The Cairo graphics tutorial -------Text in Cairo

In this part of the Cairo graphics tutorial, we will work with text.

Soulmate

In the first example, we will display some lyrics on the GTK+ window.

#include <cairo.h>#include <gtk/gtk.h>static gbooleanon_expose_event(GtkWidget *widget,    GdkEventExpose *event,    gpointer data){  cairo_t *cr;  cr = gdk_cairo_create(widget->window);  cairo_set_source_rgb(cr, 0.1, 0.1, 0.1);   cairo_select_font_face(cr, "Purisa",      CAIRO_FONT_SLANT_NORMAL,      CAIRO_FONT_WEIGHT_BOLD);  cairo_set_font_size(cr, 13);  cairo_move_to(cr, 20, 30);  cairo_show_text(cr, "Most relationships seem so transitory");    cairo_move_to(cr, 20, 60);  cairo_show_text(cr, "They're all good but not the permanent one");  cairo_move_to(cr, 20, 120);  cairo_show_text(cr, "Who doesn't long for someone to hold");  cairo_move_to(cr, 20, 150);  cairo_show_text(cr, "Who knows how to love you without being told");  cairo_move_to(cr, 20, 180);  cairo_show_text(cr, "Somebody tell me why I'm on my own");  cairo_move_to(cr, 20, 210);  cairo_show_text(cr, "If there's a soulmate for everyone");  cairo_destroy(cr);  return FALSE;}int main (int argc, char *argv[]){  GtkWidget *window;  gtk_init(&argc, &argv);  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);  g_signal_connect(window, "expose-event",      G_CALLBACK(on_expose_event), NULL);  g_signal_connect(window, "destroy",      G_CALLBACK(gtk_main_quit), NULL);  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);  gtk_window_set_default_size(GTK_WINDOW(window), 420, 250);   gtk_window_set_title(GTK_WINDOW(window), "Soulmate");  gtk_widget_set_app_paintable(window, TRUE);  gtk_widget_show_all(window);  gtk_main();  return 0;}

In this example, we display part of the lyrics from the Natasha Bedingfields Soulmate song.

 cairo_select_font_face(cr, "Purisa",    CAIRO_FONT_SLANT_NORMAL,    CAIRO_FONT_WEIGHT_BOLD);

Here we select the font face. The function takes three parameters, the font family, font slant and the font weight.

 cairo_set_font_size(cr, 13);

Here we specify the font size.

 cairo_move_to(cr, 20, 30); cairo_show_text(cr, "Most relationships seem so transitory"); 

We display the text on the window by specifying the position of the text and calling thecairo_show_text() function.

Figure: Soulmate

Letter by letter

In this effect, we will display a text letter by letter. The letters will be drawn with some delay.

#include <cairo.h>#include <gtk/gtk.h>gpointer text[7] = { "Z", "e", "t", "C", "o", "d", "e" };gboolean timer = TRUE;static gbooleanon_expose_event(GtkWidget *widget,    GdkEventExpose *event,    gpointer data){  cairo_t *cr;  cairo_text_extents_t extents;  static gint count = 0;  cr = gdk_cairo_create(widget->window);  cairo_select_font_face(cr, "Courier",      CAIRO_FONT_SLANT_NORMAL,      CAIRO_FONT_WEIGHT_BOLD);  cairo_set_font_size(cr, 35);  cairo_set_source_rgb(cr, 0.2, 0.2, 0.2);   gint i;  gint x = 0;  for (i = 0; i < count; i++) {      cairo_text_extents(cr, text[i], &extents);      x += extents.width + 2;      cairo_move_to(cr, x + 30, 50);      cairo_show_text(cr, text[i]);    }  count++;  if (count == 8) {      timer = FALSE;      count = 0;  }  cairo_destroy(cr);  return FALSE;}static gbooleantime_handler (GtkWidget *widget){  if (widget->window == NULL) return FALSE;  if (!timer) return FALSE;  gtk_widget_queue_draw(widget);  return TRUE;}int main (int argc, char *argv[]){  GtkWidget *window;  gtk_init(&argc, &argv);  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);  g_signal_connect(window, "expose-event",      G_CALLBACK(on_expose_event), NULL);  g_signal_connect(window, "destroy",      G_CALLBACK(gtk_main_quit), NULL);  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);  gtk_window_set_default_size(GTK_WINDOW(window), 300, 90);   gtk_window_set_title(GTK_WINDOW(window), "ZetCode");  gtk_widget_set_app_paintable(window, TRUE);  g_timeout_add(1000, (GSourceFunc) time_handler, (gpointer) window);  gtk_widget_show_all(window);  gtk_main();  return 0;}

