Use default ground planes in MPM demos

[maxkra15]

Description

Use the default GroundPlaneCfg appearance in the granular, two-way coupling, and snowball MPM demos. This removes per-demo size and color overrides and keeps the examples aligned with the standard Isaac Lab ground plane.

No new dependencies.

Type of change

• Documentation/example cleanup (non-breaking)

Release backport

• Backport this pull request to the active release branch after it merges into develop

Screenshots

Not applicable; this intentionally adopts the standard ground-plane appearance.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks on all changed files
• Documentation changes are not required
• My changes generate no new warnings
• Tests are not required for configuration-only demo cleanup
• Changelog fragments are not required because no source package is changed
• My name already exists in CONTRIBUTORS.md

[isaaclab-review-bot]

Isaac Lab Review Bot

The three MPM demos now use the shared GroundPlaneCfg defaults instead of local size and color overrides. The changed scene entries preserve their prim paths and positioning, with no concrete issue identified in the supplied patch.

• Design and architecture: The ground remains an AssetBaseCfg within each existing InteractiveSceneCfg; no scene ownership or solver responsibility changes. In snowball_smash.py, the separate hidden MPM collision slab remains explicitly sized and unchanged.
• API: No public symbols, config fields, CLI arguments, or exports are changed. Existing ground prim paths and the two-way coupling demo’s -wall_t ground offset are preserved.
• Implementation: The implementation consistently removes only the explicit ground-plane size and color arguments in all three demos. Surrounding collider, bath, crate, and MPM-ground configuration paths are unchanged. The intended tradeoff is that ground dimensions and appearance now follow shared defaults rather than demo-specific values.

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 standardizes three MPM demos on the default Isaac Lab ground-plane configuration.

• Replaces explicit 12×12 m ground sizes with the default 100×100 m visual mesh.
• Replaces custom dark-gray tints with the default warm-white ground and green metric grid.
• Preserves existing ground placement and physics behavior.

Confidence Score: 5/5

The PR appears safe to merge because the changes affect ground-plane visual size and appearance without altering collision coverage or scene containment.

No actionable failure remains: the ground collision is an infinite plane, all scenes fit within the former and new visual footprints, and the translated two-way coupling ground retains its existing position.

Important Files Changed

Filename	Overview
scripts/demos/mpm/newton_mpm_granular.py	Uses the default ground-plane size and appearance; the granular scene remains within the plane’s prior footprint.
scripts/demos/mpm/newton_mpm_twoway_coupling.py	Uses the default ground-plane configuration while preserving its translated placement beneath the bath.
scripts/demos/mpm/snowball_smash.py	Uses the default visible ground plane while retaining the separate 12×12 m hidden MPM collision slab.

_{Reviews (1): Last reviewed commit: "Use default ground planes in MPM demos" | Re-trigger Greptile}

[AntoineRichard]

run-ci