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Formatting PubSub Messages

For debugging purposes, or to create your own ARENA client software, it can be helpful to interact with ARENA’s PubSub messaging directly. Here we describe some examples of doing this.

Messaging Format Overview

All ARENA objects have similar well-defined schemas, and these are the basis for the over-the-wire message format shown below. This is the message format transmitted over the PubSub to create/update/delete objects. If you leave out required fields, defaults will be used.

  "object_id": "dinosaur",
  "persist": true,
  "type": "object",
  "action": "update",
  "data": {
    "object_type": "gltf-model",
    "url": "",
    "position": {
      "x": 0,
      "y": 1.7,
      "z": -5
    "rotation": {
      "x": 0,
      "y": 45,
      "z": 0
    "scale": {
      "x": 1,
      "y": 1,
      "z": 1
    "shadow": {
      "cast": true,
      "receive": true

Sample Publish/Subscribe

To run the commands below, you may need to install the ARENA Python client which includes these scripts.

Subscribe to Scene Object Messages

arena-py-sub -mh -s example

Publish a Scene Object Message

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_Earth", "action": "create", "type": "object", "data": {"object_type": "gltf-model", "position": {"x":0, "y": 0.1, "z": 0}, "url": "store/models/Earth.glb", "scale": {"x": 5, "y": 5, "z": 5}}}'

Sample scene: Earth and Moon with Markers

MQTT messages that define the scene:

Create models

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_Earth", "action": "create", "type": "object", "data": {"object_type": "gltf-model", "position": {"x":0, "y": 0.1, "z": 0}, "url": "store/models/Earth.glb", "scale": {"x": 5, "y": 5, "z": 5}}}'
arena-py-pub -mh -s example -m '{"object_id": "gltf-model_Moon", "action": "create", "type": "object", "data": {"parent": "gltf-model_Earth", "object_type": "gltf-model", "position": {"x":0, "y": 0.05, "z": 0.6}, "scale": {"x":0.05, "y": 0.05, "z": 0.05}, "url": "store/models/Moon.glb" }}'

Define animation and movement

arena-py-pub -mh -s example -m '{"object_id" : "gltf-model_Earth", "action": "update", "type": "object", "data": {"animation": { "property": "rotation", "to": "0 360 0", "loop": true, "dur": 20000, "easing": "linear"}} }'
arena-py-pub -mh -s example -m '{"object_id" : "gltf-model_Earth", "action": "update", "type": "object", "data": {"startEvents": "click", "property": "scale", "dur": 1000, "from": "10 10 10", "to": "5 5 5", "easing": "easeInOutCirc", "loop": 5, "dir": "alternate"} }'

Add a click-listener

arena-py-pub -mh -s example -m '{"object_id" : "gltf-model_Earth", "action": "update", "type": "object", "data": {"click-listener": ""}}'

Create marker objects

arena-py-pub -mh -s example -m '{"object_id" : "box0", "action": "create", "type": "object", "data": {"color": "blue", "object_type": "cube", "scale":  {"x": 0.2, "y": 0.2, "z": 0.2}, "position": {"x": 0, "y": 0, "z": 0} }}'
arena-py-pub -mh -s example -m '{"object_id" : "box1", "action": "create", "type": "object", "data": {"color": "red", "object_type": "cube", "scale":  {"x": 0.2, "y": 0.2, "z": 0.2}, "position": {"x": -0.7, "y": 1.67, "z": 2.11} }}'
arena-py-pub -mh -s example -m '{"object_id" : "box2", "action": "create", "type": "object", "data": {"color": "red", "object_type": "cube", "scale":  {"x": 0.2, "y": 0.2, "z": 0.2}, "position": {"x": -2.88, "y": 2.80, "z": -2.12} }}'
arena-py-pub -mh -s example -m '{"object_id" : "box3", "action": "create", "type": "object", "data": {"color": "red", "object_type": "cube", "scale":  {"x": 0.2, "y": 0.2, "z": 0.2}, "position": {"x": -0.09, "y": 1.30, "z": -3.66} }}'
arena-py-pub -mh -s example -m '{"object_id" : "box4", "action": "create", "type": "object", "data": {"color": "red", "object_type": "cube", "scale":  {"x": 0.2, "y": 0.2, "z": 0.2}, "position": {"x": 3.31, "y": 2.00, "z": -0.97} }}'

Messaging Format Reference

This is a reference list of primitives and how these can be created by interacting directly with ARENA’s PubSub.

