SDL: x11: Avoid excess keymap reconstruction

From 3d42412650119a8e13a016e289e5860c034dde19 Mon Sep 17 00:00:00 2001
From: Frank Praznik <[EMAIL REDACTED]>
Date: Sun, 23 Jun 2024 17:52:21 -0400
Subject: [PATCH] x11: Avoid excess keymap reconstruction

KeymapNotify events happen on focus events, as well as when the key group changes. Query the current group and don't rebuild the keymap if it hasn't changed.
---
 src/video/x11/SDL_x11events.c   | 15 ++++++++++++++-
 src/video/x11/SDL_x11keyboard.c |  5 ++---
 src/video/x11/SDL_x11video.h    |  1 +
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/video/x11/SDL_x11events.c b/src/video/x11/SDL_x11events.c
index 043db8de53a34..1eef65fe5a13b 100644
--- a/src/video/x11/SDL_x11events.c
+++ b/src/video/x11/SDL_x11events.c
@@ -1131,7 +1131,20 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
             printf("window %p: KeymapNotify!\n", data);
 #endif
             if (SDL_GetKeyboardFocus() != NULL) {
-                X11_UpdateKeymap(_this, SDL_TRUE);
+#ifdef SDL_VIDEO_DRIVER_X11_HAS_XKBLOOKUPKEYSYM
+                if (videodata->xkb) {
+                    XkbStateRec state;
+                    X11_XkbGetUpdatedMap(videodata->display, XkbAllClientInfoMask, videodata->xkb);
+
+                    if (X11_XkbGetState(videodata->display, XkbUseCoreKbd, &state) == Success) {
+                        unsigned int group = state.group;
+                        if (group != videodata->xkb_group) {
+                            /* Only rebuild the keymap if the layout has changed. */
+                            X11_UpdateKeymap(_this, SDL_TRUE);
+                        }
+                    }
+                }
+#endif
                 X11_ReconcileKeyboardState(_this);
             }
         } else if (xevent->type == MappingNotify) {
diff --git a/src/video/x11/SDL_x11keyboard.c b/src/video/x11/SDL_x11keyboard.c
index 543c36e4a866b..9a5d25c9a9832 100644
--- a/src/video/x11/SDL_x11keyboard.c
+++ b/src/video/x11/SDL_x11keyboard.c
@@ -347,7 +347,6 @@ void X11_UpdateKeymap(SDL_VideoDevice *_this, SDL_bool send_event)
     int i;
     SDL_Scancode scancode;
     SDL_Keymap *keymap;
-    unsigned char group = 0;
 
     keymap = SDL_CreateKeymap();
 
@@ -357,7 +356,7 @@ void X11_UpdateKeymap(SDL_VideoDevice *_this, SDL_bool send_event)
         X11_XkbGetUpdatedMap(data->display, XkbAllClientInfoMask, data->xkb);
 
         if (X11_XkbGetState(data->display, XkbUseCoreKbd, &state) == Success) {
-            group = state.group;
+            data->xkb_group = state.group;
         }
     }
 #endif
@@ -372,7 +371,7 @@ void X11_UpdateKeymap(SDL_VideoDevice *_this, SDL_bool send_event)
                 continue;
             }
 
-            KeySym keysym = X11_KeyCodeToSym(_this, i, group, keymod_masks[m].xkb_mask);
+            KeySym keysym = X11_KeyCodeToSym(_this, i, data->xkb_group, keymod_masks[m].xkb_mask);
 
             /* Note: The default SDL scancode table sets this to right alt instead of AltGr/Mode, so handle it separately. */
             if (keysym != XK_ISO_Level3_Shift) {
diff --git a/src/video/x11/SDL_x11video.h b/src/video/x11/SDL_x11video.h
index 80b5c47997923..f8e567c777cc2 100644
--- a/src/video/x11/SDL_x11video.h
+++ b/src/video/x11/SDL_x11video.h
@@ -125,6 +125,7 @@ struct SDL_VideoData
     XkbDescPtr xkb;
 #endif
     int xkb_event;
+    unsigned int xkb_group;
 
     KeyCode filter_code;
     Time filter_time;