--- rxvt-unicode/src/perl/background	2012/06/05 14:04:58	1.7
+++ rxvt-unicode/src/perl/background	2012/06/05 19:32:29	1.13
@@ -1,8 +1,10 @@
 #! perl
 
+#:META:RESOURCE:$$:string:background expression
+
 our $EXPR = 'move load "/root/pix/das_fette_schwein.jpg", repeat_wrap, X, Y';
 $EXPR = '
-   rotate W, H, 50, 50, counter 1/60, repeat_mirror,
+   rotate W, H, 50, 50, counter 1/59.95, repeat_mirror,
    clip X, Y, W, H, repeat_mirror,
    load "/root/pix/das_fette_schwein.jpg"
 ';
@@ -15,6 +17,9 @@
 our ($bgdsl_self, $old, $new);
 our ($l, $t, $w, $h);
 
+# enforce at leats this time between updates
+our $MIN_INTERVAL = 1/100;
+
 {
    package urxvt::bgdsl; # background language
 
@@ -30,6 +35,7 @@
    }
 
    sub root() {
+      $new->{rootpmap_sensitive} = 1;
       die "root op not supported, exg, we need you";
    }
 
@@ -72,9 +78,7 @@
    sub blur($$$) {
       my ($rh, $rv, $img) = @_;
 
-      $img = $img->clone;
       $img->blur ($rh, $rv);
-      $img
    }
 
    sub contrast($$;$$;$) {
@@ -136,7 +140,18 @@
 sub recalculate {
    my ($self) = @_;
 
-   #TODO: rate limit calls
+   # rate limit evaluation
+
+   if ($self->{next_refresh} > urxvt::NOW) {
+      $self->{next_refresh_timer} = urxvt::timer->new->after ($self->{next_refresh} - urxvt::NOW)->cb (sub {
+         $self->recalculate;
+      });
+      return;
+   }
+
+   $self->{next_refresh} = urxvt::NOW + $MIN_INTERVAL;
+
+   # set environment to evaluate user expression
 
    local $bgdsl_self = $self;
 
@@ -146,9 +161,13 @@
    ($l, $t, $w, $h) =
       $self->get_geometry;
 
+   # evaluate user expression
+
    my $img = eval { $self->{expr}->() };
    warn $@ if $@;#d#
 
+   # if the expression is sensitive to external events, prepare reevaluation then
+
    my $repeat;
 
    if (my $again = $state->{again}) {
@@ -175,6 +194,15 @@
       $self->disable ("size_change");
    }
 
+   if (delete $state->{rootpmap_sensitive}) {
+      $repeat = 1;
+      $self->enable (rootpmap_change => sub { $_[0]->recalculate });
+   } else {
+      $self->disable ("rootpmap_change");
+   }
+
+   # clear stuff we no longer need
+
    %$old = ();
 
    unless ($repeat) {
@@ -182,6 +210,8 @@
       delete $self->{expr};
    }
 
+   # prepare and set background pixmap
+
    $img = $img->sub_rect (0, 0, $w, $h)
       if $img->w != $w || $img->h != $h;