In our example, we will draw the "ZetCode" string onto the GTK+ window letter by letter with some delay.

 gpointer text[7] = { "Z", "e", "t", "C", "o", "d", "e" };

We create an array of strings.

 cairo_select_font_face(cr, "Courier",    CAIRO_FONT_SLANT_NORMAL,    CAIRO_FONT_WEIGHT_BOLD);

We select a Courier font face.

 for (i = 0; i < count; i++) {    cairo_text_extents(cr, text[i], &extents);    x += extents.width + 2;    cairo_move_to(cr, x + 30, 50);    cairo_show_text(cr, text[i]);   }

Here we draw the text letter by letter. The extents.width gives us the width of the current letter.

Figure: ZetCode

Puff

In the following example, we create a puff effect. The example will display a growing centered text, that will gradully fade out from some point. This is a very common effect, which you can often see in flash animations.

#include <cairo.h>#include <gtk/gtk.h>gpointer text[7] = { "Z", "e", "t", "C", "o", "d", "e" };gboolean timer = TRUE;static gbooleanon_expose_event(GtkWidget *widget,    GdkEventExpose *event,    gpointer data){  cairo_t *cr;  cairo_text_extents_t extents;  static gdouble alpha = 1.0;  static gdouble size = 1;  gint x = widget->allocation.width / 2;  gint y = widget->allocation.height / 2;  cr = gdk_cairo_create(widget->window);  cairo_set_source_rgb(cr, 0.5, 0, 0);   cairo_paint(cr);  cairo_select_font_face(cr, "Courier",      CAIRO_FONT_SLANT_NORMAL,      CAIRO_FONT_WEIGHT_BOLD);  size += 0.8;  if (size > 20) {      alpha -= 0.01;  }  cairo_set_font_size(cr, size);  cairo_set_source_rgb(cr, 1, 1, 1);   cairo_text_extents(cr, "ZetCode", &extents);  cairo_move_to(cr, x - extents.width/2, y);  cairo_text_path(cr, "ZetCode");  cairo_clip(cr);  cairo_stroke(cr);  cairo_paint_with_alpha(cr, alpha);  if (alpha <= 0) {      timer = FALSE;  }  cairo_destroy(cr);  return FALSE;}static gbooleantime_handler (GtkWidget *widget){  if (widget->window == NULL) return FALSE;  if (!timer) return FALSE;  gtk_widget_queue_draw(widget);  return TRUE;}int main (int argc, char *argv[]){  GtkWidget *window;  gtk_init(&argc, &argv);  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);  g_signal_connect(window, "expose-event",      G_CALLBACK(on_expose_event), NULL);  g_signal_connect(window, "destroy",      G_CALLBACK(gtk_main_quit), NULL);  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);  gtk_window_set_default_size(GTK_WINDOW(window), 350, 200);   gtk_window_set_title(GTK_WINDOW(window), "puff");  gtk_widget_set_app_paintable(window, TRUE);  g_timeout_add(14, (GSourceFunc) time_handler, (gpointer) window);  gtk_widget_show_all(window);  gtk_main();  return 0;}

The example creates a growing and fading text on the GTK+ window.

 gint x = widget->allocation.width / 2; gint y = widget->allocation.height / 2;

Coordinates of the middle point.

 cairo_set_source_rgb(cr, 0.5, 0, 0);  cairo_paint(cr);

We set the background color to dark red color.

 size += 0.8;

Each cycle, the font size will grow by 0.8 units.

 if (size > 20) {     alpha -= 0.01; }

The fading out begins after the font size is bigger than 20.

 cairo_text_extents(cr, "ZetCode", &extents);

We get the text metrics.

 cairo_move_to(cr, x - extents.width/2, y);

We use the text metrics to center the text on the window.

 cairo_text_path(cr, "ZetCode"); cairo_clip(cr);

We get the path of the text and set the current clip region to it.

 cairo_stroke(cr); cairo_paint_with_alpha(cr, alpha);

We paint the current path with and take alpha value into account.

Figure: Puff

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This chapter covered text in Cairo.