--- rxvt-unicode/src/perl/background	2012/06/10 11:53:32	1.45
+++ rxvt-unicode/src/perl/background	2012/06/10 13:32:55	1.46
@@ -1,7 +1,8 @@
 #! perl
 
 #:META:X_RESOURCE:%.expr:string:background expression
-#:META:X_RESOURCE:%.border.:boolean:respect the terminal border
+#:META:X_RESOURCE:%.border:boolean:respect the terminal border
+#:META:X_RESOURCE:%.interval:seconds:minimum time between updates
 
 #TODO: once, rootalign
 
@@ -13,6 +14,7 @@
 
    urxvt --background-expr 'background expression'
          --background-border
+         --background-interval seconds
 
 =head1 DESCRIPTION
 
@@ -191,6 +193,15 @@
 Specifying this flag changes the behaviour, so that the image only
 replaces the background of the character area.
 
+=item --background-interval seconds
+
+Since some operations in the underlying XRender extension can effetively
+freeze your X-server for prolonged time, this extension enforces a minimum
+time between updates, which is normally about 0.1 seconds.
+
+If you want to do updates more often, you can decrease this safety
+interval with this switch.
+
 =back
 
 =cut
@@ -200,7 +211,7 @@
 our ($x, $y, $w, $h);
 
 # enforce at least this interval between updates
-our $MIN_INTERVAL = 1/100;
+our $MIN_INTERVAL = 6/59.951;
 
 {
    package urxvt::bgdsl; # background language
@@ -555,6 +566,17 @@
 
    move 20, 30, ...
 
+=item align $xalign, $yalign, $img
+
+Aligns the image according to a factor - C<0> means the image is moved to
+the left or top edge (for C<$xalign> or C<$yalign>), C<0.5> means it is
+exactly centered and C<1> means it touches the right or bottom edge.
+
+Example: remove any visible border around an image, center it vertically but move
+it to the right hand side.
+
+   align 1, 0.5, pad $img
+
 =item center $img
 
 =item center $width, $height, $img
@@ -563,6 +585,10 @@
 the terminal window (or the box specified by C<$width> and C<$height> if
 given).
 
+Example: load an image and center it.
+
+  center pad load "mybg.png"
+
 =item rootalign $img
 
 Moves the image so that it appears glued to the screen as opposed to the
@@ -577,7 +603,7 @@
 Example: take the screen background and align it, giving the illusion of
 transparency as long as the window isn't in front of other windows.
 
-  rootalign root
+   rootalign root
 
 =cut
 
@@ -587,10 +613,18 @@
       $img
    }
 
+   sub align($;$$) {
+      my $img = pop;
+
+      move $_[0] * (TW - $img->w),
+           $_[1] * (TH - $img->h),
+           $img
+   }
+
    sub center($;$$) {
       my $img = pop;
       my $w = $_[0] || TW;
-      my $h = $_[0] || TH;
+      my $h = $_[1] || TH;
 
       move 0.5 * ($w - $img->w), 0.5 * ($h - $img->h), $img
    }
@@ -830,6 +864,8 @@
    $self->set_expr (parse_expr $expr);
    $self->{border} = $self->x_resource_boolean ("background.border");
 
+   $MIN_INTERVAL = $self->x_resource ("background.interval");
+
    ()
 }