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Scena

Scena is the scenario execution engine of the Robomous toolchain — the stage where scenario actors perform.

It is an open-source (Apache-2.0) scenario execution engine for autonomous-driving simulation, developed by Robomous. It executes scenarios described in ASAM OpenSCENARIO XML (1.0–1.3) and, in later phases, ASAM OpenSCENARIO DSL (2.x) — closing the current gap of a native C++ execution engine for the DSL.

• Library first. An embeddable C++20 library with a stable C API and Python bindings. Players and CLI tools are thin consumers of that API.
• Two frontends, one runtime. OpenSCENARIO XML and OpenSCENARIO DSL compile into a common intermediate representation (the Scenario IR); a single deterministic runtime executes the IR.
• The simulator owns the clock. Step-based API (init → step(dt) → query/report state → close). No internal threads, no imposed main loop. Per-entity control ownership: each entity is driven either by the engine (default behavior) or by the host simulator (external control).
• Standards correctness. Behavior is implemented against the ASAM OpenSCENARIO specifications, which are the sole normative reference.

Architecture

flowchart LR
    subgraph Frontends
        XML["OpenSCENARIO XML 1.0–1.3<br/>(frontends/xml)"]
        DSL["OpenSCENARIO DSL 2.x<br/>(frontends/dsl, planned)"]
    end
    IR["Scenario IR<br/>entities · storyboard<br/>actions · conditions"]
    RT["Runtime<br/>deterministic scheduler<br/>condition evaluation"]
    GW["Simulator Gateway<br/>entity state in/out · road queries<br/>control ownership: engine | host"]
    HOST["Host simulator"]

    XML --> IR
    DSL -.-> IR
    IR --> RT
    RT <--> GW
    GW <--> HOST

Loading

The C API (capi/) and the Python package (python/) wrap the C++ core; the core depends on nothing above it.

Quickstart

Requirements: CMake ≥ 3.24, a C++20 compiler, Python ≥ 3.9 (for the bindings). Dependencies are fetched automatically and pinned.

# Build and run the C++ tests
cmake -B build
cmake --build build --parallel
ctest --test-dir build --output-on-failure

# Install the Python package and run the example
python -m pip install ./python
python python/examples/hello_engine.py

Or, in one line: ./scripts/build.sh.

Minimal embedding loop, in Python:

import scena as scn

scenario = scn.Scenario("demo")
scenario.add_entity(scn.Entity("ego", "ego vehicle"))
scenario.add_entry(scn.SimulationTimeCondition(at_time=2.0),
                   scn.SpeedAction("ego", target_speed=10.0))

engine = scn.Engine()
engine.init(scenario)
for _ in range(500):          # the host owns the clock
    engine.step(0.01)         # 100 Hz
print(engine.state("ego"))
engine.close()

Roadmap

Phase	Scope	Status
F0	Project scaffold + kernel skeleton: Scenario IR, deterministic clock and scheduler, step-based engine, C API and Python binding skeletons	✅ current
F1	OpenSCENARIO XML frontend + runtime core: conditions, actions, trajectories	planned
F2	OpenSCENARIO DSL frontend: parser + type checker for the finalized 2.x standard libraries	planned
F3	DSL concrete-scenario execution over the shared runtime	planned
F4	Constraint solving / abstract scenarios (feasibility-gated)	planned

Details and gate criteria: docs/roadmap/roadmap.md. Architecture decisions: docs/architecture/.

License

Apache-2.0 — see LICENSE. Third-party dependency licenses are recorded in THIRD_PARTY_LICENSES.md.

Scena implements the ASAM OpenSCENARIO standard. It is an independent project and is not affiliated with or endorsed by ASAM e.V.