Почему при изменении GdkFunktion в графическом контексте результат юзания етого контекста не изменяется???

/* GTK - The GIMP Toolkit * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Library General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Library General Public License for more details. * * You should have received a copy of the GNU Library General Public * License along with this library; if not, write to the * Free Software Foundation, Inc., 59 Temple Place - Suite 330, * Boston, MA 02111-1307, USA. */

#include <stdlib.h> #include <gtk/gtk.h>

/* Backing pixmap for drawing area */ static GdkPixmap *pixmap = NULL; static GdkGC *draw_gc;

/* Create a new backing pixmap of the appropriate size */ static gint configure_event( GtkWidget *widget, GdkEventConfigure *event ) { if (pixmap) g_object_unref (pixmap); if (draw_gc) g_object_unref (draw_gc);

pixmap = gdk_pixmap_new (widget->window, widget->allocation.width, widget->allocation.height, -1);

draw_gc = gdk_gc_new (widget->window); gdk_gc_copy (draw_gc, widget->style->black_gc); gdk_gc_set_function(draw_gc, GDK_INVERT);

gdk_draw_rectangle (pixmap, widget->style->white_gc, TRUE, 0, 0, widget->allocation.width, widget->allocation.height);

return TRUE; }

/* Redraw the screen from the backing pixmap */ static gint expose_event( GtkWidget *widget, GdkEventExpose *event ) { gdk_draw_drawable (widget->window, widget->style->fg_gc[GTK_WIDGET_STATE (widget)], pixmap, event->area.x, event->area.y, event->area.x, event->area.y, event->area.width, event->area.height);

return FALSE; }

/* Draw a rectangle on the screen */ static void draw_brush( GtkWidget *widget, gdouble x, gdouble y) { GdkRectangle update_rect;

update_rect.x = x - 5; update_rect.y = y - 5; update_rect.width = 10; update_rect.height = 10; gdk_draw_rectangle (pixmap, draw_gc, TRUE, update_rect.x, update_rect.y, update_rect.width, update_rect.height); gtk_widget_queue_draw_area (widget, update_rect.x, update_rect.y, update_rect.width, update_rect.height); }

static gint button_press_event( GtkWidget *widget, GdkEventButton *event ) { if (event->button == 1 && pixmap != NULL) draw_brush (widget, event->x, event->y);

return TRUE; }

/* GTK - The GIMP Toolkit
 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include <stdlib.h>
#include <gtk/gtk.h>

/* Backing pixmap for drawing area */
static GdkPixmap *pixmap = NULL;
static GdkGC *draw_gc;

/* Create a new backing pixmap of the appropriate size */
static gint configure_event( GtkWidget         *widget,
                             GdkEventConfigure *event )
{
  if (pixmap)
    g_object_unref (pixmap);
  if (draw_gc)
    g_object_unref (draw_gc);
    

  pixmap = gdk_pixmap_new (widget->window,
			   widget->allocation.width,
			   widget->allocation.height,
			   -1);

  draw_gc = gdk_gc_new (widget->window);
  gdk_gc_copy (draw_gc, widget->style->black_gc);
  gdk_gc_set_function(draw_gc, GDK_INVERT);

  gdk_draw_rectangle (pixmap,
		      widget->style->white_gc,
		      TRUE,
		      0, 0,
		      widget->allocation.width,
		      widget->allocation.height);

  return TRUE;
}

/* Redraw the screen from the backing pixmap */
static gint expose_event( GtkWidget      *widget,
                          GdkEventExpose *event )
{
  gdk_draw_drawable (widget->window,
		     widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
		     pixmap,
		     event->area.x, event->area.y,
		     event->area.x, event->area.y,
		     event->area.width, event->area.height);

  return FALSE;
}

/* Draw a rectangle on the screen */
static void draw_brush( GtkWidget *widget,
                        gdouble    x,
                        gdouble    y)
{
  GdkRectangle update_rect;

  update_rect.x = x - 15;
  update_rect.y = y - 15;
  update_rect.width = 30;
  update_rect.height = 30;
  gdk_draw_rectangle (pixmap,
		      draw_gc,
		      TRUE,
		      update_rect.x, update_rect.y,
		      update_rect.width, update_rect.height);
  gtk_widget_queue_draw_area (widget, 
		      update_rect.x, update_rect.y,
		      update_rect.width, update_rect.height);
}

static gint button_press_event( GtkWidget      *widget,
                                GdkEventButton *event )
{
  if (event->button == 1 && pixmap != NULL)
    draw_brush (widget, event->x, event->y);

  return TRUE;
}

static gint motion_notify_event( GtkWidget *widget,
                                 GdkEventMotion *event )
{
  int x, y;
  GdkModifierType state;

  if (event->is_hint)
    gdk_window_get_pointer (event->window, &x, &y, &state);
  else
    {
      x = event->x;
      y = event->y;
      state = event->state;
    }
    
  if (state & GDK_BUTTON1_MASK && pixmap != NULL)
    draw_brush (widget, x, y);
  
  return TRUE;
}

void quit ()
{
  exit (0);
}

int main( int   argc, 
          char *argv[] )
{
  GtkWidget *window;
  GtkWidget *drawing_area;
  GtkWidget *vbox;

  GtkWidget *button;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_widget_set_name (window, "Test Input");

  vbox = gtk_vbox_new (FALSE, 0);
  gtk_container_add (GTK_CONTAINER (window), vbox);
  gtk_widget_show (vbox);

  g_signal_connect (G_OBJECT (window), "destroy",
                    G_CALLBACK (quit), NULL);

  /* Create the drawing area */

  drawing_area = gtk_drawing_area_new ();
  gtk_widget_set_size_request (GTK_WIDGET (drawing_area), 200, 200);
  gtk_box_pack_start (GTK_BOX (vbox), drawing_area, TRUE, TRUE, 0);

  gtk_widget_show (drawing_area);

  /* Signals used to handle backing pixmap */

  g_signal_connect (G_OBJECT (drawing_area), "expose_event",
		    G_CALLBACK (expose_event), NULL);
  g_signal_connect (G_OBJECT (drawing_area),"configure_event",
		    G_CALLBACK (configure_event), NULL);

  /* Event signals */

  g_signal_connect (G_OBJECT (drawing_area), "motion_notify_event",
		    G_CALLBACK (motion_notify_event), NULL);
  g_signal_connect (G_OBJECT (drawing_area), "button_press_event",
		    G_CALLBACK (button_press_event), NULL);

  gtk_widget_set_events (drawing_area, GDK_EXPOSURE_MASK
			 | GDK_LEAVE_NOTIFY_MASK
			 | GDK_BUTTON_PRESS_MASK
			 | GDK_POINTER_MOTION_MASK
			 | GDK_POINTER_MOTION_HINT_MASK);

  /* .. And a quit button */
  button = gtk_button_new_with_label ("Quit");
  gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);

  g_signal_connect_swapped (G_OBJECT (button), "clicked",
			    G_CALLBACK (gtk_widget_destroy),
			    G_OBJECT (window));
  gtk_widget_show (button);

  gtk_widget_show (window);

  gtk_main ();

  return 0;
}

возможно, нужно текст сначала нарисовать на pixmap, а потом уже с помощью gc наложить на исходную картинку.

Я тоже к такому мнению пришёл. но чёто не совсем понимаю как ето реализовать технически. так что если не затруднит, плиз екзампл PS. Я новичок в графике на Gtk/Gdk

Хотя по приведённым выше примерам уже почти разобрался

Спасибо

Ну че, пример нужен еще?

Пока необходимости нет. Разве что для общего развития ;-)