I was frustrated by the low amount of standalone lightweight compositors. Compton was forked from Dana Jansens' fork of xcompmgr and refactored. I fixed whatever bug I found, and added features I wanted. Things seem stable, but don't quote me on it. I will most likely be actively working on this until I get the features I want. This is also a learning experience for me. That is, I'm partially doing this out of a desire to learn Xlib.

Changes from xcompmgr:

inactive window transparency (specified with -i)
titlebar/frame transparency (specified with -e)
menu transparency (thanks to Dana)
shadows are now enabled for argb windows, e.g. terminals with transparency
removed serverside shadows (and simple compositing) to clean the code, the only option that remains is clientside shadows
configuration files (specified with --config)
colored shadows (with --shadow-[red/green/blue] value)
a new fade system
vsync (still under development)
several more options

Fixes from the original xcompmgr:

fixed a segfault when opening certain window types
fixed a memory leak caused by not freeing up shadows (from the freedesktop repo)
fixed the conflict with chromium and similar windows
many more

Building

Dependencies:

B for build-time

R for runtime

libx11 (B,R)
libxcomposite (B,R)
libxdamage (B,R)
libxfixes (B,R)
libXext (B,R)
libxrender (B,R)
pkg-config (B)
make (B)
xproto / x11proto (B)
bash (R)
xprop,xwininfo / x11-utils (R)
libpcre (B,R) (Will probably be made optional soon)
libconfig (B,R) (Will probably be made optional soon)

To build, make sure you have the above dependencies:

$ make
$ make install

Example Usage

$ compton -cC -i 0.6 -e 0.6 -f
$ compton --config ~/compton.conf

Options and Configuration

compton [-d display] [-r radius] [-o opacity]
        [-l left-offset] [-t top-offset]
        [-i opacity] [-e opacity] [-cCfFSdG]
        [--config path] [--shadow-red value]
        [--shadow-green value] [--shadow-blue value]
        [--inactive-opacity-override] [--inactive-dim value]
        [--mark-wmwin-focused] [--shadow-exclude condition]
        [--mark-ovredir-focused] [--no-fading-openclose]
        [--shadow-ignore-shaped] [--detect-round-corners]

-d display: Which display should be managed.
-r radius: The blur radius for shadows. (default 12)
-o opacity: The translucency for shadows. (default .75)
-l left-offset: The left offset for shadows. (default -15)
-t top-offset: The top offset for shadows. (default -15)
-I fade-in-step: Opacity change between steps while fading in. (default 0.028)
-O fade-out-step: Opacity change between steps while fading out. (default 0.03)
-D fade-delta-time: The time between steps in a fade in milliseconds. (default 10)
-m opacity: The opacity for menus. (default 1.0)
-c: Enabled client-side shadows on windows.
-C: Avoid drawing shadows on dock/panel windows.
-z: Zero the part of the shadow's mask behind the window (experimental).
-f: Fade windows in/out when opening/closing and when opacity changes, unless --no-fading-openclose is used.
-F: Equals -f. Deprecated.
-i opacity: Opacity of inactive windows. (0.1 - 1.0)
-e opacity: Opacity of window titlebars and borders. (0.1 - 1.0)
-G: Don't draw shadows on DND windows
-b: Daemonize/background process.
-S: Enable synchronous operation (for debugging).
--config path: Look for configuration file at the path.
--shadow-red value: Red color value of shadow (0.0 - 1.0, defaults to 0).
--shadow-green value: Green color value of shadow (0.0 - 1.0, defaults to 0).
--shadow-blue value: Blue color value of shadow (0.0 - 1.0, defaults to 0).
--inactive-opacity-override: Inactive opacity set by -i overrides value of _NET_WM_OPACITY.
--inactive-dim value: Dim inactive windows. (0.0 - 1.0, defaults to 0)
--mark-wmwin-focused: Try to detect WM windows and mark them as active.
--shadow-exclude condition: Exclude conditions for shadows.
--mark-ovredir-focused: Mark over-redirect windows as active.
--no-fading-openclose: Do not fade on window open/close.
--shadow-ignore-shaped: Do not paint shadows on shaped windows.
--detect-rounded-corners: Try to detect windows with rounded corners and don't consider them shaped windows.

Format of a condition:

condition = <target>:<type>[<flags>]:<pattern>

<target> is one of "n" (window name), "i" (window class instance), and "g" (window general class)

<type> is one of "e" (exact match), "a" (match anywhere), "s" (match from start), "w" (wildcard), and "p" (PCRE regular expressions, if compiled with the support).

<flags> could be a series of flags. Currently the only defined flag is "i" (ignore case).

<pattern> is the actual pattern string.

Configuration

A more robust sample configuration file is available in the repository.

Example

~/compton.conf:

# Shadows
shadow = true;

# Opacity
inactive-opacity = 0.8;
frame-opacity = 0.7;

# Fades
fading = true;

Run with:

$ compton --config ~/compton.conf

License

Although compton has kind of taken on a life of its own, it was originally an xcompmgr fork. xcompmgr has gotten around. As far as I can tell, the lineage for this particular tree is something like:

Keith Packard (original author)
Matthew Hawn
...
Dana Jansens
chjj and richardgv

Not counting the tens of people who forked it in between.

See LICENSE for more info.