Draw a Cube

Instantiate a cube and set all of it’s basic parameters.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 1, "y": 1, "z": -1}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 1, "y": 1, "z": 1}, "color": "#FF0000"}}'


Change only the color of the already-drawn cube.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": {"material": {"color": "#00FF00"}}}'


Say the cube has already been drawn. In a second command, this sets 50% transparency.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": {"material": {"transparent": true, "opacity": 0.5}}}'


Move the position of the already drawn cube.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": {"position": {"x": 2, "y": 2, "z": -1}}}'


Rotate the already drawn cube; these are in quaternions, not A-Frame degrees.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": {"rotation": {"x": 60, "y": 2, "z": 3}}}'

The quaternion (native) representation of rotation is a bit more tricky. The 4 parameters are X, Y, Z, W. Here are some simple examples:

  • 1, 0, 0, 0: rotate 180 degrees around X axis
  • 0, 0.7, 0, 0.7: rotate 90 degrees around Y axis
  • 0, 0, -0.7, 0.7: rotate -90 degrees around Z axis


Animate rotation of the already drawn cube.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": { "animation": { "property": "rotation", "to": "0 360 0", "loop": true, "dur": 10000}} }'

Other animations are available that resemble the "data": {"animation": { "property": ... }} blob above: see A-Frame Animation documentation for more examples.


Remove the cube.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "delete"}'


Create an image on the floor.

arena-py-pub -mh -s example -m '{"object_id": "image_floor", "action": "create", "type": "object", "data": {"object_type": "image", "position": {"x": 0, "y": 0, "z": 0.4}, "rotation": {"x": -0.7, "y": 0, "z": 0, "w": 0.7}, "url": "images/floor.png", "scale": {"x": 12, "y": 12, "z": 2}, "material": {"repeat": {"x": 4, "y": 4}}}}'

URLs work in the URL parameter slot. Instead of images/2.png it would be e.g. url( To update the image of a named image already in the scene, use this syntax.

arena-py-pub -mh -s example -m '{"object_id": "image_2", "action": "update", "type": "object", "data": {"material": {"src": ""}}}'

Images on Objects

Use the multisrc A-Frame Component to specify different bitmaps for sides of a cube or other primitive shape.

arena-py-pub -mh -s example -m '{"object_id": "die1", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 0, "y": 0.5, "z": -2}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 1, "y": 1, "z": 1}, "color": "#ffffff", "dynamic-body": {"type": "dynamic"}, "multisrc": {"srcspath": "images/dice/", "srcs": "side1.png, side2.png, side3.png, side4.png, side5.png, side6.png"}}}'

Other Primitives: TorusKnot

Instantiate a wacky torusKnot, then turn it blue. Other primitive types are available in the in A-Frame docs. Here is a brief list: box circle cone cylinder dodecahedron icosahedron tetrahedron octahedron plane ring sphere torus torusKnot triangle.

arena-py-pub -mh -s example -m '{"object_id": "torusKnot_1", "action": "create", "type": "object", "data": {"object_type": "torusKnot", "color": "red", "position": {"x": 0, "y": 1, "z": -4}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 1, "y": 1, "z": 1}}}'

arena-py-pub -mh -s example -m '{"object_id": "torusKnot_1", "action": "update", "type": "object", "data": {"material": {"color": "blue"}}}'


Instantiate a glTF v2.0 binary model (file extension .glb) from a URL.

