Fixed bug 3458 - x11: reset deadkeys in StartTextInput/StopTextInput

Eric Wasylishen

The patch makes StartTextInput/StopTextInput call Xutf8ResetIC ( https://www.x.org/releases/X11R7.5/doc/man/man3/XmbResetIC.3.html ) on the XIC of all SDL windows.

This fixes my use case in Quakespasm (Ubuntu 16.04, system keyboard layout set to German. Type the '^' dead key, which opens Quakespasm's developer console and calls SDL_StartTextInput, then press 'e'. I expect the dead key to be ignored.)

Also, here is a patch for sdl2's "checkkeys" for testing this: https://bugzilla-attachments.libsdl.org/attachment.cgi?id=2451
diff --git a/src/video/x11/SDL_x11keyboard.c b/src/video/x11/SDL_x11keyboard.c
index e7e1a56..b888bff 100644
--- a/src/video/x11/SDL_x11keyboard.c
+++ b/src/video/x11/SDL_x11keyboard.c
@@ -427,15 +427,38 @@
 #endif
 }
 
+static void
+X11_ResetXIM(_THIS)
+{
+#ifdef X_HAVE_UTF8_STRING
+    SDL_VideoData *videodata = (SDL_VideoData *) _this->driverdata;
+    int i;
+
+    if (videodata && videodata->windowlist) {
+        for (i = 0; i < videodata->numwindows; ++i) {
+            SDL_WindowData *data = videodata->windowlist[i];
+            if (data && data->ic) {
+                /* Clear any partially entered dead keys */
+                char *contents = X11_Xutf8ResetIC(data->ic);
+                if (contents) {
+                    X11_XFree(contents);
+                }
+            }
+        }
+    }
+#endif
+}
+
 void
 X11_StartTextInput(_THIS)
 {
-
+    X11_ResetXIM(_this);
 }
 
 void
 X11_StopTextInput(_THIS)
 {
+    X11_ResetXIM(_this);
 #ifdef SDL_USE_IME
     SDL_IME_Reset();
 #endif
diff --git a/src/video/x11/SDL_x11sym.h b/src/video/x11/SDL_x11sym.h
index c9840d8..7290412 100644
--- a/src/video/x11/SDL_x11sym.h
+++ b/src/video/x11/SDL_x11sym.h
@@ -201,6 +201,7 @@
 SDL_X11_SYM(void,Xutf8DrawString,(Display *a, Drawable b, XFontSet c, GC d, int e, int f, _Xconst char *g, int h),(a,b,c,d,e,f,g,h),)
 SDL_X11_SYM(int,Xutf8TextExtents,(XFontSet a, _Xconst char*	b, int c, XRectangle* d, XRectangle* e),(a,b,c,d,e),return)
 SDL_X11_SYM(char*,XSetLocaleModifiers,(const char *a),(a),return)
+SDL_X11_SYM(char*,Xutf8ResetIC,(XIC a),(a),return)
 #endif
 
 #ifndef NO_SHARED_MEMORY