Überzug

Überzug is a command line util which allows to draw images on terminals by using child windows.

Advantages to w3mimgdisplay:

• no race conditions as a new window is created to display images
• expose events will be processed,
  so images will be redrawn on switch workspaces
• tmux support (excluding multi pane windows)
• terminals without the WINDOWID environment variable are supported
• chars are used as position - and size unit
• no memory leak (/ unlimited cache)

Overview

• Dependencies
• Installation
• Communication
  • Command formats
  • Actions
    • Add
    • Remove
  • Libraries
    • Bash (deprecated)
    • Python
    • Python Urwid
  • Examples

Dependencies

Libraries used in the c extension:

• python
• X11
• Xext
• XRes

There are also other direct dependencies,
but they will be installed by pip.

Installation

• Install by using pip:
  The package is named ueberzug
• Packages of linux distributions:
  At least one packager applies patches to my code.
  So if there are issues uninstall it and install it via pip.
  Actually I think it's not fine that they call it ueberzug after changing the code.
  As bugs introduced by them look like they are part of my work.

Note: You can improve the performance of image manipulation functions by using pillow-simd instead of pillow.

Communication

The communication is realised via stdin.
A command is a request to execute a specific action with the passed arguments.
(Therefore a command has to contain a key value pair "action": action_name)
Commands are separated with a line break.

Command formats

• json: Command as json object
• simple:
  Key-value pairs seperated by a tab,
  pairs are also seperated by a tab
  ⚠️ ONLY FOR TESTING!
  Simple was never intended for the usage in production!
  It doesn't support paths containing tabs or line breaks
  which makes it error prone.
• bash: dump of an associative array (declare -p variable_name)

Actions

Add

Name: add
Description:
Adds an image to the screen.
If there's already an image with the same identifier
it will be replaced.

Key	Type	Description	Optional
identifier	String	a freely choosen identifier of the image	No
x	Integer	x position	No
y	Integer	y position	No
path	String	path to the image	No
width	Integer	desired width; original width will be used if not set	Yes
height	Integer	desired height; original width will be used if not set	Yes
max_width	Integer	Deprecated: replaced by scalers (this behavior is implemented by the default scaler contain) image will be resized (while keeping it's aspect ratio) if it's width is bigger than max width	Yes
max_height	Integer	Deprecated: replaced by scalers (this behavior is implemented by the default scaler contain) image will be resized (while keeping it's aspect ratio) if it's height is bigger than max height	Yes
draw	Boolean	redraw window after adding the image, default True	Yes
synchronously_draw	Boolean	redraw window immediately	Yes
scaler	String	name of the image scaler (algorithm which resizes the image to fit into the placement)	Yes
scaling_position_x	Float	the centered position, if possible Specified as factor of the image size, so it should be an element of [0, 1].	Yes
scaling_position_y	Float	analogous to scaling_position_x	Yes

ImageScalers:

Name	Description
crop	Crops out an area of the size of the placement size.
distort	Distorts the image to the placement size.
fit_contain	Resizes the image that either the width matches the maximum width or the height matches the maximum height while keeping the image ratio.
contain	Resizes the image to a size <= the placement size while keeping the image ratio.
forced_cover	Resizes the image to cover the entire area which should be filled while keeping the image ratio. If the image is smaller than the desired size it will be stretched to reach the desired size. If the ratio of the area differs from the image ratio the edges will be cut off.
cover	The same as forced_cover but images won't be stretched if they are smaller than the area which should be filled.

Remove

Name: remove
Description:
Removes an image from the screen.

Key	Type	Description	Optional
identifier	String	a previously used identifier	No
draw	Boolean	redraw window after removing the image, default True	Yes

Libraries

Just a reminder: This is a GPLv3 licensed project, so if you use any of these libraries you also need to license it with a GPLv3 compatible license.

Bash

The library is deprecated.
Dump associative arrays if you want to use ueberzug with bash.

First of all the library doesn't follow the posix standard,
so you can't use it in any other shell than bash.

Executing ueberzug library will print the path to the library to stdout.

Functions:

• ImageLayer starts the ueberzug process and uses bashs associative arrays to transfer commands.
• Also there will be a function named ImageLayer::{action_name} declared for each action.
  Each of this function takes the key values pairs of the respective action as arguments.
  Every argument of these functions has to be an associative key value pair.
  ImageLayer::{action_name} [{key0}]="{value0}" [{key1}]="{value1}" ...
  Executing such a function builds the desired command string according to the passed arguments and prints it to stdout.

Python

First of all everything which isn't mentioned here isn't safe to use and
won't necessarily shipped with new coming versions.

The library is included in ueberzug's package.

import ueberzug.lib.v0 as ueberzug

Classes:

1. Visibility:
   An enum which contains the visibility states of a placement.

   • VISIBLE
   • INVISIBLE

2. Placement:
   A placement to put images on.

   Every key value pair of the add action is an attribute (except identifier).
   Changing one of it will lead to building and transmitting an add command if the placement is visible.
   The identifier key value pair is implemented as a property and not changeable.

