Comment rendre l'arrière-plan de la fenêtre Gtk + transparent?

J'ai changé le alphademo exemple pour dessiner un bouton au lieu de le cercle rouge.

Cette application tire sur le bouton d'un 400x400 fenêtre transparente.

Lorsque vous cliquez sur la fenêtre de l'application affiche/masque la barre de titre.

#include <gtk/gtk.h>
#include <gdk/gdkscreen.h>
#include <cairo.h>
static void screen_changed(GtkWidget *widget, GdkScreen *old_screen, gpointer user_data);
static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer user_data);
static void clicked(GtkWindow *win, GdkEventButton *event, gpointer user_data);
int main(int argc, char **argv)
{
gtk_init(&argc, &argv);
GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 400, 400);
gtk_window_set_title(GTK_WINDOW(window), "Alpha Demo");
g_signal_connect(G_OBJECT(window), "delete-event", gtk_main_quit, NULL);
gtk_widget_set_app_paintable(window, TRUE);
g_signal_connect(G_OBJECT(window), "expose-event", G_CALLBACK(expose), NULL);
g_signal_connect(G_OBJECT(window), "screen-changed", G_CALLBACK(screen_changed), NULL);
gtk_window_set_decorated(GTK_WINDOW(window), FALSE);
gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);
g_signal_connect(G_OBJECT(window), "button-press-event", G_CALLBACK(clicked), NULL);
GtkWidget* fixed_container = gtk_fixed_new();
gtk_container_add(GTK_CONTAINER(window), fixed_container);
GtkWidget* button = gtk_button_new_with_label("button1");
gtk_widget_set_size_request(button, 100, 100);
gtk_container_add(GTK_CONTAINER(fixed_container), button);
screen_changed(window, NULL, NULL);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
gboolean supports_alpha = FALSE;
static void screen_changed(GtkWidget *widget, GdkScreen *old_screen, gpointer userdata)
{
/* To check if the display supports alpha channels, get the colormap */
GdkScreen *screen = gtk_widget_get_screen(widget);
GdkColormap *colormap = gdk_screen_get_rgba_colormap(screen);
if (!colormap)
{
printf("Your screen does not support alpha channels!\n");
colormap = gdk_screen_get_rgb_colormap(screen);
supports_alpha = FALSE;
}
else
{
printf("Your screen supports alpha channels!\n");
supports_alpha = TRUE;
}
gtk_widget_set_colormap(widget, colormap);
}
static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer userdata)
{
cairo_t *cr = gdk_cairo_create(widget->window);
if (supports_alpha)
cairo_set_source_rgba (cr, 1.0, 1.0, 1.0, 0.0); /* transparent */
else
cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* opaque white */
/* draw the background */
cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
cairo_paint (cr);
cairo_destroy(cr);
return FALSE;
}
static void clicked(GtkWindow *win, GdkEventButton *event, gpointer user_data)
{
/* toggle window manager frames */
gtk_window_set_decorated(win, !gtk_window_get_decorated(win));
}

Compilé sur Ubuntu 10.04:

gcc alpha.c -o alpha -I/usr/include/gtk-2.0 -I/usr/lib/gtk-2.0/include -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -lgtk-x11-2.0

Merci pour la réponse. Je réécrire le code en python + GTK3:

#!/usr/bin/python3
from gi.repository import Gtk
from gi.repository import Gdk
import cairo
supports_alpha = False
def screen_changed(widget, old_screen, userdata=None):
global supports_alpha
screen = widget.get_screen()
visual = screen.get_rgba_visual()
if visual is None:
print("Your screen does not support alpha channels!")
visual = screen.get_system_visual()
supports_alpha = False
else:
print("Your screen supports alpha channels!")
supports_alpha = True
widget.set_visual(visual)
def expose_draw(widget, event, userdata=None):
global supports_alpha
cr = Gdk.cairo_create(widget.get_window())
if supports_alpha:
print("setting transparent window")
cr.set_source_rgba(1.0, 1.0, 1.0, 0.0) 
else:
print("setting opaque window")
cr.set_source_rgb(1.0, 1.0, 1.0)
cr.set_operator(cairo.OPERATOR_SOURCE)
cr.paint()
return False
def clicked(window, event, userdata=None):
# toggle window manager frames
window.set_decorated(not window.get_decorated())
if __name__ == "__main__":
window = Gtk.Window()
window.set_position(Gtk.WindowPosition.CENTER)
window.set_default_size(400, 400)
window.set_title("Alpha Demo")
window.connect("delete-event", Gtk.main_quit)
window.set_app_paintable(True)
window.connect("draw", expose_draw)
window.connect("screen-changed", screen_changed)
window.set_decorated(False)
window.add_events(Gdk.EventMask.BUTTON_PRESS_MASK)
window.connect("button-press-event", clicked)
fixed_container = Gtk.Fixed()
window.add(fixed_container)
button = Gtk.Button.new_with_label("button1")
button.set_size_request(100, 100)
fixed_container.add(button)
screen_changed(window, None, None)
window.show_all()
Gtk.main()