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_1", "action": "create", "type": "object", "data": {"object_type": "gltf-model", "url": "", "position": {"x": 0, "y": 1, "z": -4}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 1, "y": 1, "z": 1}}}'

Animating GLTF Models

To animate a GLTF model (see GLTF Files for how to find animation names), and set the animation-mixer parameter.

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_3", "action": "update", "type": "object", "data": {"animation-mixer": {"clip": "*"}}}'

The asterisk means “play all animations”, and works better in some situations, where other times the name of a specific animation in the GLTF file works (or maybe several in sequence).

Relocalize Camera Rig

Move the camera rig (parent object of the camera) with ID camera_1234567890_er1k to a new coordinate (system). Values are x, y, z, (meters) x, y, z, w (quaternions).

arena-py-pub -mh -s example -m '{"object_id": "camera_1234567890_er1k", "action": "update", "type": "rig", "data": {"position": {"x": 1, "y": 1, "z": 1}, "rotation": {"x": 0.1, "y": 0, "z": 0, "w": 1} }}'

This assumes we know our camera ID was assigned as 1234567890. One way to find out your camera ID is, automatically assigned ones get printed on web browsers’ Developer Tools Console in a message like my-camera name camera_1234567890_X. That might not be easily knowable without snooping MQTT messages, so the &fixedCamera=er1k URL parameter lets us choose manually the unique ID. If used in the URL, the &name= parameter is ignored, and the derived camera/user ID is based on fixedCamera, so would be in this case camera_er1k_er1k

Move Camera

Move the camera with ID camera_1234567890_er1k to a new position. Values are x, y, z, (meters) x, y, z, w (quaternions). Action must be update.

arena-py-pub -mh -s example -m '{"object_id":"camera_1234567890_er1k","action":"update","type":"camera-override","data":{"object_type":"camera","position":{"x":1.692,"y":1.6,"z":4.371},"rotation":{"x":0.003,"y":-0.003,"z":0,"w":1}}}'

This assumes we know our camera ID. One way to find out your camera ID is, automatically assigned ones get printed on web browsers’ Developer Tools Console.

Camera Look At

Make the camera with ID camera_1234567890_er1k look at an object or coordinate. Target can be given as x, y, z coordinate object (e.g. {"x":1.692,"y":1.6,"z":4.371}), or as a string with an object ID (e.g. "cone_587431"). Action must be update.

arena-py-pub -mh -s example -m '{"object_id":"camera_1234567890_er1k","action":"update","type":"camera-override","data":{"object_type":"look-at","target":"cone_587431"}}'

arena-py-pub -mh -s example -m '{"object_id":"camera_1234567890_er1k","action":"update","type":"camera-override","data":{"object_type":"look-at","target":{"x": 0.467, "y": 2.066, "z": -1.027}}}'

This assumes we know our camera ID. One way to find out your camera ID is, automatically assigned ones get printed on web browsers’ Developer Tools Console.


Add some red text that says “Hello World”.

arena-py-pub -mh -s example -m '{"object_id": "text_3", "action": "create", "type": "object", "data": {"color": "red", "text": "Hello world!", "object_type": "text", "position": {"x": 0, "y": 3, "z": -4}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 1, "y": 1, "z": 1}}}'

Change text color properties A-Frame Text.

arena-py-pub -mh -s example -m '{"object_id": "text_3", "action": "update", "type": "object", "data": {"text": {"color": "green"}}}'


Create a red light in the scene.

arena-py-pub -mh -s example -m '{"object_id": "light_3", "action": "create", "type": "object", "data": {"object_type": "light", "position": {"x": 1, "y": 1, "z": 1}, "rotation": {"x": 0.25, "y": 0.25, "z": 0, "w": 1}, "color": "#FF0000"}}'

Default is ambient light. To change type, or other light A-Frame Light parameters, example: change to directional. Options: ambient, directional, hemisphere, point, spot.

arena-py-pub -mh -s example -m '{"object_id": "light_3", "action": "update", "type": "object", "data": {"light": {"type": "directional"}}}'


