Generate a Scene with a Random Number of Objects

[afishman-openai]

Describe the feature and motivation

Apologies if this is already implemented, but I haven't been able to figure it out. I'm trying to generate a scene that places a random number of objects in a rectangle. For example, the following doesn't work:

scenic_string = """
workspace = Workspace(RectangularRegion((0, 0), 0 deg, 1.2, 1.0))
numObjects = DiscreteRange(0, 5)
for i in range(numObjects):
    new Object in workspace,
        with width 0.015,
        with length 0.015
# """
scene = scenic.scenarioFromString(scenic_string)

I'd like to be able to randomize over the number of things in my scene. Is there any way to do this currently?

Additional context

No response

Issue Submission Checklist

• I checked the open and closed issues, forum, etc. and have not found any solution

[dfremont]

Hello Adam, as you discovered, random control flow is not allowed in Scenic, and as a consequence the number of objects in a Scenic scenario must be fixed. This was a deliberate design decision with several benefits (see the original paper), but of course it's a serious restriction. We would like to relax this at some point, but it would require substantial internal changes to Scenic and we don't have an estimate for when it will happen. In the mean time, the workaround we typically use is to have a separate scenario for each possible number of objects. If the scenario can be written with a loop like yours above, rather than having separate Scenic files you can make numObjects a global parameter (e.g. param numObjects = 5), then compile the Scenic file multiple times, overriding numObjects with the constant values 0, 1, 2, etc. Something like:

for n in range(6):
  scenario = scenic.scenarioFromString(scenic_string, params={"numObjects": n})
  # generate scenes here, possibly save the results somewhere, etc.