urxvt-background(1) RXVT-UNICODE urxvt-background(1)

NAME

background - manage terminal background

SYNOPSIS

urxvt --background-expr 'background expression'
--background-border
--background-interval seconds

QUICK AND DIRTY CHEAT SHEET

Load a random jpeg image and tile the background with it without
scaling or anything else:

load "/path/to/img.jpg"

The same, but use mirroring/reflection instead of tiling:

mirror load "/path/to/img.jpg"

Load an image and scale it to exactly fill the terminal window:

scale keep { load "/path/to/img.jpg" }

Implement pseudo-transparency by using a suitably-aligned root pixmap
as window background:

rootalign root

Likewise, but keep a blurred copy:

rootalign keep { blur 10, root }

DESCRIPTION

This extension manages the terminal background by creating a picture
that is behind the text, replacing the normal background colour.

It does so by evaluating a Perl expression that calculates the image
on the fly, for example, by grabbing the root background or loading a
file.

While the full power of Perl is available, the operators have been
designed to be as simple as possible.

For example, to load an image and scale it to the window size, you
would use:

urxvt --background-expr 'scale keep { load "/path/to/mybg.png" }'

Or specified as a X resource:

URxvt.background.expr: scale keep { load "/path/to/mybg.png" }

THEORY OF OPERATION

At startup, just before the window is mapped for the first time, the
expression is evaluated and must yield an image. The image is then
extended as necessary to cover the whole terminal window, and is set
as a background pixmap.

If the image contains an alpha channel, then it will be used as-is in
visuals that support alpha channels (for example, for a compositing
manager). In other visuals, the terminal background colour will be
used to replace any transparency.

When the expression relies, directly or indirectly, on the window
size, position, the root pixmap, or a timer, then it will be
remembered. If not, then it will be removed.

If any of the parameters that the expression relies on changes (when
the window is moved or resized, its position or size changes; when
the root pixmap is replaced by another one the root background
changes; or when the timer elapses), then the expression will be
evaluated again.

For example, an expression such as "scale keep { load
"$HOME/mybg.png" }" scales the image to the window size, so it relies
on the window size and will be reevaluated each time it is changed,
but not when it moves for example. That ensures that the picture
always fills the terminal, even after its size changes.

EXPRESSIONS

Expressions are normal Perl expressions, in fact, they are Perl
blocks - which means you could use multiple lines and statements:

scale keep {
again 3600;
if (localtime now)[6]) {
return load "$HOME/weekday.png";
} else {
return load "$HOME/sunday.png";
}
}

This inner expression is evaluated once per hour (and whenever the
terminal window is resized). It sets sunday.png as background on
Sundays, and weekday.png on all other days.

Fortunately, we expect that most expressions will be much simpler,
with little Perl knowledge needed.

Basically, you always start with a function that "generates" an image
object, such as "load", which loads an image from disk, or "root",
which returns the root window background image:

load "$HOME/mypic.png"

The path is usually specified as a quoted string (the exact rules can
be found in the perlop manpage). The $HOME at the beginning of the
string is expanded to the home directory.

Then you prepend one or more modifiers or filtering expressions, such
as "scale":

scale load "$HOME/mypic.png"

Just like a mathematical expression with functions, you should read
these expressions from right to left, as the "load" is evaluated
first, and its result becomes the argument to the "scale" function.

Many operators also allow some parameters preceding the input image
that modify its behaviour. For example, "scale" without any
additional arguments scales the image to size of the terminal window.
If you specify an additional argument, it uses it as a scale factor
(multiply by 100 to get a percentage):

scale 2, load "$HOME/mypic.png"

This enlarges the image by a factor of 2 (200%). As you can see,
"scale" has now two arguments, the 2 and the "load" expression, while
"load" only has one argument. Arguments are separated from each other
by commas.

Scale also accepts two arguments, which are then separate factors for
both horizontal and vertical dimensions. For example, this halves the
image width and doubles the image height:

scale 0.5, 2, load "$HOME/mypic.png"

IF you try out these expressions, you might suffer from some
sluggishness, because each time the terminal is resized, it loads the
PNG image again and scales it. Scaling is usually fast (and
unavoidable), but loading the image can be quite time consuming. This
is where "keep" comes in handy:

scale 0.5, 2, keep { load "$HOME/mypic.png" }

The "keep" operator executes all the statements inside the braces
only once, or when it thinks the outcome might change. In other cases
it returns the last value computed by the brace block.

