Xlib window which tells its own position and size

This program is very similar to A simple text window using Xlib, which creates an X window with some centred text. This program uses XTranslateCoordinates to print its own position in its own window, as well as its size.

The program also uses methods described in Responding to resize events with Xlib and Responding to window deletion messages from the window manager.

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <X11/Xlib.h>

/* The window which contains the text. */

struct {
    int width;
    int height;

    /* The strings containing the information. */

    char * coord_text;
    int coord_text_len;
    char * size_text;
    int size_text_len;

    /* X Windows related variables. */

    Display * display;
    int screen;
    Window root;
    Window window;
    GC gc;
    XFontStruct * font;
    unsigned long black_pixel;    
    unsigned long white_pixel;
}
text_box;

/* Connect to the display, set up the basic variables. */

static void x_connect ()
{
    text_box.display = XOpenDisplay (NULL);
    if (! text_box.display) {
        fprintf (stderr, "Could not open display.\n");
        exit (1);
    }
    text_box.screen = DefaultScreen (text_box.display);
    text_box.root = RootWindow (text_box.display, text_box.screen);
    text_box.black_pixel = BlackPixel (text_box.display, text_box.screen);
    text_box.white_pixel = WhitePixel (text_box.display, text_box.screen);
}

/* Create the window. */

static void create_window ()
{
    text_box.width = 300;
    text_box.height = 300;
    text_box.window = 
        XCreateSimpleWindow (text_box.display,
                             text_box.root,
                             1, /* x */
                             1, /* y */
                             text_box.width,
                             text_box.height,
                             0, /* border width */
                             text_box.black_pixel, /* border pixel */
                             text_box.white_pixel  /* background */);
    XSelectInput (text_box.display, text_box.window,
                  ExposureMask |

                  /* Add StructureNotifyMask to send us events
                     involving resizing of the window, etc. */

                  StructureNotifyMask);
    XMapWindow (text_box.display, text_box.window);
}

/* Set up the GC (Graphics Context). */

static void set_up_gc ()
{
    text_box.screen = DefaultScreen (text_box.display);
    text_box.gc = XCreateGC (text_box.display, text_box.window, 0, 0);
    XSetBackground (text_box.display, text_box.gc, text_box.white_pixel); 
    XSetForeground (text_box.display, text_box.gc, text_box.black_pixel); 
}

/* Set up the text font. */

static void set_up_font ()
{
    const char * fontname = "-*-helvetica-*-r-*-*-18-*-*-*-*-*-*-*";
    text_box.font = XLoadQueryFont (text_box.display, fontname);
    /* If the font could not be loaded, revert to the "fixed" font. */
    if (! text_box.font) {
        fprintf (stderr, "unable to load font %s: using fixed\n", fontname);
        text_box.font = XLoadQueryFont (text_box.display, "fixed");
    }
    XSetFont (text_box.display, text_box.gc, text_box.font->fid);
}

/* Get the current coordinates of the window. */

static void get_coordinates ()
{
    int x, y;
    Window child_return;

    XTranslateCoordinates (text_box.display, text_box.window, text_box.root,
                           0, 0, & x, & y, & child_return);
    if (text_box.coord_text) {
        free (text_box.coord_text);
    }
    if (text_box.size_text) {
        free (text_box.size_text);
    }
    text_box.coord_text_len =
        asprintf (& text_box.coord_text, "Coordinates are x:%d y:%d", x, y);
    text_box.size_text_len =
        asprintf (& text_box.size_text, "Sizes are width:%d height:%d",
                  text_box.width, text_box.height);
}

/* Put "text" at coordinates "x" and "y". */

static void put_text (int x, int y, const char * text, int text_len)
{
    XDrawString (text_box.display, text_box.window, text_box.gc,
                 x, y, text, text_len);
}

/* Draw the window. */

static void draw_screen ()
{
    int x;
    int y;
    int direction;
    int ascent;
    int descent;
    XCharStruct overall;

    get_coordinates ();

    XClearWindow (text_box.display, text_box.window);

    /* Text placement. */

    XTextExtents (text_box.font, text_box.coord_text, text_box.coord_text_len,
                  & direction, & ascent, & descent, & overall);
    x = (text_box.width - overall.width) / 2;
    y = text_box.height / 4 + ascent/2;
    put_text (x, y, text_box.coord_text, text_box.coord_text_len);
    XTextExtents (text_box.font, text_box.size_text, text_box.size_text_len,
                  & direction, & ascent, & descent, & overall);
    x = (text_box.width - overall.width) / 2;
    y = (3 * text_box.height) / 4 + ascent/2;
    put_text (x, y, text_box.size_text, text_box.size_text_len);
}

/* Loop over events. */

static void event_loop ()
{
    Atom wm_delete_window;
    wm_delete_window =
        XInternAtom (text_box.display, "WM_DELETE_WINDOW", False);
    XSetWMProtocols (text_box.display, text_box.window, &wm_delete_window, 1);

    while (1) {
        XEvent e;
        XNextEvent (text_box.display, & e);
        if (e.type == Expose) {
            draw_screen ();
        }
        else if (e.type == ConfigureNotify) {
            XConfigureEvent xce = e.xconfigure;
            if (xce.width != text_box.width ||
                xce.height != text_box.height) {
                text_box.width = xce.width;
                text_box.height = xce.height;
            }
            draw_screen ();
        }
        else if (e.type == ClientMessage) {
            if ((Atom)e.xclient.data.l[0] == wm_delete_window) {
                break;
            }
        }
    }
}


int main (int argc, char ** argv)
{
    text_box.coord_text = 0;
    text_box.coord_text_len = 0;
    x_connect ();
    create_window ();
    set_up_gc ();
    set_up_font ();
    event_loop ();
    return 0;
}

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This is a makefile for the C program:

CFLAGS=-g -Wall
XLIB=-L /usr/local/lib -l X11
XINC=-I /usr/local/include

text-box-coordinates:   text-box-coordinates.c
        $(CC) $(CFLAGS) -o $@ text-box-coordinates.c $(XLIB) $(XINC)

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