GTK Focus issue when used with SDL

[btzy]

This is the same as mlabbe/nativefiledialog#79, where the file dialog goes under an existing SDL window. It does not happen in the tests where we are launching the dialog directly from the terminal.

Tested on Ubuntu 20.04.

[btzy]

Test case (modified from mlabbe/nativefiledialog#79):

main.c:

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

#include <SDL.h>

#include <nfd.h>

int main()
{
    SDL_Init(SDL_INIT_VIDEO);
    
    NFD_Init();

    SDL_Window *window = SDL_CreateWindow("nativefiledialog issue 79", SDL_WINDOWPOS_CENTERED,
            SDL_WINDOWPOS_CENTERED, 800, 480, SDL_WINDOW_SHOWN);

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

    bool running = true;
    while (running) {
        SDL_Event e;
        while (SDL_PollEvent(&e)) {
            if (e.type == SDL_QUIT) {
                running = false;
                break;
            }
            if (e.type == SDL_MOUSEBUTTONDOWN) {
                nfdchar_t *filename;
                nfdresult_t res = NFD_OpenDialog(&filename, NULL, 0, NULL);
                if (res == NFD_OKAY) {
                    printf("Got filename: %s\n", filename);
                    free(filename);
                }
            }
        }
    }

    SDL_DestroyWindow(window);
    
    NFD_Quit();
    
    SDL_Quit();

    return 0;
}

CMakeLists.txt:

cmake_minimum_required(VERSION 3.2)
project(MyProgram)


set (CMAKE_CXX_STANDARD 17)


add_executable(MyProgram main.c)

find_package(PkgConfig REQUIRED)
pkg_check_modules(SDL2 REQUIRED sdl2)
target_include_directories(MyProgram PRIVATE ${SDL2_INCLUDE_DIRS})
target_link_libraries(MyProgram PRIVATE ${SDL2_LIBRARIES})

add_subdirectory(${PROJECT_SOURCE_DIR}/../nativefiledialog-extended ${PROJECT_SOURCE_DIR}/../nativefiledialog-extended/build)
target_link_libraries(MyProgram PRIVATE nfd)