selx

selx is a simple X11 rectangle selection tool, meant to be a smaller alternative to slop.

Some key features:

• Select a rectangle interactively.
• Select a window by right-click.
• Re-adjust the selection area by scroll-wheel up/down.
• Select a window by window ID.
• Adjustable selection line color and border width.

View the manpage for more details.

Preview

(Note: the preview image is using the old project name sx4 before it was renamed to selx)

Example Usage

• Take a screenshot of the selected area with sxot:

$ sxot -g "$(selx)" > out.ppm

• Recording the selected area with ffmpeg:

#!/bin/sh

IFS=, read x y w h << EOF
$(selx)
EOF
[ -z "$h" ] && exit 1  # nothing selected
# pad to an even resolution since some output format do no accept odd res
even_w="$(( w + (w % 2) ))"; even_h="$(( h + (h % 2) ))";

ffmpeg -f x11grab -s "${w}x${h}" -i ":0.0+$x,$y" -c:v libx264 -an \
	-framerate 30 -r 30 -threads "$(nproc)" -preset slow -tune zerolatency \
	-vf "format=yuv422p, pad=w=${even_w}:h=${even_h}" -crf 18 \
	"$HOME/videos/$(date '+%F_%T').mp4"

Dependencies

• Build Dependencies:

  • C99 compiler
  • Necessary library headers (on some distros you need to install *-dev packages to get header files)

• Runtime Dependencies:

  • X11 server
  • Xlib
  • libXrandr

Building

• Simple optimized build:

$ cc -o selx selx.c -O3 -s -l X11 -l Xrandr

The above command should also work with c99, gcc, clang or any other C compiler that has a POSIX compatible cli interface.

• Debug build with gcc (also works with clang):

$ gcc -o selx selx.c -std=c99 -Wall -Wextra -Wpedantic -Wshadow \
    -g3 -D DEBUG -O0 -fsanitize=address,undefined -l X11 -l Xrandr

• If you’re editing the code, you may optionally run some static analysis:

$ make -f etc/analyze.mk

Installing

Just copy the executable and the man-page to the appropriate location:

# cp selx /usr/local/bin
# cp selx.1 /usr/local/share/man/man1

Or using the install utility:

# install -Dm755 selx /usr/local/bin/selx
# install -Dm644 selx.1 /usr/local/share/man/man1/selx.1

A zsh completion script is also available for zsh users under etc/zsh-completion.