This means that the "load" is only executed once, which makes it much
faster, but also means that more memory is being used, because the
loaded image must be kept in memory at all times. In this expression,
the trade-off is likely worth it.

But back to effects: Other effects than scaling are also readily
available, for example, you can tile the image to fill the whole
window, instead of resizing it:

tile keep { load "$HOME/mypic.png" }

In fact, images returned by "load" are in "tile" mode by default, so
the "tile" operator is kind of superfluous.

Another common effect is to mirror the image, so that the same edges
touch:

mirror keep { load "$HOME/mypic.png" }

Another common background expression is:

rootalign root

This one first takes a snapshot of the screen background image, and
then moves it to the upper left corner of the screen (as opposed to
the upper left corner of the terminal window)- the result is pseudo-
transparency: the image seems to be static while the window is moved
around.

COLOUR SPECIFICATIONS

Whenever an operator expects a "colour", then this can be specified
in one of two ways: Either as string with an X11 colour
specification, such as:

"red" # named colour
"#f00" # simple rgb
"[50]red" # red with 50% alpha
"TekHVC:300/50/50" # anything goes

OR as an array reference with one, three or four components:

[0.5] # 50% gray, 100% alpha
[0.5, 0, 0] # dark red, no green or blur, 100% alpha
[0.5, 0, 0, 0.7] # same with explicit 70% alpha

CACHING AND SENSITIVITY

Since some operations (such as "load" and "blur") can take a long
time, caching results can be very important for a smooth operation.
Caching can also be useful to reduce memory usage, though, for
example, when an image is cached by "load", it could be shared by
multiple terminal windows running inside urxvtd.

"keep { ... }" caching

The most important way to cache expensive operations is to use "keep
{ ... }". The "keep" operator takes a block of multiple statements
enclosed by "{}" and keeps the return value in memory.

An expression can be "sensitive" to various external events, such as
scaling or moving the window, root background changes and timers.
Simply using an expression (such as "scale" without parameters) that
depends on certain changing values (called "variables"), or using
those variables directly, will make an expression sensitive to these
events - for example, using "scale" or "TW" will make the expression
sensitive to the terminal size, and thus to resizing events.

When such an event happens, "keep" will automatically trigger a
reevaluation of the whole expression with the new value of the
expression.

"keep" is most useful for expensive operations, such as "blur":

rootalign keep { blur 20, root }

This makes a blurred copy of the root background once, and on
subsequent calls, just root-aligns it. Since "blur" is usually quite
slow and "rootalign" is quite fast, this trades extra memory (for the
cached blurred pixmap) with speed (blur only needs to be redone when
root changes).

"load" caching

The "load" operator itself does not keep images in memory, but as
long as the image is still in memory, "load" will use the in-memory
image instead of loading it freshly from disk.

That means that this expression:

keep { load "$HOME/path..." }

Not only caches the image in memory, other terminal instances that
try to "load" it can reuse that in-memory copy.

REFERENCE

COMMAND LINE SWITCHES

--background-expr perl-expression
Specifies the Perl expression to evaluate.

--background-border
By default, the expression creates an image that fills the full
window, overwriting borders and any other areas, such as the
scrollbar.

Specifying this flag changes the behaviour, so that the image
only replaces the background of the character area.

--background-interval seconds
Since some operations in the underlying XRender extension can
effectively 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.

PROVIDERS/GENERATORS
These functions provide an image, by loading it from disk, grabbing
it from the root screen or by simply generating it. They are used as
starting points to get an image you can play with.

load $path
Loads the image at the given $path. The image is set to plane
tiling mode.

If the image is already in memory (e.g. because another terminal
instance uses it), then the in-memory copy is returned instead.

load_uc $path
Load uncached - same as load, but does not cache the image, which
means it is always loaded from the filesystem again, even if
another copy of it is in memory at the time.

root
Returns the root window pixmap, that is, hopefully, the
background image of your screen.

This function makes your expression root sensitive, that means it
will be reevaluated when the bg image changes.

solid $colour
solid $width, $height, $colour
Creates a new image and completely fills it with the given
colour. The image is set to tiling mode.

If $width and $height are omitted, it creates a 1x1 image, which
is useful for solid backgrounds or for use in filtering effects.

clone $img
Returns an exact copy of the image. This is useful if you want to
have multiple copies of the same image to apply different effects
to.

merge $img ...
Takes any number of images and merges them together, creating a
single image containing them all. The tiling mode of the first
image is used as the tiling mode of the resulting image.

