Meet SimPixel

I have someone I’d like you to meet. SimPixel, meet everyone. Everyone, SimPixel.

# SimPixel, introduce yourself

SimPixel is a WebGL visualizer for LED displays, very much like the ones Adam and Dan build over at Maniacal Labs.

some Maniacal Labs LED projects

Very much alike. In fact, it’s probably so much like their displays because I built most of SimPixel while sitting at Adam’s workbench. I don’t know, there could be a connection. If you too would like to take a seat at Adam’s illustrious workbench someday, hack away. You can also try the fullscreen demo.

BiblioPixel, ML’s light animation library, sends layouts and colors to SimPixel using a simple WebSocket protocol.

# The Protocol

By itself, SimPixel is useless. To turn on the lights, it connects to a WebSocket service. That service is expected to send certain messages, namely a configuration message followed by a series of color messages.

# Configuration message

The configuration message conveys the spatial layout of the LEDs.

For example, a configuration message of 0x0000009A02FE000C is interpreted as follows.


The leading 0x0000 opcode identifies this as a configuration (ie, setup) message, followed by a series of 16-bit signed integers which indicate the 3D coordinates of each LED, of the form: X1,Y1,Z1,X2,Y2,Z2, …, Xn,Yn,Zn

# Color message

The color message(s) specify what color each LED should be at the current moment in time.

An example color message, 0x0001 40 D6 7F, breaks down to:


The leading 0x0001 opcode identifies this as a color message, followed by a series of 8-bit unsigned integers which indicate the RGB colors of each LED, of the form: R1,G1,B1,R2,G2,B2, …, Rn,Gn,Bn

For a concise reference, see

# The Ghost in the Recording

The live demo at the top of this post isn’t connected to any WebSocket service. Instead, it’s using a recording apparatus that I cobbled together. I pushed a configuration frame and a bunch of color frames into an array, converted their ArrayBuffers into base64 strings, and saved those into a quite large JSON recording file.

I only mention it to lead up to the following. While editing the recording JSON file, I zoomed out a little and something caught my eye. I zoomed out more and a pattern took shape.

Here’s a screenshot of the JSON file in my terminal, zoomed out as far as it’ll go.

image of base64-encoded recording

The waves of red, green, and blue is evident even in this doubly-encoded format. Pretty cool.