How to make Gtk+ window background transparent?
Thanks for the answer. I rewrite the code in python + GTK3:
#!/usr/bin/env python3
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk, 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()
Thanks for the code, just what i was looking for though it needs to be modified to work GTK3. Also the expose-event needs to be changed to a 'draw' event to get it working. So here's my code contribution modified for GTK3:
#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_draw(GtkWidget *widget, GdkEventExpose *event, gpointer userdata);
static void clicked(GtkWindow *window, 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), "draw", G_CALLBACK(expose_draw), 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) {
GdkScreen *screen = gtk_widget_get_screen(widget);
GdkVisual *visual = gdk_screen_get_rgba_visual(screen);
if (!visual) {
printf("Your screen does not support alpha channels!\n");
visual = gdk_screen_get_system_visual(screen);
supports_alpha = FALSE;
} else {
printf("Your screen supports alpha channels!\n");
supports_alpha = TRUE;
}
gtk_widget_set_visual(widget, visual);
}
static gboolean expose_draw(GtkWidget *widget, GdkEventExpose *event, gpointer userdata) {
cairo_t *cr = gdk_cairo_create(gtk_widget_get_window(widget));
if (supports_alpha) {
printf("setting transparent window\n");
cairo_set_source_rgba (cr, 1.0, 1.0, 1.0, 0.0);
} else {
printf("setting opaque window\n");
cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
}
cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
cairo_paint (cr);
cairo_destroy(cr);
return FALSE;
}
static void clicked(GtkWindow *window, GdkEventButton *event, gpointer user_data) {
/* toggle window manager frames */
gtk_window_set_decorated(window, !gtk_window_get_decorated(window));
}
Here's how i compiled it on Ubuntu 15.04:
gcc alpha.c -o alpha `pkg-config --cflags --libs glib-2.0` `pkg-config --cflags --libs gtk+-3.0`
Hopefully this helps out someone else trying to get it working on GTK3.
I changed the alphademo example to draw a button instead of the red circle.
This application draws the button on a 400x400 transparent window.
When you click on the window the application shows/hides the title bar.
#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));
}
Compiled on 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