This function is called automatically when an expression returns
multiple images.

TILING MODES

The following operators modify the tiling mode of an image, that is,
the way that pixels outside the image area are painted when the image
is used.

tile $img
Tiles the whole plane with the image and returns this new image -
or in other words, it returns a copy of the image in plane tiling
mode.

Example: load an image and tile it over the background, without
resizing. The "tile" call is superfluous because "load" already
defaults to tiling mode.

tile load "mybg.png"

mirror $img
Similar to tile, but reflects the image each time it uses a new
copy, so that top edges always touch top edges, right edges
always touch right edges and so on (with normal tiling, left
edges always touch right edges and top always touch bottom
edges).

Example: load an image and mirror it over the background,
avoiding sharp edges at the image borders at the expense of
mirroring the image itself

mirror load "mybg.png"

pad $img
Takes an image and modifies it so that all pixels outside the
image area become transparent. This mode is most useful when you
want to place an image over another image or the background
colour while leaving all background pixels outside the image
unchanged.

Example: load an image and display it in the upper left corner.
The rest of the space is left "empty" (transparent or whatever
your compositor does in alpha mode, else background colour).

pad load "mybg.png"

extend $img
Extends the image over the whole plane, using the closest pixel
in the area outside the image. This mode is mostly useful when
you use more complex filtering operations and want the pixels
outside the image to have the same values as the pixels near the
edge.

Example: just for curiosity, how does this pixel extension stuff
work?

extend move 50, 50, load "mybg.png"

VARIABLE VALUES

The following functions provide variable data such as the terminal
window dimensions. They are not (Perl-) variables, they just return
stuff that varies. Most of them make your expression sensitive to
some events, for example using "TW" (terminal width) means your
expression is evaluated again when the terminal is resized.

TX
TY Return the X and Y coordinates of the terminal window (the
terminal window is the full window by default, and the character
area only when in border-respect mode).

Using these functions makes your expression sensitive to window
moves.

These functions are mainly useful to align images to the root
window.

Example: load an image and align it so it looks as if anchored to
the background (that's exactly what "rootalign" does btw.):

move -TX, -TY, keep { load "mybg.png" }

TW
TH Return the width ("TW") and height ("TH") of the terminal window
(the terminal window is the full window by default, and the
character area only when in border-respect mode).

Using these functions makes your expression sensitive to window
resizes.

These functions are mainly useful to scale images, or to clip
images to the window size to conserve memory.

Example: take the screen background, clip it to the window size,
blur it a bit, align it to the window position and use it as
background.

clip move -TX, -TY, keep { blur 5, root }

FOCUS
Returns a boolean indicating whether the terminal window has
keyboard focus, in which case it returns true.

Using this function makes your expression sensitive to focus
changes.

A common use case is to fade the background image when the
terminal loses focus, often together with the "-fade" command
line option. In fact, there is a special function for just that
use case: "focus_fade".

Example: use two entirely different background images, depending
on whether the window has focus.

FOCUS ? keep { load "has_focus.jpg" } : keep { load "no_focus.jpg" }

now Returns the current time as (fractional) seconds since the epoch.

Using this expression does not make your expression sensitive to
time, but the next two functions do.

again $seconds
When this function is used the expression will be reevaluated
again in $seconds seconds.

Example: load some image and rotate it according to the time of
day (as if it were the hour pointer of a clock). Update this
image every minute.

again 60;
rotate 50, 50, (now % 86400) * -72 / 8640, scale keep { load "myclock.png" }

counter $seconds
Like "again", but also returns an increasing counter value,
starting at 0, which might be useful for some simple animation
effects.

SHAPE CHANGING OPERATORS

The following operators modify the shape, size or position of the
image.

clip $img
clip $width, $height, $img
clip $x, $y, $width, $height, $img
Clips an image to the given rectangle. If the rectangle is
outside the image area (e.g. when $x or $y are negative) or the
rectangle is larger than the image, then the tiling mode defines
how the extra pixels will be filled.

If $x and $y are missing, then 0 is assumed for both.

If $width and $height are missing, then the window size will be
assumed.

