X11: Handle WM_STATE transitions to detect Withdrawn/Iconic states

[Jipok]

Description

When running SDL3 applications on tiling window managers like i3, moving a window to an invisible workspace does not trigger SDL_WINDOW_MINIMIZED or SDL_WINDOW_HIDDEN. Consequently, the application continues rendering at full speed (VSync dependent), consuming unnecessary GPU/CPU resources even when not visible.

When a workspace is hidden, i3(and possible other tiling WMs) unmaps the container and sets the client window state to WithdrawnState (via the WM_STATE atom). Previously, the SDL3 X11 backend ignored changes to WM_STATE during PropertyNotify events, failing to detect this transition.

I provide a test program to log window flags and FPS:

Details

// gcc sdl3_test.c -o sdl3_test -lSDL3
// Code written by LLM
#include <SDL3/SDL.h>
#include <stdio.h>

void LogFlags(SDL_Window *window) {
    Uint32 flags = SDL_GetWindowFlags(window);
    printf("[STATUS] Flags: ");
    if (flags & SDL_WINDOW_FULLSCREEN) printf("FULLSCREEN ");
    if (flags & SDL_WINDOW_OCCLUDED) printf("OCCLUDED (Перекрыто) ");
    if (flags & SDL_WINDOW_HIDDEN) printf("HIDDEN (Скрыто) ");
    if (flags & SDL_WINDOW_MINIMIZED) printf("MINIMIZED ");
    if (flags & SDL_WINDOW_MAXIMIZED) printf("MAXIMIZED ");
    if (flags & SDL_WINDOW_INPUT_FOCUS) printf("INPUT_FOCUS ");
    if (flags & SDL_WINDOW_MOUSE_FOCUS) printf("MOUSE_FOCUS ");
    printf("\n");
}

int main(int argc, char *argv[]) {
    if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS)) {
        fprintf(stderr, "SDL init error: %s\n", SDL_GetError());
        return 1;
    }

    SDL_Window *window = SDL_CreateWindow("SDL3 i3 Test", 800, 600, SDL_WINDOW_RESIZABLE);
    if (!window) return 1;

    int running = 1;
    Uint64 last_tick = SDL_GetTicks();
    int frames = 0;

    LogFlags(window);

    while (running) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            switch (event.type) {
                case SDL_EVENT_QUIT: running = 0; break;
                
                case SDL_EVENT_WINDOW_SHOWN:     printf("[EVENT] WINDOW_SHOWN\n"); break;
                case SDL_EVENT_WINDOW_HIDDEN:    printf("[EVENT] WINDOW_HIDDEN\n"); break;
                case SDL_EVENT_WINDOW_EXPOSED:   printf("[EVENT] WINDOW_EXPOSED\n"); break;
                case SDL_EVENT_WINDOW_MINIMIZED: printf("[EVENT] WINDOW_MINIMIZED (!!!)\n"); break;
                case SDL_EVENT_WINDOW_RESTORED:  printf("[EVENT] WINDOW_RESTORED\n"); break;
                case SDL_EVENT_WINDOW_OCCLUDED:  printf("[EVENT] WINDOW_OCCLUDED\n"); break;
                
                case SDL_EVENT_WINDOW_FOCUS_GAINED: printf("[EVENT] FOCUS_GAINED\n"); break;
                case SDL_EVENT_WINDOW_FOCUS_LOST:   printf("[EVENT] FOCUS_LOST\n"); break;

                // Noise
                case SDL_EVENT_MOUSE_MOTION: 
                case SDL_EVENT_WINDOW_MOVED:
                    break;

                default:
                    // printf("[EVENT] Unknown: 0x%x\n", event.type);
                    break;
            }
        }

        // Work emulation
        frames++;
        Uint8 r = (frames % 255);
        SDL_Surface *surface = SDL_GetWindowSurface(window);
        const SDL_PixelFormatDetails *details = SDL_GetPixelFormatDetails(surface->format);
        Uint32 rectColor = SDL_MapRGB(details, NULL, r, 0, 0);
        SDL_FillSurfaceRect(surface, NULL, rectColor);
        SDL_UpdateWindowSurface(window);

        // Ping every second
        Uint64 current_tick = SDL_GetTicks();
        if (current_tick - last_tick >= 1000) {
            printf("--- PING: FPS: %d ---\n", frames);
            LogFlags(window); 
            frames = 0;
            last_tick = current_tick;
        }
    }

    SDL_Quit();
    return 0;
}

Before fix:

[STATUS] Flags: INPUT_FOCUS
[EVENT] WINDOW_EXPOSED
[EVENT] WINDOW_SHOWN
[EVENT] FOCUS_GAINED
--- PING: FPS: 586 ---
[STATUS] Flags: INPUT_FOCUS
--- PING: FPS: 582 ---
[STATUS] Flags: INPUT_FOCUS
--- PING: FPS: 604 ---                  
[STATUS] Flags: INPUT_FOCUS
[EVENT] FOCUS_LOST
--- PING: FPS: 758 ---                <-- Low because visible
[STATUS] Flags: MAXIMIZED
--- PING: FPS: 1640 ---               <-- Spikes because invisible, but app thinks it's active
[STATUS] Flags: MAXIMIZED
--- PING: FPS: 1632 ---
[STATUS] Flags: MAXIMIZED
--- PING: FPS: 1623 ---

After fix:

[STATUS] Flags: INPUT_FOCUS
[EVENT] FOCUS_LOST
[EVENT] WINDOW_MINIMIZED (!!!)
--- PING: FPS: 1306 ---
[STATUS] Flags: MINIMIZED

Existing Issue(s)

I'm sure I've seen somewhere that people are complaining about games on i3wm hogging the CPU/GPU in the background, but I can't find it now.

[Kontrabant]

Can you squash the commits into one for merging?