Drawing on the X root window

问题:

I'd like to be able to draw on the root window in Linux. I.e. make an OSD.

I'm using Gnome.

Code samples or links to them would be appreciated.

回答1:

It is possible, but you will not see anything in GNOME. Nautilus, GNOME's file manager, opens its own window on top of root X window to display icons. Because of that the root X window is fully covered... so there is no point in drawing on it.

If you want to make OSD, either you should use a library like XOSD, or open your own X window and make it translucent. In fact, XOSD's source code should be a good example of how to do this.

Whole library seems to be implemented in one file: xosd.c.

回答2:

use X11::Protocol;

my $x = X11::Protocol->new();
my $desktop;

my ($root,undef,@kids)=$x->QueryTree($x->{'root'});
printf "%10x:\tRoot\n", $root;
foreach (@kids){
my $gdkw = Gtk2::Gdk::Window->foreign_new($_);
printf ("%10x:\tDesktop\n",$gdkw->get_xid),$desktop=$gdkw,last if $gdkw->get_type_hint eq 'desktop';
}
$desktop=Gtk2::Gdk::Window->foreign_new($root) if ! $desktop;
#------------------------------------------

I can find desktop, verified by xwininfo. But, I lost the code which can draw desktop, seems used "set_back_pixmap".

Now cairo can draw on any windows very simply, just use

$cr = Gtk2::Gdk::Cairo::Context->create ($drawable);

But, this does not work on desktop. Perhaps due to kernel update? Or I messed up now on Ubuntu 10.04-3.