From 5641e06a19f30e2fa8a4a6593e2a83fd3c3797d8 Mon Sep 17 00:00:00 2001
From: bicarus-dev <202771338+bicarus-dev@users.noreply.github.com>
Date: Mon, 10 Nov 2025 11:35:46 -0800
Subject: [PATCH] iidx: fix kana input broken in subscreen when system language
 is not Japanese (#421)

## Link to GitHub Issue, if one exists
user-reported

## Description of change
When the system non-Unicode language is not set to Japanese, TDJ
subscreen katakana keyboard was broken (weird behavior with characters
not erasing, ending with corrupt characters, etc)

To fix this, add a hook for `IsDBCSLeadByte`. `IsDBCSLeadByte` assumes
system ACP (which may not be SHIFT_JIS). Instead, redirect bm2dx.dll to
use `IsDBCSLeadByteEx` instead with SHIFT_JIS explicitly specified as a
parameter.

Presumably the game was using IsDBCSLeadByte to manage the keyboard
typing logic.... which is weird because SDVX doesn't do the same.

## Testing
Tested iidx 31 and tried to do searches.
---
 src/spice2x/hooks/lang.cpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/spice2x/hooks/lang.cpp b/src/spice2x/hooks/lang.cpp
index a247822..b10d36d 100644
--- a/src/spice2x/hooks/lang.cpp
+++ b/src/spice2x/hooks/lang.cpp
@@ -8,6 +8,7 @@
 #include <ntstatus.h>
 
 #include "avs/game.h"
+#include "games/iidx/iidx.h"
 #include "util/detour.h"
 #include "util/logging.h"
 #include "util/utils.h"
@@ -22,6 +23,7 @@ static decltype(GetLocaleInfoEx) *GetLocaleInfoEx_orig = nullptr;
 
 #ifdef SPICE64
 static decltype(GetSystemDefaultLCID) *GetSystemDefaultLCID_orig = nullptr;
+static decltype(IsDBCSLeadByte) *IsDBCSLeadByte_orig = nullptr;
 #endif
 
 static NTSTATUS NTAPI RtlMultiByteToUnicodeN_hook(
@@ -162,6 +164,17 @@ static int WINAPI GetLocaleInfoEx_hook (
     return GetLocaleInfoEx_orig(lpLocaleName, LCType, lpLCData, cchData);
 }
 
+#ifdef SPICE64
+
+static BOOL WINAPI IsDBCSLeadByte_hook (
+    BYTE TestChar
+    )
+{
+    return IsDBCSLeadByteEx(CODEPAGE_SHIFT_JIS, TestChar);
+}
+
+#endif
+
 void hooks::lang::early_init() {
     log_info("hooks::lang", "early initialization");
 
@@ -189,6 +202,19 @@ void hooks::lang::early_init() {
             GetLocaleInfoEx_hook,
             &GetLocaleInfoEx_orig);
     }
+
+#ifdef SPICE64
+    // for TDJ subscreen search keyboard
+    if (avs::game::is_model("LDJ") && games::iidx::TDJ_MODE) {
+        log_info("hooks::lang", "hooking IsDBCSLeadByte");
+        detour::trampoline_try(
+            "kernel32.dll",
+            "IsDBCSLeadByte",
+            IsDBCSLeadByte_hook,
+            &IsDBCSLeadByte_orig);
+    }
+#endif
+
 }
 
 void hooks::lang::init() {