Adds option for default plane color to terrain importer

[KyleM73]

Description

The default plane configuration supports setting the plane color, but this option is not currently exposed via the terrain importer. This PR adds a ``color'' field to the terrain importer that is only used for configuring a plane.

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots

Configuration:

terrain = TerrainImporterCfg(
            prim_path="/World/ground",
            terrain_type="plane",
            terrain_generator=None,
            max_init_terrain_level=None,
            collision_group=-1,
            physics_material=sim_utils.RigidBodyMaterialCfg(
                friction_combine_mode="multiply",
                restitution_combine_mode="multiply",
                static_friction=1.0,
                dynamic_friction=1.0,
            ),
            color=(1.0, 0.0, 0.0), # Red
            debug_vis=False,
        )

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[Mayankm96]

Alternate proposal: Maybe we can allow the passing of visual_material parameter instead to the ground plane? This provides more flexbility to change this plane to other texture materials.

To just change the color of the grid, perhaps we can use the diffuse_color of the default PbrMaterial.

This should avoid the need of yet another parameter and cover broader usecases

[KyleM73]

I had thought of that but wasn't sure if the ground plane supported setting material types, I just saw the option for color. I can make it pick up the diffuse_color field of the visual material to avoid adding another option though. I'll revise and request review once updated.

[Mayankm96]

That would be amazing! Thanks a lot :)

[KyleM73]

Is there any desire to allow changing properties beyond the diffuse color? in spawn_ground_plane() the color is updated here:

# Change the color of the plane
    # Warning: This is specific to the default grid plane asset.
    if cfg.color is not None:
        prop_path = f"{prim_path}/Looks/theGrid/Shader.inputs:diffuse_tint"
        # change the color
        omni.kit.commands.execute(
            "ChangePropertyCommand",
            prop_path=Sdf.Path(prop_path),
            value=Gf.Vec3f(*cfg.color),
            prev=None,
            type_to_create_if_not_exist=Sdf.ValueTypeNames.Color3f,
        )

If so, is there documentation anywhere over the corresponding property paths in PreviewSurfaceCfg? Otherwise I'll push my changes in a moment to just pick up the color from the visual material config.

[KyleM73]

Ok changes are pushed, the color for a plane can now be configured as follows:

terrain = TerrainImporterCfg(
        prim_path="/World/ground",
        terrain_type="plane",
        terrain_generator=None,
        collision_group=-1,
        physics_material=sim_utils.RigidBodyMaterialCfg(
            friction_combine_mode="multiply",
            restitution_combine_mode="multiply",
            static_friction=1.0,
            dynamic_friction=1.0,
        ),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(1.0, 0.0, 0.0)), # red
        debug_vis=False,
    )

This allows changing the color of the ground plane but does not permit changing the material. If desired I could work on a PR expanding this to include e.g. setting Mdl file textures to the ground plane, but it would require some additional work in the ground plane spawner (and I would need some documentation on the corresponding property paths).