Example: load an image, blur it, and clip it to the window size
to save memory.

clip keep { blur 10, load "mybg.png" }

scale $img
scale $size_factor, $img
scale $width_factor, $height_factor, $img
Scales the image by the given factors in horizontal ($width) and
vertical ($height) direction.

If only one factor is given, it is used for both directions.

If no factors are given, scales the image to the window size
without keeping aspect.

resize $width, $height, $img
Resizes the image to exactly $width times $height pixels.

fit $img
fit $width, $height, $img
Fits the image into the given $width and $height without changing
aspect, or the terminal size. That means it will be shrunk or
grown until the whole image fits into the given area, possibly
leaving borders.

cover $img
cover $width, $height, $img
Similar to "fit", but shrinks or grows until all of the area is
covered by the image, so instead of potentially leaving borders,
it will cut off image data that doesn't fit.

move $dx, $dy, $img
Moves the image by $dx pixels in the horizontal, and $dy pixels
in the vertical.

Example: move the image right by 20 pixels and down by 30.

move 20, 30, ...

align $xalign, $yalign, $img
Aligns the image according to a factor - 0 means the image is
moved to the left or top edge (for $xalign or $yalign), 0.5 means
it is exactly centered and 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

center $img
center $width, $height, $img
Centers the image, i.e. the center of the image is moved to the
center of the terminal window (or the box specified by $width and
$height if given).

Example: load an image and center it.

center keep { pad load "mybg.png" }

rootalign $img
Moves the image so that it appears glued to the screen as opposed
to the window. This gives the illusion of a larger area behind
the window. It is exactly equivalent to "move -TX, -TY", that is,
it moves the image to the top left of the screen.

Example: load a background image, put it in mirror mode and root
align it.

rootalign keep { mirror load "mybg.png" }

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

rotate $center_x, $center_y, $degrees, $img
Rotates the image clockwise by $degrees degrees, around the point
at $center_x and $center_y (specified as factor of image
width/height).

Example: rotate the image by 90 degrees around its center.

rotate 0.5, 0.5, 90, keep { load "$HOME/mybg.png" }

COLOUR MODIFICATIONS

The following operators change the pixels of the image.

tint $color, $img
Tints the image in the given colour.

Example: tint the image red.

tint "red", load "rgb.png"

Example: the same, but specify the colour by component.

tint [1, 0, 0], load "rgb.png"

shade $factor, $img
Shade the image by the given factor.

contrast $factor, $img
contrast $r, $g, $b, $img
contrast $r, $g, $b, $a, $img
Adjusts the contrast of an image.

The first form applies a single $factor to red, green and blue,
the second form applies separate factors to each colour channel,
and the last form includes the alpha channel.

Values from 0 to 1 lower the contrast, values higher than 1
increase the contrast.

Due to limitations in the underlying XRender extension, lowering
contrast also reduces brightness, while increasing contrast
currently also increases brightness.

brightness $bias, $img
brightness $r, $g, $b, $img
brightness $r, $g, $b, $a, $img
Adjusts the brightness of an image.

The first form applies a single $bias to red, green and blue, the
second form applies separate biases to each colour channel, and
the last form includes the alpha channel.

Values less than 0 reduce brightness, while values larger than 0
increase it. Useful range is from -1 to 1 - the former results in
a black, the latter in a white picture.

Due to idiosyncrasies in the underlying XRender extension, biases
less than zero can be very slow.

You can also try the experimental(!) "muladd" operator.

muladd $mul, $add, $img # EXPERIMENTAL
First multiplies the pixels by $mul, then adds $add. This can be
used to implement brightness and contrast at the same time, with
a wider value range than contrast and brightness operators.

Due to numerous bugs in XRender implementations, it can also
introduce a number of visual artifacts.

Example: increase contrast by a factor of $c without changing
image brightness too much.

muladd $c, (1 - $c) * 0.5, $img

blur $radius, $img
blur $radius_horz, $radius_vert, $img
Gaussian-blurs the image with (roughly) $radius pixel radius. The
radii can also be specified separately.

Blurring is often very slow, at least compared or other
operators. Larger blur radii are slower than smaller ones, too,
so if you don't want to freeze your screen for long times, start
experimenting with low values for radius (<5).

focus_fade $img
focus_fade $factor, $img
focus_fade $factor, $color, $img
Fades the image by the given factor (and colour) when focus is
lost (the same as the "-fade"/"-fadecolor" command line options,
which also supply the default values for "factor" and $color.
Unlike with "-fade", the $factor is a real value, not a
percentage value (that is, 0..1, not 0..100).

