Images from the Unity window lag by 1 step in versions >= 2.5.0

[mattdeitke]

When opening a controller and running:

from ai2thor.controller import Controller
c = Controller()
event = c.step('MoveAhead')

the Unity window that opens in the background is always 1-step behind the action!

However, when viewing the actual returned image from the event, it is up to date:

from PIL import Image
Image.fromarray(event.frame)

[mattdeitke]

This is expected behavior in versions >= 2.4.23!

For a bit of background, the servers that communicate between Python and Unity were updated, and this allows all actions to run substantially faster, which is often a preferred trade-off.

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But, it is of course useful to view and debug the current frame, so here are a few ways to do that:

1. Execute a dummy event, that will update the Unity window's frame:

c.step('Pass')

2. View the Event's image frame in a Python interactive environment with Python's Imaging Library (PIL):

# setup controller
from ai2thor.controller import Controller
c = Controller()
event = c.step('MoveAhead')

# visualize frame with PIL
from PIL import Image
Image.fromarray(event.frame)

3. Plot the image with matplotlib and have it open up in a new window (depending on your environment):

# setup controller
from ai2thor.controller import Controller
c = Controller()
event = c.step('MoveAhead')

# visualize frame with matplotlib
import matplotlib.pyplot as plt
plt.imshow(event.frame)
plt.axis('off')
plt.show()