如何使Gtk窗口背景透明？

我想使Gtk窗口的背景透明,以便只有窗口中的窗口小部件可见.我发现了几个教程：

http://mikehearn.wordpress.com/2006/03/26/gtk-windows-with-alpha-channels/

http://macslow.thepimp.net/?p=26

但他们似乎都听“暴露”事件,然后委托开罗做渲染.这意味着添加到窗口的其他小部件不会被渲染(例如,我已经尝试向窗口中添加一个按钮).

我看到GtkWidget有一个方法modify-bg：http://library.gnome.org/devel/gtk/stable/GtkWidget.html#gtk-widget-modify-bg

但是,GdkColor似乎没有接受透明度参数：http://library.gnome.org/devel/gdk/stable/gdk-Colormaps-and-Colors.html

我也尝试过GtkWindow.set_opacity方法,但这也设置了窗口内容的不透明度,这不是我想要的.

我会感谢任何人都可以提供的任何指导.

解决方法

我改变了 alphademo的例子来绘制一个按钮而不是红色的圆圈.

该应用程序在400×400透明窗口上绘制按钮.

当您点击窗口时,应用程序将显示/隐藏标题栏.

#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,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,gpointer userdata)
{
   cairo_t *cr = gdk_cairo_create(widget->window);

    if (supports_alpha)
        cairo_set_source_rgba (cr,1.0,0.0); /* transparent */
    else
        cairo_set_source_rgb (cr,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,gpointer user_data)
{
    /* toggle window manager frames */
    gtk_window_set_decorated(win,!gtk_window_get_decorated(win));
}

编译在Ubuntu 10.04上：

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