Fix gravity distributions for PhysX and OvPhysX

[AntoineRichard]

Description

Scene-wide gravity randomization accepted uniform, log_uniform, and gaussian, but the PhysX and OvPhysX paths always sampled uniformly. This change forwards the validated configured distribution to both scene-wide backend paths. Newton behavior is unchanged.

The focused regression exercises full event dispatch with deterministic Gaussian sampling on both affected backends.

Tested with:

• uv run --extra test -m pytest source/isaaclab/test/envs/test_gravity_randomization.py source/isaaclab/test/envs/test_mdp_event_selectors.py -q (7 passed)
• uv run --extra test --extra ovphysx -m pytest source/isaaclab_ov/test/physics/test_ovphysx_gravity.py -q (1 passed)
• uv run isaaclab -f
• uv run python tools/changelog/cli.py check develop --include-worktree

Type of change

• Bug fix (non-breaking change which fixes an issue)

Screenshots

Not applicable.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with uv run isaaclab -f
• I have made corresponding changes to the documentation (not applicable; no public API change)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added a changelog fragment under source/<pkg>/changelog.d/ for every touched package
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[isaaclab-review-bot]

Isaac Lab Review Bot

The change correctly forwards the configured gravity distribution to the PhysX and OvPhysX scene-wide paths, with aligned documentation, regression coverage, and a package changelog fragment.

• Design and architecture: Distribution validation remains centralized in initialization, while the existing _randomize_prop_by_op abstraction handles sampling for both scene-wide backends. The Newton per-environment path and backend selection remain unchanged.
• API: The event term retains its existing signature, defaults, and units. PhysX and OvPhysX now honor the documented non-uniform distribution configurations rather than silently sampling uniformly, which is a compatible bug fix.
• Implementation: Both _call_physx and _call_ovphysx now receive the cached distribution after initialization has rejected unsupported values. The focused test covers all three supported distributions on both backend dispatch paths; it uses injected private backend attributes, creating only a minor future test-maintenance tradeoff if those internals are restructured.

No blocking issues. No inline issue met the actionable-evidence threshold; the assessment above records the review feedback.

Automated review; human maintainers own approval decisions.

[greptile-apps]

Greptile Summary

This PR forwards the configured gravity distribution to the PhysX and OvPhysX scene-wide randomization paths, updates the parameter documentation, and adds focused backend tests.

• Caches the configured distribution for stateful gravity events.
• Uses that distribution when randomizing PhysX and OvPhysX gravity.
• Adds regression coverage for uniform, log-uniform, and Gaussian dispatch.
• The newly enabled log-uniform path does not reject ordinary non-positive gravity components and can send NaN gravity to either backend.

Confidence Score: 4/5

The PR should not merge until log-uniform gravity parameters are validated or handled without passing non-finite gravity to PhysX and OvPhysX.

Forwarding log-uniform sampling exposes conventional zero and negative gravity components to logarithms, producing NaN values that are then installed as scene gravity.

Files Needing Attention: source/isaaclab/isaaclab/envs/mdp/events.py and source/isaaclab/test/envs/test_gravity_randomization.py

Important Files Changed

Filename	Overview
source/isaaclab/isaaclab/envs/mdp/events.py	Correctly forwards configured distributions, but enables log-uniform sampling without validating that all component bounds are positive.
source/isaaclab/test/envs/test_gravity_randomization.py	Verifies distribution dispatch for both backends, but mocked samplers conceal the real log-uniform domain failure.
source/isaaclab/changelog.d/antoiner-scene-gravity-distribution.rst	Accurately records the intended backend distribution fix.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    C[Event configuration] --> D{Distribution}
    D -->|uniform| U[sample_uniform]
    D -->|gaussian| G[sample_gaussian]
    D -->|log_uniform| L[sample_log_uniform]
    L --> X[log component bounds]
    X -->|zero or negative bound| N[Non-finite sampled gravity]
    U --> B[PhysX or OvPhysX set_gravity]
    G --> B
    N --> B

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_{Reviews (1): Last reviewed commit: "Honor gravity distributions on scene-wid..." | Re-trigger Greptile}

[greptile-apps]

Log-uniform produces invalid gravity

When log_uniform is configured with conventional zero or negative gravity-component bounds, this newly forwarded distribution takes their logarithms, producing non-finite values that are passed to PhysX or OvPhysX as scene gravity. Validate that log-uniform bounds are strictly positive or otherwise handle these components before calling the sampler.