From bdce1c464a85e08777862bdac04fcc7062159e76 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 21 Apr 2020 00:09:42 -0400
Subject: [PATCH] Takes a shot at key-level scaling. Testing to come.

---
 Components/OPL2/Implementation/Operator.cpp | 51 ++++++++++++++++++++-
 Components/OPL2/Implementation/Operator.hpp |  2 +-
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/Components/OPL2/Implementation/Operator.cpp b/Components/OPL2/Implementation/Operator.cpp
index d75aca14d..53c693dcf 100644
--- a/Components/OPL2/Implementation/Operator.cpp
+++ b/Components/OPL2/Implementation/Operator.cpp
@@ -27,7 +27,7 @@ void Operator::set_sustain_release(uint8_t value) {
 }
 
 void Operator::set_scaling_output(uint8_t value) {
-	level_key_scaling_ = value >> 6;
+	key_level_scaling_ = value >> 6;
 	attenuation_ = value & 0x3f;
 }
 
@@ -174,6 +174,55 @@ void Operator::update(OperatorState &state, bool key_on, int channel_period, int
 		state.time_in_phase_ = 0;
 	}
 
+	// Calculate key-level scaling. Table is as per p14 of the YM3812 application manual,
+	// converted into a fixed-point scheme. Compare with https://www.smspower.org/Development/RE12
+	// and apologies for the highly ad hoc indentation.
+	constexpr int key_level_scales[4][8][16] = {
+#define _ 0
+		{
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
+		},
+		{
+			{_,	 _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _},
+			{_,  _,  _,  _,  _,  _,  _,  _,  _,  1,  1,  2,  2,  3,  3,  4},
+			{_,  _,  _,  _,  _,  1,  2,  3,  4,  5,  5,  6,  6,  7,  7,  8},
+			{_,  _,  _,  2,  4,  5,  6,  7,  8,  9,  9, 10, 10, 11, 11, 12},
+			{_,	 _,  4,  6,  8,  9, 10, 11, 12, 13, 13, 14, 14, 15, 15, 16},
+			{_,	 4,  8, 10, 12, 13, 14, 15, 16, 17, 17, 18, 18, 19, 19, 20},
+			{_,	 8, 12, 14, 16, 17, 18, 19, 20, 21, 21, 22, 22, 23, 23, 24},
+			{_,	12, 16, 18, 20, 21, 22, 23, 24, 25, 25, 26, 26, 27, 27, 28},
+		},
+		{
+			{_,	 _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _},
+			{_,  _,  _,  _,  _,  _,  _,  _,  _,  2,  3,  4,  5,  6,  7,  8},
+			{_,  _,  _,  _,  _,  3,  5,  7,  8, 10, 11, 12, 13, 14, 15, 16},
+			{_,  _,  _,  5,  8, 11, 13, 15, 16, 18, 19, 20, 21, 22, 23, 24},
+			{_,	 _,  8, 13, 16, 19, 21, 23, 24, 26, 27, 28, 29, 30, 31, 32},
+			{_,	 8, 16, 21, 24, 27, 29, 31, 32, 34, 35, 36, 37, 38, 39, 40},
+			{_,	16, 24, 29, 32, 35, 37, 39, 40, 42, 43, 44, 45, 46, 47, 48},
+			{_,	24, 32, 37, 40, 43, 45, 47, 48, 50, 51, 52, 53, 54, 55, 56},
+		},
+		{
+			{_,	  _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _},
+			{_,   _,   _,   _,   _,   _,   _,   _,   _,   4,   6,   8,  10,  12,  14,  16},
+			{_,   _,   _,   _,   _,   6,  10,  14,  16,  20,  22,  24,  26,  28,  30,  32},
+			{_,   _,   _,  10,  16,  22,  26,  30,  32,  36,  38,  40,  42,  44,  46,  48},
+			{_,	  _,  16,  26,  32,  38,  42,  46,  48,  52,  54,  56,  58,  60,  62,  64},
+			{_,	 16,  32,  42,  48,  54,  58,  62,  64,  68,  70,  72,  74,  76,  78,  80},
+			{_,	 32,  48,  58,  64,  70,  74,  78,  80,  84,  86,  88,  90,  92,  94,  96},
+			{_,	 48,  64,  74,  80,  86,  90,  94,  96, 100, 102, 104, 106, 108, 110, 112},
+		},
+#undef _
+	};
+	state.attenuation.log += key_level_scales[key_level_scaling_][channel_octave][channel_period >> 6] << 7;
+
 	// Combine the ADSR attenuation and overall channel attenuation.
 	if(overrides) {
 		// Overrides here represent per-channel volume on an OPLL. The bits are defined to represent
diff --git a/Components/OPL2/Implementation/Operator.hpp b/Components/OPL2/Implementation/Operator.hpp
index 0ec73a40e..22cb4f8c2 100644
--- a/Components/OPL2/Implementation/Operator.hpp
+++ b/Components/OPL2/Implementation/Operator.hpp
@@ -114,7 +114,7 @@ class Operator {
 		bool key_scaling_rate_ = false;
 
 		/// Selects attenuation that is applied as a function of interval. Cf. p14.
-		int level_key_scaling_ = 0;
+		int key_level_scaling_ = 0;
 
 		/// Sets the ADSR rates. These all provide the top four bits of a six-bit number;
 		/// the bottom two bits... are 'RL'?