Play toy piano sound from a URL when you click a cube. Sets click-listener Component, waveform URL, and sound attribute.

arena-py-pub -mh -s example -m '{"object_id": "box_asharp", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 2.5, "y": 0.25, "z": -5}, "scale": {"x": 0.8, "y": 1, "z": 1}, "color": "#000000", "sound": {"src": "url(", "on": "mousedown"}, "click-listener": ""}}'

360 Video

Draw a sphere, set the texture src to be an equirectangular video, on the ‘back’ (inside).

arena-py-pub -mh -s example -m '{"object_id": "sphere_vid", "action": "create", "type": "object", "data": {"object_type": "sphere", "scale": {"x": 200, "y": 200, "z": 200}, "rotation": {"x": 0, "y": 0.7, "z": 0, "w": 0.7}, "color": "#808080", "material": {"src": "images/360falls.mp4", "side": "back"}}}'


Draw a purple line from (2, 2, 2) to (3, 3, 3).

arena-py-pub -mh -s example -m '{"object_id": "line_1", "action": "create", "type": "object", "data": {"object_type": "line", "start": {"x": 2, "y": 2, "z": 2}, "end": {"x": 3, "y": 3, "z": 3}, "color": "#CE00FF"}}'

Extend the line with a new segment, colored green.

arena-py-pub -mh -s example -m '{"object_id": "line_1", "action": "update", "type": "object", "data": {"line__2": {"start": {"x": 3, "y": 3, "z": 3}, "end": {"x": 4, "y": 4, "z": 4}, "color": "#00FF00"}}}'


A “thickline” (to improve openpose skeleton rendering visibility) - works like a line, but the lineWidth value specifies thickness, and multiple points can be specified at once, e.g. draw a pink line 11 pixels thick from 0, 0, 0 to 1, 0, 0 to 1, 1, 0 to 1, 1, 1. The shorthand syntax for coordinates is a bonus feature of lower level code; extending it for the rest of ARENA commands remains as an enhancement.

arena-py-pub -mh -s example -m '{"object_id": "thickline_8", "action": "create", "type": "object", "data": {"object_type": "thickline", "lineWidth": 11, "color": "#FF88EE", "path": "0 0 0, 1 0 0, 1 1 0, 1 1 1"}}'

You might be wondering, why can’t normal lines just use the scale value to specify thickness? But this one goes to eleven! Really though, normal lines perform faster. To update a “thickline” takes a special syntax because thicklines are really “meshline”s.

arena-py-pub -mh -s example -m '{"object_id": "thickline_8", "action": "update", "type": "object", "data": {"meshline": {"lineWidth": 11, "color": "#FFFFFF", "path": "0 0 0, 0 0 1"}}}'


Add the “click-listener” event to a scene object; click-listener is a Component defined in events.js. This works for adding other, arbitrary Components. A non-empty message gets sent to the Component’s init: function.

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "update", "type": "object", "data": {"click-listener": "enable"}}'

Persisted Objects

If we want our objects to return to the scene when we next open or reload our browser, we can commit them on creation to the ARENA Persistence DB by setting "persist": true.

arena-py-pub -mh -s example -m '{"object_id": "Ball2", "action": "create", "persist": true, "data": {"position": {"x": -1, "y": 1, "z": -1}, "color": "blue", "object_type": "sphere"}}'

Temporary Objects: TTL

It’s desirable to have objects that don’t last forever and pile up. For that there is the ‘ttl’ parameter that gives objects a lifetime, in seconds. This is an example usage for a sphere that disappears after 5 seconds.

arena-py-pub -mh -s example -m '{"object_id": "Ball2", "action": "create", "ttl": 5, "data": {"position": {"x": -1, "y": 1, "z": -1}, "color": "blue", "object_type": "sphere"}}'

Transparent Occlusion

To draw a shape that is transparent, but occludes other virtual objects behind it (to simulate virtual objects hidden by real world surfaces like a wall or table), include in the data section this JSON.

{"material": {"colorWrite": false}, "render-order": "0"}

…or a shortcut for the same occlusion, you can use…

{"material-extras": {"transparentOccluder": true}}

colorWrite is an attribute of the THREE.js Shader Material that, by exposing it, we make accessible like others belonging to the Material A-Frame Component, and is an alternative way of controlling visibility. render-order is a custom Component that controls which objects are drawn first (not necessarily the same as which are “in front of” others). All other ARENA objects are drawn with render-order of 1.

Background Themes

Adds one of many predefined backgrounds ( one of: none, default, contact, egypt, checkerboard, forest, goaland, yavapai, goldmine, threetowers, poison, arches, tron, japan, dream, volcano, starry, osiris) to the scene

arena-py-pub -mh -s example -m '{"object_id": "env", "action": "update", "type": "object", "data": {"environment": {"preset": "arches"}}}'


You can enable physics (gravity) for a scene object by adding the dynamic-body Component.

arena-py-pub -mh -s example -m '{"object_id": "box_3", "action": "update", "type": "object", "data": {"dynamic-body": {"type": "dynamic"}}}'

One physics feature is applying an impulse to an object to set it in motion. This happens in conjunction with an event. As an example, here are messages setting objects fallBox and fallBox2 to respond to mouseup and mousedown messages with an impulse with a certain force and position.

arena-py-pub -mh -s example -m '{"object_id": "fallBox2", "action": "create", "type": "object", "data": {"object_type": "cube", "dynamic-body": {"type": "dynamic"}, "impulse": {"on": "mousedown", "force": "1 50 1", "position": "1 1 1"}, "click-listener": "", "position": {"x": 0.1, "y": 4.5, "z": -4}, "scale": {"x": 0.5, "y": 0.5, "z": 0.5}}}'

arena-py-pub -mh -s example -m '{"object_id": "fallBox", "action": "create", "type": "object", "data": {"object_type": "cube", "dynamic-body": {"type": "dynamic"}, "impulse": {"on": "mouseup", "force": "1 50 1", "position": "1 1 1"}, "click-listener": "", "position": {"x": 0, "y": 4, "z": -4}, "scale": {"x": 0.5, "y": 0.5, "z": 0.5}}}'

Parent/Child Linking

There is support to attach a child to an already-existing parent scene objects. When creating a child object, set the "parent": "parent_object_id" value in the JSON data. For example if parent object is gltf-model_Earth and child object is gltf-model_Moon, the commands would look like:

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_Earth", "action": "create", "type": "object", "data": {"object_type": "gltf-model", "position": {"x": 0, "y": 0.1, "z": 0}, "url": "store/models/Earth.glb", "scale": {"x": 5, "y": 5, "z": 5}}}'

arena-py-pub -mh -s example -m '{"object_id": "gltf-model_Moon", "action": "create", "type": "object", "data": {"parent": "gltf-model_Earth", "object_type": "gltf-model", "position": {"x": 0, "y": 0.05, "z": 0.6}, "scale": {"x": 0.05, "y": 0.05, "z": 0.05}, "url": "store/models/Moon.glb" }}'

Child objects inherit attributes of their parent, for example scale. Scale the parent, the child scales with it. If the parent is already scaled, the child scale will be reflected right away. Child position values are relative to the parent and also scaled.

Goto URL

Navigates to entirely new page into browser when clicked, or other event (requires click-listener).

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 1, "y": 1, "z": -1}, "click-listener": "", "goto-url": { "dest": "newtab", "on": "mousedown", "url": "http:"}}}'


Creates a landmark that can be teleported to from the UI list, or is one of the random starting positions for the scene

arena-py-pub -mh -s example -m '{"object_id": "cube_1", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 1, "y": 1, "z": -1}, "landmark": { "label": "Cube 1", "randomRadiusMin": 1, "randomRadiusMax": 2, "lookAtLandmark": true }}}'


Particles are based on aframe-spe-particles-component, javascript loaded from aframe-spe-particles-component.min.js.