   Constructor:

   Name	Type	Optional	Description
   canvas	Canvas	No	the canvas where images should be drawn on
   identifier	String	No	a unique string used to address this placement
   visibility	Visibility	Yes	the initial visibility state (if it's VISIBLE every attribute without a default value needs to be set)
   **kwargs	dict	Yes	key value pairs of the add action

   Properties:

   Name	Type	Setter	Description
   identifier	String	No	the identifier of this placement
   canvas	Canvas	No	the canvas this placement belongs to
   visibility	Visibility	Yes	the visibility state of this placement - setting it to VISIBLE leads to the transmission of an add command - setting it to INVISIBLE leads to the transmission of a remove command

   Warning:
   The transmission of a command can lead to an IOError.
   (A transmission happens on assign a new value to an attribute of a visible Placement.
   The transmission is delayed till leaving a with-statement if lazy_drawing is used.)

3. ScalerOption:
   Enum which contains the useable scaler names.

4. Canvas:
   Should either be used with a with-statement or with a decorated function.
   (Starts and stops the ueberzug process)

   Constructor:

   Name	Type	default	Description
   debug	bool	False	suppresses printing stderr if it's false

   Methods:

   Name	Returns	Description
   create_placement	Placement	prevents the use of the same identifier multiple times, takes the same arguments as the Placement constructor (excluding canvas parameter)
   __call__	Function	Decorator which returns a function which calls the decorated function with the keyword parameter canvas=this_canvas_object. Of course other arguments are also passed through.
   request_transmission	-	Transmits queued commands if automatic_transmission is enabled or force=True is passed as keyword argument.

   Properties / Attributes:

   Name	Type	Setter	Description
   lazy_drawing	context manager factory	No	prevents the transmission of commands till the with-statement was left with canvas.lazy_drawing: pass
   synchronous_lazy_drawing	context manager factory	No	Does the same as lazy_drawing. Additionally forces the redrawing of the windows to happen immediately.
   automatic_transmission	bool	Yes	Transmit commands instantly on changing a placement. If it's disabled commands won't be transmitted till a lazy_drawing or synchronous_lazy_drawing with-statement was left or request_transmission(force=True) was called. Default: True

Examples

Command formats:

• Json command format: {"action": "add", "x": 0, "y": 0, "path": "/some/path/some_image.jpg"}
• Simple command format: action add x 0 y 0 path /some/path/some_image.jpg
• Bash command format: declare -A command=([path]="/some/path/some_image.jpg" [action]="add" [x]="0" [y]="0" )

Bash:

# process substitution example:
ueberzug layer --parser bash 0< <(
    declare -Ap add_command=([action]="add" [identifier]="example0" [x]="0" [y]="0" [path]="/some/path/some_image0.jpg")
    declare -Ap add_command=([action]="add" [identifier]="example1" [x]="10" [y]="0" [path]="/some/path/some_image1.jpg")
    sleep 5
    declare -Ap remove_command=([action]="remove" [identifier]="example0")
    sleep 5
)

# group commands example:
{
    declare -Ap add_command=([action]="add" [identifier]="example0" [x]="0" [y]="0" [path]="/some/path/some_image0.jpg")
    declare -Ap add_command=([action]="add" [identifier]="example1" [x]="10" [y]="0" [path]="/some/path/some_image1.jpg")
    read
    declare -Ap remove_command=([action]="remove" [identifier]="example0")
    read
} | ueberzug layer --parser bash

Python library:

• curses (based on https://docs.python.org/3/howto/curses.html#user-input):

  import curses
  import time
  from curses.textpad import Textbox, rectangle
  import ueberzug.lib.v0 as ueberzug
  
  
  @ueberzug.Canvas()
  def main(stdscr, canvas):
      demo = canvas.create_placement('demo', x=10, y=0)
      stdscr.addstr(0, 0, "Enter IM message: (hit Ctrl-G to send)")
  
      editwin = curses.newwin(5, 30, 3, 1)
      rectangle(stdscr, 2, 0, 2+5+1, 2+30+1)
      stdscr.refresh()
  
      box = Textbox(editwin)
  
      # Let the user edit until Ctrl-G is struck.
      box.edit()
  
      # Get resulting contents
      message = box.gather()
      demo.path = ''.join(message.split())
      demo.visibility = ueberzug.Visibility.VISIBLE
      time.sleep(2)
  
  
  if __name__ == '__main__':
      curses.wrapper(main)

• general example:

  import ueberzug.lib.v0 as ueberzug
  import time
  
  if __name__ == '__main__':
      with ueberzug.Canvas() as c:
          paths = ['/some/path/some_image.png', '/some/path/another_image.png']
          demo = c.create_placement('demo', x=0, y=0, scaler=ueberzug.ScalerOption.COVER.value)
          demo.path = paths[0]
          demo.visibility = ueberzug.Visibility.VISIBLE
  
          for i in range(30):
              with c.lazy_drawing:
                  demo.x = i * 3
                  demo.y = i * 3
                  demo.path = paths[i % 2]
              time.sleep(1/30)
  
          time.sleep(2)

Scripts:

• fzf with image preview: https://github.com/seebye/ueberzug/blob/master/examples/fzfimg.sh
• Mastodon viewer: https://github.com/seebye/ueberzug/blob/master/examples/mastodon.sh
• Fzf Mpd User Interface: https://github.com/seebye/fmui