Chjixel

Chjixel is a simple multiplayer canvas. Players are anonymous and can place one pixel on a canvas with a fixed time delay.

How to run

• Run npm install
• Run NODE_ENV=production npm run build (alternatively, npm run watch)
• Copy and modify example.json5 to your taste
• Run NODE_ENV=production npm start <your config.json5>

API

Tokens

To enforce a timeout, each player session is identified by a token. A token is 16 alphanumeric characters, matching the regex [0-9a-zA-Z]{16}.

A certain number of tokens per IP address is allowed, by default 10, above which no new token will be accepted until at least one has its timer expire.

Index and color

Positions within the canvas are identified by their index. The index is simply the Y position, multiplied by the canvas width, and with the X position added.

The color palette has 27 colors, identified by 3-level RGB (values 0, 1, 2). The color index is produced with r * 9 + g * 3 + b * 1.

The 24-bit RGB values are taken by multiplying each component with 127 (this means the levels are 0, 127, 254 - note, not 255).

GET /canvas.png

Sends a PNG image of the entire canvas.

GET /b/dim

This endpoint returns a JSON object containing the canvas width and height inside its width and height attributes.

GET /b/events

/b/events is the server-sent events (SSE) endpoints used to receive real-time canvas updates. It takes two optional query string arguments: token, the token if the session listens for timer events on a token, and events, a negative mask of which events to not send.

The events sent are:

• canvas (except if events contains c) - Sent when the connection is established, contains a base64'd PNG of the entire canvas.
• place (except if events contains p) - Sent whenever a new pixel is placed. Contains a JSON object with the attributes i (the position index) and color (the color index).
• timer (only if token set, except if events contains t) - Sent when the connection is established and if the token has an outstanding timer, returns its current value in a JSON object with the attribute timer.
• ready (only if token set, except if events contains t) - Sent when the timer associated with the token expires.

PUT /b/place

/b/place is the endpoint used to place pixels. It takes as body a JSON object containing the attributes token, the token placing the pixel, i, the position index, and color, the color index.

The return status is 200 if it succeeded, in which case the body will be either an empty JSON object if no timeout is set in the config, or a JSON object with the timer attribute containing the timer value.

If a pixel of the same color already exists, the status is 409, with an empty JSON object.

If the token has an outstanding timer, the status is 429, with a JSON object containing the attribute timer with the outstanding timer value. If there is no timer attribute, then it means there are too many active tokens on the IP address.