For now, it’s not directly supported, but rather by passing JSON inside the data{} element. The syntax for parameter names has been updated so instead of a name like this that is space-separated it becomes spaceSeparated (camel case). Three examples here have been created starting with the examples in aframe-spe-particles-component examples then reformulating to ARENA JSON syntax.

arena-py-pub -mh -s example -m '{"object_id": "smoke", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 0, "y": 1, "z": -3.9}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 0.01, "y": 0.01, "z": 0.01}, "color": "#ffffff", "spe-particles": {"texture": "textures/fog.png", "velocity": "1 30 0", "velocitySpread": "2 1 0.2", "particleCount": 50, "maxAge": 4, "size": "3, 8", "opacity": "0, 1, 0", "color": "#aaa, #222"}}}'

arena-py-pub -mh -s example -m '{"object_id": "flames", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 0, "y": 1, "z": -3.8}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 0.01, "y": 0.01, "z": 0.01}, "color": "#ffffff", "spe-particles": {"texture": "textures/explosion_sheet.png", "textureFrames": "5 5", "velocity": "4 100 0", "acceleration": "0 10 0", "accelerationSpread": "0 10 0", "velocitySpread": "4 0 4", "particleCount": 15, "maxAge": 1, "size": "4, 8", "sizeSpread": 2, "opacity": "1, 0", "wiggle": "0 1 0", "blending": "additive"}}}'

arena-py-pub -mh -s example -m '{"object_id": "sparks", "action": "create", "type": "object", "data": {"object_type": "cube", "position": {"x": 0, "y": 1, "z": -4}, "rotation": {"x": 0, "y": 0, "z": 0, "w": 1}, "scale": {"x": 0.01, "y": 0.01, "z": 0.01}, "color": "#ffffff", "spe-particles": {"texture": "textures/square.png", "color": "yellow, red", "particleCount": 3, "maxAge": 0.5, "maxAgeSpread": 1, "velocity": "40 200 40", "velocitySpread": "10 3 10", "wiggle": "50 0 50", "wiggleSpread": "15 0 15", "emitterScale": 8, "sizeSpread": 10, "randomizeVelocity": true}}}'

Particles are very complicated and take a lot of parameters. It would not make sense to translate all of them into explicit ARENA types, thus this flexible ‘raw JSON’ format is used.


Click events are generated as part of the laser-controls A-Frame entity; you get the events if you click the lasers on scene entities that have click-listener Component in their HTML declaration (see index.html), or have later had click-listener enabled via an MQTT message (see above). Mouse events occur if you click in a browser, or tap on a touchscreen as well.

  • mouseenter
  • mouseleave
  • mousedown
  • mouseup
  • triggerdown / triggerup for left and right hand controllers

The MQTT topic name for viewing these events can be the standard prefix (e.g. realm/s//example/) ending with a string made up of object ID that generated the event. An example event MQTT:

arena-py-pub -mh -s example -m '{"object_id": "fallBox2", "action": "clientEvent", "type": "mousedown", "data": {"position": {"x": -0.993, "y": 0.342, "z": -1.797}, "source": "camera_8715_er"}}'

Full list of Vive controller event names:

  • triggerdown
  • triggerup
  • gripdown
  • gripup
  • menudown
  • menuup
  • systemdown
  • systemup
  • trackpaddown
  • trackpadup

Scene Settings

Some settings are available by setting attributes of the Scene element (see A-Frame Scene) for example, turn on statistics:

arena-py-pub -mh -s example -m '{"object_id": "scene", "action": "update", "type": "object", "data": {"stats": true}}'

Customize the fog (notice 3 character hexadecimal color representation):

arena-py-pub -mh -s example -m '{"object_id": "scene", "action": "update", "type": "object", "data": {"fog": {"type": "linear", "color": "#F00"}}}'

Remove the “enter VR” icon:

arena-py-pub -mh -s example -m '{"object_id": "scene", "action": "update", "type": "object", "data": {"vr-mode-ui": {"enabled": false}}}'