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The OutputDataWriter add-on

The OutputDataWriter add-on will write the raw list of bytes returned by the build to disk per communicate() call. This is best used as a debugging tool.

The raw response is usually written as resp in our example controllers:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils

c = Controller()
resp = c.communicate([TDWUtils.create_empty_room(12, 12),
                      Controller.get_add_object(model_name="vase_02",
                                                object_id=0),
                      {"$type": "send_transforms",
                       "frequency": "once"}])
print(resp)
c.communicate({"$type": "terminate"})

Output:

[b'\x14\x00\x00\x00tran\x0c\x00\x14\x00\x04\x00\x08\x00\x0c\x00\x10\x00\x0c\x00\x00\x00D\x00\x00\x000\x00\x00\x00\x18\x00\x00\x00\x04\x00\x00\x00\x03\x00\x00\x00\xc6a\xcd6GUJ\xb8\x00\x00\x80?\x04\x00\x00\x00aU\xca7A[M6\x81\xfd\x837\x00\x00\x80?\x03\x00\x00\x00\x00J\x995\x00_\xf49\xa8t\xac\xb6\x01\x00\x00\x00\x00\x00\x00\x00', b'\x00\x00\x00\x02']

If we add an OutputDataWriter, on every frame each bytes object in resp will be encoded to a base64 string, then the list will be serialized to a string using JSON, and then the string will be saved to a file:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.output_data_writer import OutputDataWriter
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH

output_directory = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("output_data_writer")
print(f"Output will be saved to: {output_directory}")
c = Controller()
writer = OutputDataWriter(output_directory=output_directory)
c.add_ons.append(writer)
c.communicate([TDWUtils.create_empty_room(12, 12),
               Controller.get_add_object(model_name="vase_02",
                                         object_id=0),
               {"$type": "send_transforms",
                "frequency": "once"}])
c.communicate({"$type": "terminate"})
# Open the file and read the text.
path = output_directory.joinpath("00000000.txt")
print(path.read_text())

Output:

["FAAAAHRyYW4MABQABAAIAAwAEAAMAAAARAAAADAAAAAYAAAABAAAAAMAAADGYc02R1VKuAAAgD8EAAAAYVXKN0FbTTaB/YM3AACAPwMAAAAASpk1AF/0Oah0rLYBAAAAAAAAAA==", "AAAAAg=="]

Read and deserialize saved data

Deserialize data by calling read(path) or read(value):

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.output_data_writer import OutputDataWriter
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH

output_directory = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("output_data_writer")
print(f"Output will be saved to: {output_directory}")
c = Controller()
writer = OutputDataWriter(output_directory=output_directory)
c.add_ons.append(writer)
c.communicate([TDWUtils.create_empty_room(12, 12),
               Controller.get_add_object(model_name="vase_02",
                                         object_id=0),
               {"$type": "send_transforms",
                "frequency": "once"}])
c.communicate({"$type": "terminate"})
# Open the file and read the text.
path = output_directory.joinpath("00000000.txt")
data = writer.read(path)
print(data)

Output:

[b'\x14\x00\x00\x00tran\x0c\x00\x14\x00\x04\x00\x08\x00\x0c\x00\x10\x00\x0c\x00\x00\x00D\x00\x00\x000\x00\x00\x00\x18\x00\x00\x00\x04\x00\x00\x00\x03\x00\x00\x00\xc6a\xcd6GUJ\xb8\x00\x00\x80?\x04\x00\x00\x00aU\xca7A[M6\x81\xfd\x837\x00\x00\x80?\x03\x00\x00\x00\x00J\x995\x00_\xf49\xa8t\xac\xb6\x01\x00\x00\x00\x00\x00\x00\x00', b'\x00\x00\x00\x02']

This output matches the output of the first example, when we printed resp.

The path parameter can be a string (a file path), a Path (also a file path), or an integer representing the frame count:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.output_data_writer import OutputDataWriter
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH

output_directory = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("output_data_writer")
print(f"Output will be saved to: {output_directory}")
c = Controller()
writer = OutputDataWriter(output_directory=output_directory)
c.add_ons.append(writer)
c.communicate([TDWUtils.create_empty_room(12, 12),
               Controller.get_add_object(model_name="vase_02",
                                         object_id=0),
               {"$type": "send_transforms",
                "frequency": "once"}])
c.communicate({"$type": "terminate"})
# Corresponds to: 00000000.txt
data = writer.read(0)
print(data)

When to use OutputDataWriter

OutputDataWriter is best used as a debugging tool. It was created to debug JsonWriter quickly and without a controller; in this case, a controller script wrote out some output data and then JsonWriter used that data to "reset" some add-ons repeatedly as part of a test.

When to not use OutputDataWriter

  • OutputDataWriter is usually not significantly faster than parsing the raw bytes into output data objects and then serializing those. This is because it encodes to base64 before writing. Especially in the case of images, OutputDataWriter is probably not what you want to use.
  • OutputDataWriter can't be used to reset scene states. It can be used to "reset" add-ons like this:
from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.output_data_writer import OutputDataWriter
from tdw.add_ons.object_manager import ObjectManager
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH

"""
Write raw output data per frame from the build.
"""

path = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("resp_saver")
print(f"Output data will be saved to: {path}")
c = Controller()
# Add an ObjectManager, which will start requesting output data.
object_manager = ObjectManager()
# Add an OutputDataWriter.
writer = OutputDataWriter(output_directory=path)
c.add_ons.extend([object_manager, writer])
# Get an object ID
object_id = 0
# Load the scene.
commands = [TDWUtils.create_empty_room(12, 12)]
commands.extend(Controller.get_add_physics_object(model_name="vase_02",
                                                  object_id=object_id,
                                                  position={"x": 0, "y": 5, "z": 0}))
# Frame 0: Send the commands.
c.communicate(commands)
# Print the position of the object.
print("Frame 0:", object_manager.transforms[object_id].position[1])
# Frame 1: End the simulation.
c.communicate({"$type": "terminate"})
# Print the position of the object.
print("Frame 1:", object_manager.transforms[object_id].position[1])
# Load the saved data.
print("Reading saved data...")
frame_0 = writer.read(0)
frame_1 = writer.read(1)
# Create a new ObjectManager and set `initialized` to True because we don't need to send initialization commands.
object_manager = ObjectManager()
object_manager.initialized = True
# Call `on_send(frame_0) to reproduce the data at frame 0.
object_manager.on_send(resp=frame_0)
# Print the position of the object.
print("Frame 0:", object_manager.transforms[object_id].position[1])
# Call `on_send(frame_1) to reproduce the data at frame 1.
object_manager.on_send(resp=frame_1)
# Print the position of the object.
print("Frame 1:", object_manager.transforms[object_id].position[1])

Output:

Frame 0: 4.999019
Frame 1: 4.997057
Reading saved data...
Frame 0: 4.999019
Frame 1: 4.997057

While this can be useful (again, it's probably most useful as a debug tool), this doesn't actually set the positions and rotations of objects in the scene; it merely sets what the ObjectManager thinks the positions and rotations are.

Next: Create a custom data writer

Return to the README

Example controllers:

Python API: