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X11 Backend with multiple windows

This example shows how to create multiple X11 windows.

// SPDX-License-Identifier: GPL-2.1-or-later
/*
 * Copyright (C) 2009-2013 Cyril Hrubis <metan@ucw.cz>
 */

 /*

   Simple backend example.

  */

#include <stdio.h>
#include <gfxprim.h>

static void redraw(struct gp_pixmap *pixmap)
{
        gp_pixel white_pixel, black_pixel;

        black_pixel = gp_rgb_to_pixmap_pixel(0x00, 0x00, 0x00, pixmap);
        white_pixel = gp_rgb_to_pixmap_pixel(0xff, 0xff, 0xff, pixmap);

        gp_fill(pixmap, black_pixel);
        gp_line(pixmap, 0, 0, pixmap->w - 1, pixmap->h - 1, white_pixel);
        gp_line(pixmap, 0, pixmap->h - 1, pixmap->w - 1, 0, white_pixel);
}

static int ev_loop(struct gp_backend *backend, const char *name)
{
        gp_event *ev;

        if (backend == NULL)
                return 0;

        while ((ev = gp_backend_get_event(backend))) {

                printf("-------------------------- %s\n", name);

                gp_event_dump(ev);

                switch (ev->type) {
                case GP_EV_KEY:
                        switch (ev->val) {
                        case GP_KEY_ESC:
                        case GP_KEY_Q:
                                gp_backend_exit(backend);
                                return 1;
                        break;
                        }
                break;
                case GP_EV_SYS:
                        switch (ev->code) {
                        case GP_EV_SYS_RESIZE:
                                gp_backend_resize_ack(backend);
                                redraw(backend->pixmap);
                                gp_backend_flip(backend);
                        break;
                        case GP_EV_SYS_QUIT:
                                gp_backend_exit(backend);
                                return 1;
                        break;
                        }
                break;
                }

                printf("-----------------------------\n");
        }

        return 0;
}

int main(void)
{
        gp_backend *win_1, *win_2;

        win_1 = gp_x11_init(NULL, 0, 0, 300, 300, "win 1", 0);
        win_2 = gp_x11_init(NULL, 0, 0, 300, 300, "win 2", 0);

        if (win_1 == NULL || win_2 == NULL) {
                gp_backend_exit(win_1);
                gp_backend_exit(win_2);
                return 1;
        }

        /* Update the backend screen */
        redraw(win_1->pixmap);
        redraw(win_2->pixmap);

        gp_backend_flip(win_1);
        gp_backend_flip(win_2);

        for (;;) {
                /*
                 * Wait for backend event.
                 *
                 * Either window is fine as they share connection.
                 */
                gp_backend *b = win_1 ? win_1 : win_2;

                if (b == NULL)
                        return 0;

                gp_backend_wait(b);

                if (ev_loop(win_1, "win 1"))
                        win_1 = NULL;

                if (ev_loop(win_2, "win 2"))
                        win_2 = NULL;
        }

        gp_backend_exit(win_1);
        gp_backend_exit(win_2);

        return 0;
}