cbdevnet / xelflut

Pretty fast server for multiplayer X11 canvas (pixelflut)

xelflut

A multiplayer X11 canvas.

Based on the idea of pixelflut, as seen at EasterHegg '14.

Written directly against XRender so it should probably be pretty fast.

Version numbers approximate π.

The name

It's funny on so many levels, some of which come only with an understanding of the german language and more-or-less (probably less) great math and programming humour.

Features

• IPv4 + IPv6 support
• Configurable frame rates and limits
• Configurable canvas dimensions
• Uniform or anisotropic scaling and centering
• Few dependencies / lightweight
• Slim codebase (~900 LoC)
• Alpha-transparency support

Building & Setup

Dependencies

• A C compiler
• (GNU) make
• libx11(-dev)
• libxrender(-dev)

Build process

Run make.

Setup

Configuration is done by passing arguments. Check the output of xelflut -h to see what is possible.

To install xelflut to the system (not in any way required), run make install.

Usage

Just run the resulting binary.

Run ./xelflut -h for some info on what you can do.

Within the window, press q to quit or c to clear the canvas.

By default, clients are limited to 50 pixels per frame (to change this, use the -l argument), 25 frames are rendered every second (configurable with -f). Clients exceeding the limits will be slowed down by default. This behaviour can be changed to one of the enforcement policies disconnect (Disconnect clients exceeding the limits), ignore (Ignore additional pixels until the next frame) or none (ignore the frame limit, keep other safeguards) with the -e <enforcer> option. Clients are allowed only one connection per host (though this can be circumvented by reasonably clever attackers). All limits and checks can be disabled (for example, for performance testing) by passing the -u option.

Protocol

Lines of ASCII text commands separated by \n via TCP on port 3141, unless you configure it differently (arguments -b and -p).

Send SIZE and the server responds with SIZE WIDTH HEIGHT

Send PX X Y RRGGBB or PX X Y RRGGBBAA to set a pixel to a hex color code.

There are some measures in place to limit the number of connections and pixels a client may have and set. Some are even configurable.

Bugs & Feedback

Please report bugs via the issue tracker.

If you use this on some kind of humungous screen or at a cool event, send me a picture ([email protected])!

xelflut's Issues

Check XRender support & version before using it

Should not pose a problem, but it would be the nice way of doing it.

overflow error, slow performance

Written directly against XRender so it should probably be pretty fast.

i detected the opposite while i expected the same...

when running via localhost i get overrun errors. i modified the code to ignore this state and the program works fine now. but it is incredible slow compared to the java version from https://github.com/defnull/pixelflut

what's wrong?

Store and only update the `fd_set` when required

Periodic screen shot functionality

Minimize calls to memmove

Analysis with callgrind shows that most instruction cycles are spent within memmove (copyback after data handling) and strtoul (pixel color parsing).

To limit the number of copyback operations performed, handle all buffer lines consecutively, then move at once.

Fix the window background

I think I'm missing an alpha value on the window background.

Can be seen when running a canvas smaller than the window.

Allow multiple listening sockets

• Introduce a type field to all socket descriptors
  • LISTEN
  • CLIENT
  • X11

Square pixels don't work yet

This is marked as TODO in the source code at

https://github.com/cbdevnet/xelflut/blob/master/x11.c#L205

Center/Scale mode

When configuring canvas dimensions smaller than the host display, allow scaling or centering the canvas

Exclusive sockets

Set IPV6_V6ONLY properly in the socket initialization