transparent webkitgtk

#include <gtk/gtk.h>
#include <gdk/gdkx.h>
#include <gdk/gdkscreen.h>
#include <cairo.h>
#include <webkit/webkit.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);

static void location_cb(WebKitWebView *view, const char *uri, gpointer user_data)
{
    if(webkit_web_view_get_transparent(view)){
      fprintf(stdout,"TRANSPARENT\n");
    }else{
      fprintf(stdout,"NOT TRANSPARENT\n");
    }
    fprintf(stdout,"loaded\n");
    fflush(stdout);

}


int main(int argc, char **argv)
{
    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    GdkWindow *gwin;
    GtkWidget* webkit_player = NULL;

    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);


    webkit_player = webkit_web_view_new();
    webkit_web_view_set_transparent(WEBKIT_WEB_VIEW(webkit_player), TRUE);
    g_signal_connect(webkit_player, "load-finished", G_CALLBACK(location_cb), "file://test.html");

    gtk_container_add(GTK_CONTAINER(window), webkit_player);

    screen_changed(window, NULL, NULL);
    // load the uri
    webkit_web_view_load_string(WEBKIT_WEB_VIEW(webkit_player), "<html><style type='text/css'>body {background: rgba(0,255,0,0.1);}</style><head></head><body><h1>Hello World!</h1></body></html>", NULL, NULL, "file://");

    gtk_widget_show_all(window);
    gwin = gtk_widget_get_window(GTK_WIDGET(window));
    printf("the X11 id is %u\n", GDK_DRAWABLE_XID(gwin));

    gtk_main();

    return 0;
}


gboolean supports_alpha = TRUE;
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));
}