ARENA Library Scene Callbacks

Library supported callback functions.

Scene callbacks

on_msg_callback

This is called whenever there is a new message sent to the client. Use this whenever you want to sniff out all incoming messages.

Usage:

# [scene] is the Scene that called the callback
# [obj] will be an Object instance
# [msg] is the raw JSON message as a dict
def on_msg_callback(scene, obj, msg):
    ## do stuff with obj here
    obj.object_id
    obj.data.position.x
    obj.data.scale.y
    # etc.
    # could also do obj["object_id"] or msg["object_id"]

scene.on_msg_callback = on_msg_callback

new_obj_callback

This is called whenever there is a new object that has been created in the scene, one that the user does not have a reference to. Use this to make references to any new objects that may appear during a programs lifetime. Also a good way to find camera ID’s.

Usage:

# [scene] is the Scene that called the callback
# [obj] will be an Object instance
# [msg] is the raw JSON message as a dict
def new_obj_callback(scene, obj, msg):
    ## do stuff with obj here
    obj.object_id
    obj.data.position.x
    obj.data.scale.y
    # etc.
    # could also do obj["object_id"] or msg["object_id"]

scene.new_obj_callback = new_obj_callback

delete_obj_callback

This is called whenever there is an object has been deleted in the scene. arena-py will look for all “action” = “delete” messages and call this callback. Use this to delete references and to be notified when an object is removed by another user or program.

Usage:

# [scene] is the Scene that called the callback
# [obj] will be an Object instance
# [msg] is the raw JSON message as a dict
def delete_obj_callback(scene, obj, msg):
    ## do stuff with obj here
    obj.object_id
    obj.data.position.x
    obj.data.scale.y
    # etc.
    # could also do obj["object_id"] or msg["object_id"]

scene.delete_obj_callback = delete_obj_callback

User callbacks

user_join_callback

This is called whenever the library detects/finds a new user that it hasn’t seen before in a scene. Note: this is not neccesarily called when a user “joins” a scene, rather, it is called when the library first sees a Camera object/receives an “update” message from a user.

Usage:

def user_join_callback(camera):
    ## Get access to user state
    # camera is a Camera class instance (see Objects)
    camera.object_id
    camera.displayName
    camera.hasVideo
    camera.displayName
    # etc.

scene.user_join_callback = user_join_callback

user_left_callback

This is called whenever a user leaves a scene/sends a delete message.

Usage:

def user_left_callback(camera):
    ## Get access to user state
    # camera is a Camera class instance (see Objects)
    camera.object_id
    camera.displayName
    camera.hasVideo
    camera.displayName
    # etc.

scene.user_left_callback = user_left_callback

Adding callbacks when you instantiate the class

You can also add callbacks like so:

from arena import *

def on_msg_callback(scene, obj, msg):
    pass

def new_obj_callback(scene, obj, msg):
    pass

def delete_obj_callback(scene, obj, msg):
    pass

scene = Scene(..., on_msg_callback=on_msg_callback, new_obj_callback=new_obj_callback, delete_obj_callback=delete_obj_callback)

Custom Message Callbacks

If you need to use an MQTT client, the Scene object exposes a way to use its MQTT client to subscribe to custom topics.

def led_toggle(client, userdata, msg):
    # do stuff here

scene.message_callback_add("custom/control/light", led_toggle)