From 1e6e595484cc32aba4297546c042d4f4eb376822 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Sat, 1 Oct 2016 11:54:02 -0700
Subject: [PATCH] Fixed bug 3332 - Win32: reset deadkeys in
 StartTextInput/StopTextInput

Eric Wasylishen

The bug here is that a dead keys pressed before calling SDL_StartTextInput() carries over into future text input, so the next key pressed will have the deadkey applied to it.

This in undesirable, imho, and doesn't occur on OS X (haven't check Linux or elsewhere). It's causing a problem for Quakespasm on German keyboard layouts, where we use the ^ deadkey to toggle the console (which enables/disables text input), and ^ characters are showing up in the TEXTINPUT events.
---
 src/video/windows/SDL_windowskeyboard.c | 50 ++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/video/windows/SDL_windowskeyboard.c b/src/video/windows/SDL_windowskeyboard.c
index d3e16c8bfc98a..de72ad7958309 100644
--- a/src/video/windows/SDL_windowskeyboard.c
+++ b/src/video/windows/SDL_windowskeyboard.c
@@ -157,11 +157,51 @@ WIN_QuitKeyboard(_THIS)
 #endif
 }
 
+void
+WIN_ResetDeadKeys()
+{
+    /*
+    if a deadkey has been typed, but not the next character (which the deadkey might modify), 
+    this tries to undo the effect pressing the deadkey.
+    see: http://archives.miloush.net/michkap/archive/2006/09/10/748775.html
+    */
+
+    BYTE keyboardState[256];
+    WCHAR buffer[16];
+    int keycode, scancode, result, i;
+
+    GetKeyboardState(keyboardState);
+
+    keycode = VK_SPACE;
+    scancode = MapVirtualKey(keycode, MAPVK_VK_TO_VSC);
+    if (scancode == 0)
+    {
+        /* the keyboard doesn't have this key */
+        return;
+    }
+
+    for (i = 0; i < 5; i++)
+    {
+        result = ToUnicode(keycode, scancode, keyboardState, (LPWSTR)buffer, 16, 0);
+        if (result > 0)
+        {
+            /* success */
+            return;
+        }
+    }
+}
+
 void
 WIN_StartTextInput(_THIS)
 {
 #ifndef SDL_DISABLE_WINDOWS_IME
-    SDL_Window *window = SDL_GetKeyboardFocus();
+    SDL_Window *window;
+#endif
+
+    WIN_ResetDeadKeys();
+
+#ifndef SDL_DISABLE_WINDOWS_IME
+    window = SDL_GetKeyboardFocus();
     if (window) {
         HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
         SDL_VideoData *videodata = (SDL_VideoData *)_this->driverdata;
@@ -176,7 +216,13 @@ void
 WIN_StopTextInput(_THIS)
 {
 #ifndef SDL_DISABLE_WINDOWS_IME
-    SDL_Window *window = SDL_GetKeyboardFocus();
+    SDL_Window *window;
+#endif
+
+    WIN_ResetDeadKeys();
+
+#ifndef SDL_DISABLE_WINDOWS_IME
+    window = SDL_GetKeyboardFocus();
     if (window) {
         HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
         SDL_VideoData *videodata = (SDL_VideoData *)_this->driverdata;