exposed unity random seed to python api surface

[sagadre]

Main change is on L3057 in BaseFPSAgentController.cs

[mattdeitke]

To add to some context, I much prefer this solution, of setting the random seed globally, rather than every random action including a random seed, which then sets the seed inside of the action.

So, instead of:

controller.step(action="RandomizeMaterials", randomSeed=42)
controller.step(action="RandomizeMaterials", randomSeed=42)

you have

controller.step(action="SetRandomSeed", seed=42)
controller.step(action="RandomizeMaterials")
controller.step(action="RandomizeMaterials")

This is much more consistent with how one expects to use a random seed in other libraries. For instance, in NumPy, one doesn't use:

np.random.randn((125, 125), random_seed=42)
np.random.randn((125, 125), random_seed=45)
np.random.randn((125, 125), random_seed=46)

You instead set the seed once globally and keep sampling from it.

[mattdeitke]

LGTM.

Added a test for it, and visually tested in Colab: https://colab.research.google.com/drive/1QjMJrlXKS-b_o1N2MMbcf_0oTGdaaYCi?usp=sharing

[sagadre]

Thanks Matt, I like your suggestion!

In the interim, one thing to note is the following sequences of actions will set the random seed twice.

controller.step(action="SetRandomSeed", seed=42)
controller.step(action="InitialRandomSpawn") # default randomSeed=0, so the previous line didn't really do anything

However, this case should not really cause issues for the end user (behavior should still be reproducible even though the seed switches).

[sagadre]

Another thing to consider is adding a random seed param to the Controller constructor and to reset so someone could set the seed from there and then not worry about having to call SetRandomSeed. Would still be useful to have this function for some use cases.

[mattdeitke]

Another thing to consider is adding a random seed param to the Controller constructor and to reset so someone could set the seed from there and then not worry about having to call SetRandomSeed. Would still be useful to have this function for some use cases.

I tend to prefer against having a seed in reset/initialize. Some reasons:

1. Supporting 2 ways to do something (i.e., setting a random seed as an action or upon initialization) is a bit dangerous. If one reads the documentation, and sees that there's a seed parameter upon initialize, it doesn't seem likely that one would also expect it to be a standalone action, and vice-versa. The idea of having 2 ways to do something is also unpythonic.
2. One common use case that can only be supported with the action is the ability to call reset right before some random action, so as to reset the seed when that action is reached. For instance:

import random

controller.step(action="SetRandomSeed", seed=42)
controller.step(action="RandomizeMaterials")

# --- some code that may utilize unity's random function, but the scene has not reset ---
random_n_steps = random.choice(range(5, 20))
for _ in range(random_n_steps):
     # assume this is a stochastic movement that randomly samples moveMagnitude in Unity
    controller.step(action="MoveAhead")

controller.step(action="SetRandomSeed", seed=42)
controller.step(action="RandomizeLighting")

If one only knew about SetRandomSeed in reset, then one would not be able to guarantee that the random numbers generated for the RandomizeLighting action were reproducible, since the seed set upon reset would be sampled from an nondeterministic amount of times.

3. Initialization is super large right now. Between all agent types, it is probably the hardest thing to maintain because it is so messy with so many existing parameters.
4. Using actionFinishedEmit is extremely fast since it can largely cache the previously returned Event (without having to pass back new object metadata or image frames). Thus, keeping SetRandomSeed as a standalone action incurs a largely negligible performance cost.

[sagadre]

oops this case could be an issue with the current codebase

controller.step(action="SetRandomSeed", seed=42)
e1 = controller.step(action="InitialRandomSpawn") # default randomSeed=0, so the previous line didn't really do anything
controller.step(action="SetRandomSeed", seed=41)
e2 = controller.step(action="InitialRandomSpawn")

A user might expect e1 != e2 but this is not the case. Would not be an issue for RandomizeMaterials etc. tho.

[mattdeitke]

I think this is more of a fault of InitialRandomSpawn, which is getting deprecated soon, having a randomSeed parameter, rather than it being a fault of the current setup.

[ekolve]

I am fine with the change with one caveat that we need to ensure that we make users aware that the order that actions are executed in will change the result if the actions invoke the RNG. For example,

SetRandomSeed
RandomizeMaterials
RandomizeMaterials

vs

SetRandomSeed
RandomizeMaterials
SomeOtherRandomAction
RandomizeMaterials

The latter will result in a different set of random materials. This behavior is not different from say using Python's random and explicitly setting the seed. There is also the issue of an action on the Unity side indirectly using the RNG through some other API that we call, which will affect downstream calls to the RNG. This only matters when someone is say generating a dataset and then adds an additional call to an action within a sequence of other actions that use the RNG.

[Lucaweihs]

A few comments but I'm otherwise happy with this update.

[Lucaweihs]

What about the System.Random seed?

[mattdeitke]

I've added a new systemRandom variable to BaseFPSAgentController, which is now used in place of always constructing a new System.Random() object.

Some notes:

1. There was no way to set the seed of System.Random globally.
2. System.Random is necessary for generating doubles, instead of just floats (which can be done with UnityEngine.Random).
3. It is intentionally not used with a few actions that have randomSeed as a parameter. The only public one is InitialRandomSpawn, which is being reworked, such that, among other things, it will no longer have a random seed parameter.
4. After calling controller.reset(), there are no guarantees that the seeds remain in tact.

[Lucaweihs]

LGTM.