// This example program creates an EGL surface from a GBM surface.
    //
    // If the macro EGL_KHR_platform_gbm is defined, then the program
    // creates the surfaces using the methods defined in this specification.
    // Otherwise, it uses the methods defined by the EGL 1.4 specification.
    //
    // Compile with `cc -std=c99 example.c -lgbm -lEGL`.

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

    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>

    #include <EGL/egl.h>
    #include <gbm.h>

    struct my_display {
        struct gbm_device *gbm;
        EGLDisplay egl;
    };

    struct my_config {
        struct my_display dpy;
        EGLConfig egl;
    };

    struct my_window {
        struct my_config config;
        struct gbm_surface *gbm;
        EGLSurface egl;
    };

    static void
    check_extensions(void)
    {
    #ifdef EGL_KHR_platform_gbm
        const char *client_extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);

        if (!client_extensions) {
            // No client extensions string available
		printf("no client");
            abort();
        }
        if (!strstr(client_extensions, "EGL_KHR_platform_gbm")) {
		printf("no client ext");
            abort();
        }
    #endif
    }

    static struct my_display
    get_display(void)
    {
        struct my_display dpy;

        int fd = open("/dev/dri/card0", O_RDWR | FD_CLOEXEC);
        if (fd < 0) {
		printf("fb < 0 \n");
            abort();
        }

	printf("gbm create device \n");
        dpy.gbm = gbm_create_device(fd);
        if (!dpy.gbm) {
		printf("!dpy.gbm \n");
            abort();
        }


	printf("getting platform display \n");
    #ifdef EGL_KHR_platform_gbm
        dpy.egl = eglGetPlatformDisplay(EGL_PLATFORM_GBM_KHR, dpy.gbm, NULL);
    #else
        dpy.egl = eglGetDisplay(dpy.gbm);
    #endif

        if (dpy.egl == EGL_NO_DISPLAY) {
		printf("EGL_NO_DISPLAY \n");
            abort();
        }

        EGLint major, minor;
        if (!eglInitialize(dpy.egl, &major, &minor)) {
		printf("egl init fail \n");
            abort();
        }

        return dpy;
    }

    static struct my_config
    get_config(struct my_display dpy)
    {
        struct my_config config = {
            .dpy = dpy,
        };

        EGLint egl_config_attribs[] = {
            EGL_BUFFER_SIZE,        32,
            EGL_DEPTH_SIZE,         EGL_DONT_CARE,
            EGL_STENCIL_SIZE,       EGL_DONT_CARE,
            EGL_RENDERABLE_TYPE,    EGL_OPENGL_ES2_BIT,
            EGL_SURFACE_TYPE,       EGL_WINDOW_BIT,
            EGL_NONE,
        };

        EGLint num_configs;
        if (!eglGetConfigs(dpy.egl, NULL, 0, &num_configs)) {
            abort();
        }

        EGLConfig *configs = malloc(num_configs * sizeof(EGLConfig));
        if (!eglChooseConfig(dpy.egl, egl_config_attribs,
                             configs, num_configs, &num_configs)) {
            abort();
        }
        if (num_configs == 0) {
            abort();
        }

        // Find a config whose native visual ID is the desired GBM format.
        for (int i = 0; i < num_configs; ++i) {
            EGLint gbm_format;

            if (!eglGetConfigAttrib(dpy.egl, configs[i],
                                    EGL_NATIVE_VISUAL_ID, &gbm_format)) {
                abort();
            }

            if (gbm_format == GBM_FORMAT_XRGB8888) {
                config.egl = configs[i];
                free(configs);
                return config;
            }
        }

        // Failed to find a config with matching GBM format.
        abort();
    }

    static struct my_window
    get_window(struct my_config config)
    {
        struct my_window window = {
            .config = config,
        };

        window.gbm = gbm_surface_create(config.dpy.gbm,
                                        256, 256,
                                        GBM_FORMAT_XRGB8888,
                                        GBM_BO_USE_RENDERING);
        if (!window.gbm) {
            abort();
        }

    #ifdef EGL_KHR_platform_gbm
        window.egl = eglCreatePlatformWindowSurface(config.dpy.egl,
                                                    config.egl,
                                                    window.gbm,
                                                    NULL);
    #else
        window.egl = eglCreateWindowSurface(config.dpy.egl,
                                            config.egl,
                                            window.gbm,
                                            NULL);
    #endif

        if (window.egl == EGL_NO_SURFACE) {
            abort();
        }

        return window;
    }

    int
    main(void)
    {
	printf("checking extensions \n");
        check_extensions();

	printf("getting display \n");
        struct my_display dpy = get_display();
	printf("get config \n");
        struct my_config config = get_config(dpy);
	printf("getting window \n");
        struct my_window window = get_window(config);

        return 0;
    }