/extern/opl/opl3.c b/extern/opl/opl3.c
index 3358f033..5acdca25 100644
--- a/extern/opl/opl3.c
+++ b/extern/opl/opl3.c
@@ -1362,6 +1362,11 @@ void OPL3_Reset(opl3_chip *chip, uint32_t samplerate)
 #endif
 }
 
+void OPL3_Resample(opl3_chip *chip, uint32_t samplerate)
+{
+    chip->rateratio = (samplerate << RSM_FRAC) / 49716;
+}
+
 void OPL3_WriteReg(opl3_chip *chip, uint16_t reg, uint8_t v)
 {
     uint8_t high = (reg >> 8) & 0x01;
diff --git a/extern/opl/opl3.h b/extern/opl/opl3.h
index 8d515323..1e88a801 100644
--- a/extern/opl/opl3.h
+++ b/extern/opl/opl3.h
@@ -158,6 +158,7 @@ struct _opl3_chip {
 void OPL3_Generate(opl3_chip *chip, int16_t *buf);
 void OPL3_GenerateResampled(opl3_chip *chip, int16_t *buf);
 void OPL3_Reset(opl3_chip *chip, uint32_t samplerate);
+void OPL3_Resample(opl3_chip *chip, uint32_t samplerate);
 void OPL3_WriteReg(opl3_chip *chip, uint16_t reg, uint8_t v);
 void OPL3_WriteRegBuffered(opl3_chip *chip, uint16_t reg, uint8_t v);
 void OPL3_GenerateStream(opl3_chip *chip, int16_t *sndptr, uint32_t numsamples);
diff --git a/src/engine/platform/opl.cpp b/src/engine/platform/opl.cpp
index 3ce997e5..863663a5 100644
--- a/src/engine/platform/opl.cpp
+++ b/src/engine/platform/opl.cpp
@@ -1866,7 +1866,12 @@ void DivPlatformOPL::setFlags(const DivConfig& flags) {
           totalOutputs=4;
           break;
       }
-      reset();
+      if (downsample) {
+        const unsigned int downsampledRate=(unsigned int)((double)rate*49716.0/(double)chipRateBase);
+        OPL3_Resample(&fm,downsampledRate);
+      } else {
+        OPL3_Resample(&fm,rate);
+      }
       break;
     case 4:
       switch (flags.getInt("clockSel",0)) {