From 5794d9c9926c35df0afa2ac7f901d234dfe668f6 Mon Sep 17 00:00:00 2001
From: alyosha-tas <alexei.f.k@gmail.com>
Date: Sun, 14 Nov 2021 11:12:01 -0500
Subject: [PATCH] SMS: Fix ys (JPN) byemulating VRAm masking bit

---
 src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs |  5 ++++-
 .../Consoles/Sega/SMS/VDP.Mode4.cs                   |  7 ++++++-
 src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.cs | 12 ++++++++++--
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs
index e3574087d0..0749f66865 100644
--- a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs
+++ b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs
@@ -86,6 +86,9 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 				MemoryCallbacks = MemoryCallbacks,
 				OnExecFetch = OnExecMemory
 			};
+			
+			// set this before turning off GG system for GG_in_SMS games
+			bool sms_reg_compat = !IsGameGear && (_region == SmsSyncSettings.Regions.Japan);
 
 			if (game["GG_in_SMS"])
 			{
@@ -99,7 +102,7 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 
 			SystemId = game.System;
 
-			Vdp = new VDP(this, Cpu, IsGameGear ? VdpMode.GameGear : VdpMode.SMS, Region);
+			Vdp = new VDP(this, Cpu, IsGameGear ? VdpMode.GameGear : VdpMode.SMS, Region, sms_reg_compat);
 			ser.Register<IVideoProvider>(Vdp);
 			PSG = new SN76489sms();
 			YM2413 = new YM2413();
diff --git a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.Mode4.cs b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.Mode4.cs
index bb6b8c63e3..3688c1b1b9 100644
--- a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.Mode4.cs
+++ b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.Mode4.cs
@@ -47,7 +47,12 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 				}
 
 				byte PaletteBase = 0;
-				int tileInfo = VRAM[mapBase + ((yTile * 32) + xTile) * 2] | (VRAM[mapBase + (((yTile * 32) + xTile) * 2) + 1] << 8);
+
+				int VRAM_addr = mapBase + ((yTile * 32) + xTile) * 2;
+				if (JPN_Compat) { VRAM_addr &= NameTableMaskBit; }
+
+				int tileInfo = VRAM[VRAM_addr] | (VRAM[VRAM_addr + 1] << 8);
+
 				int tileNo = tileInfo & 0x01FF;
 				if ((tileInfo & 0x800) != 0)
 					PaletteBase = 16;
diff --git a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.cs b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.cs
index 102ed0d0c2..0de119f047 100644
--- a/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.cs
+++ b/src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/VDP.cs
@@ -1,6 +1,7 @@
 using BizHawk.Common;
 using BizHawk.Emulation.Common;
 using BizHawk.Emulation.Cores.Components.Z80A;
+using System;
 
 namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 {
@@ -71,6 +72,11 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 		private int TmsPatternNameTableBase;
 		private int TmsSpriteAttributeBase;
 
+		// older versions fo the SMS VDP have a masking bit in register two that effects mirroring.
+		// This is needed for Ys (JPN) in the status bar
+		private int NameTableMaskBit;
+		private bool JPN_Compat =false;
+
 		// preprocessed state assist stuff.
 		public int[] Palette = new int[32];
 		public byte[] PatternBuffer = new byte[0x8000];
@@ -81,7 +87,7 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 		private static readonly byte[] SMSPalXlatTable = { 0, 85, 170, 255 };
 		private static readonly byte[] GGPalXlatTable = { 0, 17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255 };
 
-		public VDP(SMS sms, Z80A cpu, VdpMode mode, DisplayType displayType)
+		public VDP(SMS sms, Z80A cpu, VdpMode mode, DisplayType displayType, bool region_compat)
 		{
 			Sms = sms;
 			Cpu = cpu;
@@ -89,7 +95,8 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 			if (mode == VdpMode.SMS) CRAM = new byte[32];
 			if (mode == VdpMode.GameGear) CRAM = new byte[64];
 			DisplayType = displayType;
-			NameTableBase = CalcNameTableBase();
+			if (mode == VdpMode.SMS) { JPN_Compat = region_compat; }
+			NameTableBase = CalcNameTableBase();	
 		}
 
 		public byte ReadData()
@@ -218,6 +225,7 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 
 		public int CalcNameTableBase()
 		{
+			if (JPN_Compat) { NameTableMaskBit = 0xFBFF + ((Registers[2] & 1) << 10); }
 			if (FrameHeight == 192)
 				return 1024 * (Registers[2] & 0x0E);
 			return (1024 * (Registers[2] & 0x0C)) + 0x0700;