SocketCanvas

SocketCanvas

Draw to an HTMLCanvas with WebSockets. SocketCanvas is a Go application that allows other applications speak WebSockets to draw to an HTMLCanvas.

Usage

You will need to Go installed to use SocketCanvas.

# using go install
go install codeberg.org/some/SocketCanvas@latest
~/go/bin/SocketCanvas

# cloning and building
git clone https://codeberg/some/SocketCanvas
cd SocketCanvas
go run main.go

Once running it will print

2025/08/21 20:56:30 Serving on port 8888

You can then open http://localhost:8888 in the browser.

Flags

-p int
      Port number (default 8888)
-stdin
      Enables listening for commands from stdin

Drawing

To draw to the canvas that is being served, you will need a WebSocket client to send draw commands. You can try it out with wscat if you have npm. Run npx wscat --connect ws://localhost:8888/draw. Note that the route is now /draw and using the ws protocol. Alternatively, you can run the application with the -stdin flag. Then you can send the following commands:

fill 0 0 0
rect 0 0 500 500
fill 250 250 250
circle 250 250 250

The resulting image:

Draw Commands

The draw commands follow this grammar

<DRAW COMMAND> = <COMMAND><ARGS>
<COMMAND> = fill | clear | rect |
            circle | line | shape |
            width | height | rotate |
            translate | push | pop | 
            stroke
<ARGS> = <ARG><ARGS>
<ARG> = int | float

An overview of implemented commands.

2025 © Somē Cho