Checking basic information about a connection

Once we have opened a connection to an X server, we should check some basic information about it: what screens it has, what is the size (width and height) of the screen, how many colors it supports (black and white ? grey scale ?, 256 colors ? more ?), and so on. We get such information from the xcb_screen_t structure:

typedef struct {
    xcb_window_t   root;
    xcb_colormap_t default_colormap;
    uint32_t       white_pixel;
    uint32_t       black_pixel;
    uint32_t       current_input_masks;
    uint16_t       width_in_pixels;
    uint16_t       height_in_pixels;
    uint16_t       width_in_millimeters;
    uint16_t       height_in_millimeters;
    uint16_t       min_installed_maps;
    uint16_t       max_installed_maps;
    xcb_visualid_t root_visual;
    uint8_t        backing_stores;
    uint8_t        save_unders;
    uint8_t        root_depth;
    uint8_t        allowed_depths_len;
} xcb_screen_t;

typedef struct {
    xcb_window_t   root;
    xcb_colormap_t default_colormap;
    uint32_t       white_pixel;
    uint32_t       black_pixel;
    uint32_t       current_input_masks;
    uint16_t       width_in_pixels;
    uint16_t       height_in_pixels;
    uint16_t       width_in_millimeters;
    uint16_t       height_in_millimeters;
    uint16_t       min_installed_maps;
    uint16_t       max_installed_maps;
    xcb_visualid_t root_visual;
    uint8_t        backing_stores;
    uint8_t        save_unders;
    uint8_t        root_depth;
    uint8_t        allowed_depths_len;
} xcb_screen_t;

We could retrieve the first screen of the connection by using the following function:

xcb_screen_iterator_t xcb_setup_roots_iterator (xcb_setup_t *R);

xcb_screen_iterator_t xcb_setup_roots_iterator (xcb_setup_t *R);

Here is a small program that shows how to use this function:

#include <stdio.h>

#include <xcb/xcb.h>

int
main ()
{
  xcb_connection_t     *c;
  xcb_screen_t         *screen;
  int                   screen_nbr;
  xcb_screen_iterator_t iter;

  /* Open the connection to the X server. Use the DISPLAY environment variable */
  c = xcb_connect (NULL, &screen_nbr);

  /* Get the screen #screen_nbr */
  iter = xcb_setup_roots_iterator (xcb_get_setup (c));
  for (; iter.rem; --screen_nbr, xcb_screen_next (&iter))
    if (screen_nbr == 0) {
      screen = iter.data;
      break;
    }

  printf ("\n");
  printf ("Informations of screen %ld:\n", screen->root);
  printf ("  width.........: %d\n", screen->width_in_pixels);
  printf ("  height........: %d\n", screen->height_in_pixels);
  printf ("  white pixel...: %ld\n", screen->white_pixel);
  printf ("  black pixel...: %ld\n", screen->black_pixel);
  printf ("\n");

  return 0;
}

#include <stdio.h>

#include <xcb/xcb.h>

int
main ()
{
  xcb_connection_t     *c;
  xcb_screen_t         *screen;
  int                   screen_nbr;
  xcb_screen_iterator_t iter;

  /* Open the connection to the X server. Use the DISPLAY environment variable */
  c = xcb_connect (NULL, &screen_nbr);

  /* Get the screen #screen_nbr */
  iter = xcb_setup_roots_iterator (xcb_get_setup (c));
  for (; iter.rem; --screen_nbr, xcb_screen_next (&iter))
    if (screen_nbr == 0) {
      screen = iter.data;
      break;
    }

  printf ("\n");
  printf ("Informations of screen %ld:\n", screen->root);
  printf ("  width.........: %d\n", screen->width_in_pixels);
  printf ("  height........: %d\n", screen->height_in_pixels);
  printf ("  white pixel...: %ld\n", screen->white_pixel);
  printf ("  black pixel...: %ld\n", screen->black_pixel);
  printf ("\n");

  return 0;
}