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Draw objects in the ARENA using Python!

Project description

ARENA Py - Python Examples

Draw objects in the ARENA using Python.

Install package using pip:

pip3 install arena-py

Hello ARENA

cd examples
python hello.py

(view results at https://xr.andrew.cmu.edu?scene=hello)

hello.py

import arena
arena.init("oz.andrew.cmu.edu", "realm", "hello")
arena.Object(arena.Shape.cube)
arena.handle_events()

arena.py library

The above is the simplest example of an ARENA Python program. This library sits above the ARENA pub/sub MQTT message protocol: JSON messages described in more detail at https://github.com/conix-center/ARENA-core which runs in a browser. That forms a layer, in turn, on top of A-Frame and THREE.js javascript libraries.

Here is a breakdown of the currently available arena.py functions

init

The init function takes 3 string positional arguments, and 2 optional arguments in order:

  • the DNS name of a pub/sub MQTT broker (currently Mosquitto v1.6.3, which runs the v3.1.1 protocol)
  • realm, currently the fixed string "realm" to indicate hierarchy level
  • scene name, a string
  • callback - a callback function to be called when ARENA network events are received. The function is passed a string argument, the network message, a JSON encoded string. (See below for more callback information)
  • port - a numerical port to connect if MQTT is running on a nonstandard port e.g. 3003 These are composed together to form an MQTT topic, in the example, "realm/s/hello". A successful init results in a connection with the MQTT server, ready to send and receive messages.

Object (create method)

Object takes multiple optional arguments and on success creates in the scene and returns a Python ARENA object. Accepted arguments are:

  • objName - Object name, a string. Object names should be unique within a scene
  • objType - an arena.objType enum from the set
    • cube
    • sphere
    • circle
    • cone
    • cylinder
    • dodecahedron
    • icosahedron
    • tetrahedron
    • octahedron
    • plane
    • ring
    • torus
    • torusKnot
    • triangle
    • gltf-model (see https://github.com/conix-center/ARENA-core#models for more details on GLTF format 3D models)
    • line
    • thickline
    • text
    • image
    • particle
    • light
  • location - a triple (x, y, z) coordinate in meters
  • rotation - a quad (x, y, z, w) rotation in quaternions
  • scale - a triple scaling factor in 3 dimensions
  • color - a triple RGB color where each component is in the range 0-255
  • persist - a boolean indicating whether to persist the created ARENA object to a database, such that it is visible when revisiting a scene. If False, the object will still be visible to everyone currently viewing the scene, but go away upon reload.
  • ttl - an integer for time to live, in seconds. objects will self-delete after this many seconds, and will not be persisted
  • parent - a string object name; sets this object to be one of possibly several children of the parent object with this objId
  • physics - an arena.Physics enum from
    • none - object remains fixed in place and does not interact with other physical objects
    • static - object remains fixed in place but DOES interact with other physical objects (collision, bounce off, etc.) Updates to the object's position can change it's location
    • dynamic - object roughly follows rough laws of gravity, and interacts with other physical objects. Updates to the object's position will not change it's location; it is under the control of physics engines, which are not consistent across multiple browsers viewing the scene
  • clickable - a boolean indicating whether the object has a click-listener component, allowing it to receive events from the arena.Event enum:
    • mousedown
    • mouseup
    • mouseenter
    • mouseleave
  • url - some objects use this parameter to refer to, e.g. a bitmap image, GLTF model, or web URL. See:
  • data - accepts arbitrary JSON data to specify additional attribute-value pairs not specified above to be added to the object's A-Frame entity; see A-Frame and ARENA-core documentation for more detail. An example of a somewhat fancy data message would look like
    data='{"impulse": {"on": "mouseup","force":"0 40 0","position":"10 1 1"},"material": {"color":"(0, 255, 0)", "transparent": false, "opacity": 1}}'

(this example adds an impulse component which fires on mouseup event, with a force of 40 in the Y direction, and sets the object color to green, and sets the object to be non-transparent)

Methods on Object

  • fireEvent takes 3 optional arguments
    • event - arena.Enum event to be sent to the object, e.g. mouseup, mousedown (default), mouseenter, mouseleave
    • position - a triple (x, y, z) where the event was fired in World coordinates (meters) default: (0, 0, 0)
    • source - an objName string indicating the object from which the event originated, default 'arenaLibrary'
  • update - takes multiple optional arguments to update values originally specified at object create time
    • location
    • rotation
    • scale
    • color
    • physics
    • data
    • clickable
  • delete - deletes the object from the scene

updateRig

takes 3 positional arguments

  • camera id for example "camera_er1k_er1k" if visiting ARENA URL with &fixedCamera=er1k
  • location - a triple (x, y, z) coordinate in meters
  • rotation - a quad (x, y, z, w) rotation in quaternions

handle_events

After synchronously drawing objects to the scene, it is necessary to start a loop to listen to and handle network events and call the callback function (specified at init() time)

flush_events

Empty out the buffer of sent/received network events; call this from main thread rather than sleep() or during loops.

callback

The data passed to the ARENA callback function is a JSON string best interpreted with json.loads() which turns it into a dictionary. These messages are the full contents of all MQTT messages pertaining to the scene, as specified in https://github.com/conix-center/ARENA-core. Most of them may not be of interest, and should be filtered to just events, with code like:

def callback(msg)
    jsonMsg = json.loads(msg)
    # filter non-event messages
    if jsonMsg["action"] != "clientEvent":
        return

    # look for only mousedown messages
    if jsonMsg["type"] != "mousedown":
        return

    # handle mousedown message, breaking out message data from the dict, e.g
    # jsonMsg["object_id"], jsonMsg[


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