Example: do the right thing when focus fading is requested.

focus_fade load "mybg.jpg";

OTHER STUFF

Anything that didn't fit any of the other categories, even after
applying force and closing our eyes.

keep { ... }
This operator takes a code block as argument, that is, one or
more statements enclosed by braces.

The trick is that this code block is only evaluated when the
outcome changes - on other calls the "keep" simply returns the
image it computed previously (yes, it should only be used with
images). Or in other words, "keep" caches the result of the code
block so it doesn't need to be computed again.

This can be extremely useful to avoid redoing slow operations -
for example, if your background expression takes the root
background, blurs it and then root-aligns it it would have to
blur the root background on every window move or resize.

Another example is "load", which can be quite slow.

In fact, urxvt itself encloses the whole expression in some kind
of "keep" block so it only is reevaluated as required.

Putting the blur into a "keep" block will make sure the blur is
only done once, while the "rootalign" is still done each time the
window moves.

rootalign keep { blur 10, root }

This leaves the question of how to force reevaluation of the
block, in case the root background changes: If expression inside
the block is sensitive to some event (root background changes,
window geometry changes), then it will be reevaluated
automatically as needed.

OLD BACKGROUND IMAGE SETTINGS

This extension also provides support for the old options/resources
and OSC sequences for setting a background image. These settings are
deprecated and will be removed in future versions.

OPTIONS AND RESOURCES

-pixmap file[;oplist]
backgroundPixmap: file[;oplist]
Use the specified image file as the window's background and also
optionally specify a colon separated list of operations to modify
it. Note that you may need to quote the ";" character when using
the command line option, as ";" is usually a metacharacter in
shells. Supported operations are:

WxH+X+Y
sets scale and position. "W" / "H" specify the
horizontal/vertical scale (percent), and "X" / "Y" locate the
image centre (percent). A scale of 0 disables scaling.

op=tile
enables tiling

op=keep-aspect
maintain the image aspect ratio when scaling

op=root-align
use the position of the terminal window relative to the root
window as the image offset, simulating a root window
background

The default scale and position setting is "100x100+50+50".
Alternatively, a predefined set of templates can be used to
achieve the most common setups:

style=tiled
the image is tiled with no scaling. Equivalent to
0x0+0+0:op=tile

style=aspect-stretched
the image is scaled to fill the whole window maintaining the
aspect ratio and centered. Equivalent to
100x100+50+50:op=keep-aspect

style=stretched
the image is scaled to fill the whole window. Equivalent to
100x100

style=centered
the image is centered with no scaling. Equivalent to
0x0+50+50

style=root-tiled
the image is tiled with no scaling and using 'root'
positioning. Equivalent to 0x0:op=tile:op=root-align

If multiple templates are specified the last one wins. Note that
a template overrides all the scale, position and operations
settings.

If used in conjunction with pseudo-transparency, the specified
image will be blended over the transparent background using
alpha-blending.

-tr|+tr
transparent: boolean
Turn on/off pseudo-transparency by using the root pixmap as
background.

-tint colour
tintColor: colour
Tint the transparent background with the given colour. Note that
a black tint yields a completely black image while a white tint
yields the image unchanged.

-sh number
shading: number
Darken (0 .. 99) or lighten (101 .. 200) the transparent
background. A value of 100 means no shading.

-blr HxV
blurRadius: HxV
Apply gaussian blur with the specified radius to the transparent
background. If a single number is specified, the vertical and
horizontal radii are considered to be the same. Setting one of
the radii to 1 and the other to a large number creates
interesting effects on some backgrounds. The maximum radius value
is 128. An horizontal or vertical radius of 0 disables blurring.

OSC sequences

This extension will react to the following OSC sequences. Note that
this extension will not be autoloaded when these are used currently,
so to make urxvt recognize them, you have to enable the "background"
extension. One way to achieve that is to use the "--background-expr
''" command line argument or by specifying an empty
"URxvt.background.expr:"> resource.

"ESC ] 705 ; Pt ST" Change transparent background tint colour to
"Pt".
"ESC ] 20 ; Pt ST" Change/Query background image parameters: the
value of "Pt" can be one of the following commands:
"?" display scale and position in the title

";WxH+X+Y"
change scale and/or position

"FILE;WxH+X+Y"
change background image

9.31 2023-10-24 urxvt-background(1)