draw-lines.c

#include <gtk/gtk.h>

static cairo_surface_t *tmp_surface = NULL;
static cairo_surface_t *base_surface = NULL;

static gdouble ax;
static gdouble ay;

static void
clear_surface (cairo_surface_t *surface)
{
  cairo_t *cr;

  cr = cairo_create (surface);

  cairo_set_source_rgb (cr, 1, 1, 1);
  cairo_paint (cr);

  cairo_destroy (cr);
}

static void
init_surface(cairo_surface_t **surface, GtkWidget *widget)
{
  if (*surface)
    cairo_surface_destroy (*surface);

  *surface = gdk_window_create_similar_surface (gtk_widget_get_window (widget),
                                                CAIRO_CONTENT_COLOR,
                                                gtk_widget_get_allocated_width (widget),
                                                gtk_widget_get_allocated_height (widget));

  clear_surface (*surface);
}

static gboolean
configure_event_cb (GtkWidget         *widget,
                    GdkEventConfigure *event,
                    gpointer           data)
{
  init_surface(&tmp_surface, widget);
  init_surface(&base_surface, widget);

  return TRUE;
}

static gboolean
draw_cb (GtkWidget *widget,
         cairo_t   *cr,
         gpointer   data)
{
  cairo_set_source_surface (cr, tmp_surface, 0, 0);
  cairo_paint (cr);

  return FALSE;
}

static void
draw_brush (GtkWidget *widget,
            gdouble    x,
            gdouble    y)
{
  cairo_t * cr = cairo_create (tmp_surface);

  cairo_move_to (cr, ax, ay);
  cairo_line_to (cr, x, y);
  cairo_stroke (cr);

  cairo_destroy (cr);

  gtk_widget_queue_draw_area (widget, 0, 0, 100, 100);
}

static gboolean
button_press_event_cb (GtkWidget      *widget,
                       GdkEventButton *event,
                       gpointer        data)
{
  cairo_t *cr = cairo_create (tmp_surface);
  cairo_set_source_surface (cr, base_surface, 0, 0);
  cairo_paint (cr);
  cairo_destroy (cr);
  
  ax = event->x; ay = event->y;
  draw_brush (widget, event->x, event->y);

  return TRUE;
}

static gboolean
button_release_event_cb (GtkWidget      *widget,
                         GdkEventButton *event,
                         gpointer        data)
{
  cairo_t *cr = cairo_create (base_surface);
  cairo_set_source_surface (cr, tmp_surface, 0, 0);
  cairo_paint (cr);
  cairo_destroy (cr);

  return TRUE;
}

static gboolean
motion_notify_event_cb (GtkWidget      *widget,
                        GdkEventMotion *event,
                        gpointer        data)
{
  if (event->state & GDK_BUTTON1_MASK)
    {
      cairo_t *cr = cairo_create (tmp_surface);
      cairo_set_source_surface (cr, base_surface, 0, 0);
      cairo_paint (cr);
      cairo_destroy (cr);
      
      draw_brush (widget, event->x, event->y);
    }

  return TRUE;
}

static void
close_window (void)
{
  gtk_main_quit ();
}

static void
activate (GtkApplication *app,
          gpointer        user_data)
{
  GtkWidget *window;
  GtkWidget *frame;
  GtkWidget *drawing_area;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Drawing Area");

  g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);

  gtk_container_set_border_width (GTK_CONTAINER (window), 8);

  frame = gtk_frame_new (NULL);
  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
  gtk_container_add (GTK_CONTAINER (window), frame);

  drawing_area = gtk_drawing_area_new ();

  gtk_widget_set_size_request (drawing_area, 100, 100);

  gtk_container_add (GTK_CONTAINER (frame), drawing_area);

  g_signal_connect (drawing_area, "draw",
                    G_CALLBACK (draw_cb), NULL);
  g_signal_connect (drawing_area,"configure-event",
                    G_CALLBACK (configure_event_cb), NULL);
  g_signal_connect (drawing_area, "motion-notify-event",
                    G_CALLBACK (motion_notify_event_cb), NULL);
  g_signal_connect (drawing_area, "button-press-event",
                    G_CALLBACK (button_press_event_cb), NULL);
  g_signal_connect (drawing_area, "button-release-event",
                    G_CALLBACK (button_release_event_cb), NULL);

  gtk_widget_set_events (drawing_area, gtk_widget_get_events (drawing_area)
			 | GDK_BUTTON_PRESS_MASK
			 | GDK_BUTTON_RELEASE_MASK
			 | GDK_POINTER_MOTION_MASK);

  gtk_widget_show_all (window);
}

int
main (int    argc,
      char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}