Pixelflut

Fast pixelflut server written in C. It is a collaborative coding game. See https://cccgoe.de/wiki/Pixelflut for details about the game itself. In short: project the pixelflut server output onto a wall where many people can see it. Connected clients can then set single pixels by sending a string like "PX [x] [y] [color]\n" (e.g. "PX 100 300 00FF12\n") to its TCP socket. Use netcat, python or whatever you want.

Hardware requirements

Every x86 dual-core with a little bit of graphics power (for 2D SDL) should work. On an Core i3-4010U you can easily utilize a 1 GBit Nic. On large events, 10 GBit fiber and a few more CPU-Cores are even more fun. On real server hardware you want to add a graphics card. One thread per CPU-Core seems to be a good rule of thumb.

Features

Multithreaded
Can display an overlay with some statistics
Serves real-time WebGL histogram and help text to browsers (same TCP port)
Optional fade to black for old pixels to encourage pixel refreshes
Supported commands:
- send pixel: 'PX {x} {y} {GG or RRGGBB or RRGGBBAA as HEX}\n'
- set offset for future pixels: 'OFFSET {x} {y}\n'
- request pixel color: 'PX {x} {y}\n'
- request output resolution: 'SIZE\n'
- request client connection count: 'CONNECTIONS\n'
- request help message with all commands: 'HELP\n'

Build

On a clean Debian installation with the "SSH server" and "standard system utilities" selected during setup:

apt update
apt install xorg git build-essential pkg-config libsdl2-dev -y
git clone https://github.com/larsmm/pixelflut.git
cd pixelflut
make
./pixelflut --help

Connection limit

Best practise: set overall limit of the pixelflut-server high (--connections_max 1000) and limit max connections to the pixelflut port (default: 1234) per IP via iptables to 10-20:

nano iptables.save

paste (set limit in --connlimit-above):

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -p tcp -m tcp --dport 1234 --tcp-flags FIN,SYN,RST,ACK SYN -m connlimit --connlimit-above 20 --connlimit-mask 32 --connlimit-saddr -j REJECT
COMMIT

Ctrl+x, y, return to save. Activate:

iptables-restore < iptables.save

Start Server

start x server first, then the pixelflut server:

startx &  # start in background
./pixelflut

Stop Server

Press q or Ctrl+c

Multiple screens

If you need the output to be displayed on a second screen (projector), you have to tell it which display to use, e.g.:

DISPLAY=:0.1 ./pixelflut

If you expand the main display, the main display will be ":0.0" or ":0" and the projector ":0.1".
If you duplicate the main display, the main display will be ":0.0" and the projector ":1.0".
If you have only one display, it will be ":0.0" or ":0".

Display driver

Sometimes the free NVidia driver has problems on multiple displays. So install the proprietary driver:

detect the chip and find the right driver:

nano /etc/sources/sources.list

Add: "contrib non-free" after each source

apt install nvidia-detect
nvidia-detect

install driver:

apt install for example: nvidia-legacy-340xx-driver
reboot

configure your displays:

startx

run the following inside the x-session and setup your displays:

nvidia-settings

or via SSH:

DISPLAY=:0 nvidia-settings

maybe restart x server

Prevent standby

If you are using a notebook and want to close the lit. To disable all standby stuff:

systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target

TODO

Use epoll() to check multiple sockets for I/O events at once
better network-statistics

rphmeier/pixelflut