A program that takes: font, string, and renders accordingly using Xlib. Almost a verbatim copy of the one at: http://www.lemoda.net/c/xlib-text-box/index.html

xrenderstring.c

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

/* The window which contains the text. */

struct
{
  int width;
  int height;
  char *text;
  int 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);
  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. */

const char *fontname;

static void
set_up_font ()
{
  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);
}

/* Draw the window. */

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

  /* Centre the text in the middle of the box. */

  XTextExtents (text_box.font, text_box.text, text_box.text_len,
                &direction, &ascent, &descent, &overall);
  x = (text_box.width - overall.width) / 2;
  y = text_box.height / 2 + (ascent - descent) / 2;
  XClearWindow (text_box.display, text_box.window);
  XDrawString (text_box.display, text_box.window, text_box.gc,
               x, y, text_box.text, text_box.text_len);
}

/* Loop over events. */

static void
event_loop ()
{
  while (1)
    {
      XEvent e;
      XNextEvent (text_box.display, &e);
      if (e.type == Expose)
        {
          draw_screen ();
        }
    }
}

int
main (int argc, char **argv)
{
  if (argc < 3)
    return 0;

  fontname = argv[1];
  text_box.text = argv[2];
  text_box.text_len = strlen (text_box.text);
  x_connect ();
  create_window ();
  set_up_gc ();
  set_up_font ();
  event_loop ();
  return 0;
}