SDL3 Wayland: `SDL_EVENT_KEYMAP_CHANGED` spam when typing in Russian

[raiguard]

When typing in Russian on GNOME Wayland, SDL absolutely pummels the app with SDL_EVENT_KEYMAP_CHANGED events:

encoded.mp4

On Sway, it doesn't send any text input events whatsoever when in Russian, using the following config:

input type:keyboard xkb_layout us,ru
bindsym $mod+Backspace input type:keyboard xkb_switch_layout next

Interestingly, you can also notice in the video that when I switched from Russian to Japanese, SDL continued to produce text input events in Russian.

Demo code

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>
#include <stdio.h>

static SDL_Window* window;
static SDL_Renderer* renderer;
static char inputbuf[4096];

int main() {
    SDL_zero(inputbuf);

    SDL_SetHint(SDL_HINT_EVENT_LOGGING, "1");

    SDL_CreateWindowAndRenderer("sdl_testapp", 1280, 720, SDL_WINDOW_HIGH_PIXEL_DENSITY | SDL_WINDOW_RESIZABLE, &window, &renderer);

    SDL_SetRenderVSync(renderer, 1);

    SDL_StartTextInput(window);

    bool quit = false;
    SDL_Event event;
    while (!quit) {
        while (!quit && SDL_PollEvent(&event)) {
            if (event.type == SDL_EVENT_QUIT) {
                quit = true;
            } else if (event.type == SDL_EVENT_KEY_UP && event.key.scancode == SDL_SCANCODE_RETURN) {
                SDL_StopTextInput(window);
            } else if (event.type == SDL_EVENT_KEY_DOWN && event.key.scancode == SDL_SCANCODE_BACKSPACE) {
                if (SDL_strlen(inputbuf) > 0)
                    inputbuf[SDL_strlen(inputbuf) - 1] = 0;
            } else if (event.type == SDL_EVENT_TEXT_INPUT)
                SDL_strlcat(inputbuf, event.text.text, sizeof(inputbuf));
            else if (event.type == SDL_EVENT_MOUSE_BUTTON_UP) {
                SDL_StartTextInput(window);
            }
        }

        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_RenderClear(renderer);

        int w, h;
        SDL_GetWindowSizeInPixels(window, &w, &h);

        SDL_SetWindowTitle(window, inputbuf);

        char* buf = NULL;
        SDL_asprintf(&buf, "Dimensions: %ix%i\nText input active: %b\nScreen keyboard shown: %b",
                     w, h, SDL_TextInputActive(window), SDL_ScreenKeyboardShown(window));
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderDebugText(renderer, 10, 10, buf);
        SDL_free(buf);

        SDL_RenderPresent(renderer);
    }
}

[Kontrabant]

The Wayland back end checks the bound keymap on key events and switches it as necessary, as some compositors support multiple, simultaneously active keyboards with independent layouts. The bug is in the code that checks the currently bound keymap when using keyboards with non-latin characters if certain keycode options hints are set (the problematic hint values are also the defaults). Should be a simple fix, which I will take care of tomorrow.

Interestingly, you can also notice in the video that when I switched from Russian to Japanese, SDL continued to produce text input events in Russian.

This definitely isn't an SDL bug, as I can replicate it in the very text box I'm typing this in, as well as my IDE and various text editors.

[raiguard]

I am pretty sure that the "failure" to switch to japanese was because I forgot to actually trigger the IME input after selecting it. I will test this theory tomorrow.

[raiguard]

I can confirm that the russian -> japanese thing happens in librewolf as well, so you are right, it's not an SDL bug. 👍
Thanks for the quick fix!