test1.c

/*
 * Example: In some fonts (e.g. Ubuntu Mono) if you render a combining
 *          code point (e.g. U+0301) without a preceding code point
 *          then U+25CC is used as preceding code point.
 * 
 * Compile and Link with
 *   gcc  $( pkg-config --cflags --libs pangocairo ) -o test1 test1.c 
 */
#include <cairo.h>
#include <pango/pangocairo.h>
#include <assert.h>

/* Unicode code points to UTF-8 code-unit(s) */
#define U002D  "\x2D"
#define U0061  "\x61"
#define U0301  "\xCC\x81"

static char const * const text1 = U0061 U0301 U002D;  /* "á-" in UTF-8 encoding  */
static char const * const text2 = U0301 U002D;        /* " ́-" in UTF-8 encoding */

int main (void) {
  cairo_surface_t *s = cairo_image_surface_create( CAIRO_FORMAT_RGB24, 200, 200);
  assert(NULL!=s);

  cairo_t *cr = cairo_create(s);          assert(NULL!=s);
  cairo_set_source_rgb(cr,1.0,1.0,1.0);   cairo_paint(cr); /* background */
  cairo_set_source_rgb(cr,0.0,0.0,0.0);                    /* font color */

  PangoFontDescription *fd = pango_font_description_new(); assert(NULL!=fd);
  pango_font_description_set_family(fd,"Ubuntu Mono");
  pango_font_description_set_absolute_size(fd, 30*PANGO_SCALE);

  PangoLayout *layout = pango_cairo_create_layout(cr); assert(NULL!=layout);
  pango_layout_set_font_description(layout,fd);

  pango_layout_set_text(layout,text1,-1); cairo_move_to(cr,10,50); 
  pango_cairo_show_layout_line(cr,pango_layout_get_line(layout,0));

  pango_layout_set_text(layout,text2,-1); cairo_move_to(cr,10,100); 
  pango_cairo_show_layout_line(cr,pango_layout_get_line(layout,0));

  g_object_unref(layout); pango_font_description_free(fd); cairo_destroy(cr);

  cairo_surface_write_to_png(s,"test1.png");
  cairo_surface_destroy(s);
}