Simulate Cloth with Visual Thickness in Isaac Sim

[itchuang]

Hello,

I am using Isaac Sim to simulate cloth, but I want to have cloth that has a visual thickness as shown in the picture below:

So far I’ve been able to create cloth that has thickness from a Cube mesh like the picture above. The issue is that this cloth acts like an inflatable, which I don’t want.

Is there any way to have visually thick cloth in Issac Sim currently?

I am using the code below to create the cloth:

scene_path = Sdf.Path("/physicsScene")
stage = get_current_stage()
default_prim_path = Sdf.Path("/World")

x_scale = 1.0
y_scale = 1.0
z_scale = 0.03
x_resolution = 25
y_resolution = int((x_resolution/x_scale) * y_scale)
z_resolution = 1

success, tmp_path = omni.kit.commands.execute(
    "CreateMeshPrimWithDefaultXform",
    prim_type="Cube",
    u_patches=x_resolution,
    v_patches=y_resolution,
    w_patches=z_resolution,
    u_verts_scale=1,
    v_verts_scale=1,
    w_verts_scale=1,
)

if not success:
    raise SystemExit("Error")

cloth_mesh_path = Sdf.Path(omni.usd.get_stage_next_free_path(stage, "/Cloth", True))
omni.kit.commands.execute("MovePrim", path_from=tmp_path, path_to=cloth_mesh_path)

cloth_mesh = UsdGeom.Mesh.Define(stage, cloth_mesh_path)
physicsUtils.setup_transform_as_scale_orient_translate(cloth_mesh)
physicsUtils.set_or_add_translate_op(cloth_mesh, Gf.Vec3f(0.0, 0.0, 10.0))
physicsUtils.set_or_add_orient_op(cloth_mesh, Gf.Quatf(1, Gf.Vec3f(0.0, 0.0, 0)))
physicsUtils.set_or_add_scale_op(cloth_mesh, Gf.Vec3f(x_scale, y_scale, z_scale))

# configure and create particle system
# we use all defaults, so the particle contact offset will be 5cm / 0.05m
# so the simulation determines the other offsets from the particle contact offset
particle_system_path = default_prim_path.AppendChild("particleSystem")

# size rest offset according to plane resolution and width so that particles are just touching at rest
radius = 0.5 * (z_scale / z_resolution / 2)
restOffset = radius
contactOffset = restOffset * 1.5

particleUtils.add_physx_particle_system(
    stage=stage,
    particle_system_path=particle_system_path,
    contact_offset=contactOffset,
    rest_offset=restOffset,
    particle_contact_offset=contactOffset,
    solid_rest_offset=restOffset,
    fluid_rest_offset=0.0,
    solver_position_iterations=16,
    simulation_owner=scene_path,
)

# create material and assign it to the system:
particle_material_path = default_prim_path.AppendChild("particleMaterial")
particleUtils.add_pbd_particle_material(stage, particle_material_path)
# add some drag and lift to get aerodynamic effects
particleUtils.add_pbd_particle_material(stage, particle_material_path, drag=0.1, lift=0.3, friction=0.6)
physicsUtils.add_physics_material_to_prim(
    stage, stage.GetPrimAtPath(particle_system_path), particle_material_path
)

# configure as cloth
stretchStiffness = 10000.0
bendStiffness = 200.0
shearStiffness = 100.0
damping = 0.2
particleUtils.add_physx_particle_cloth(
    stage=stage,
    path=cloth_mesh_path,
    dynamic_mesh_path=None,
    particle_system_path=particle_system_path,
    spring_stretch_stiffness=stretchStiffness,
    spring_bend_stiffness=bendStiffness,
    spring_shear_stiffness=shearStiffness,
    spring_damping=damping,
    self_collision=True,
    self_collision_filter=True,
)

# configure mass:
cloth_density = 1000
mass = (x_scale * y_scale * z_scale) * cloth_density
num_verts = len(cloth_mesh.GetPointsAttr().Get())
massApi = UsdPhysics.MassAPI.Apply(cloth_mesh.GetPrim())
massApi.GetMassAttr().Set(mass)

def create_pbd_material(mat_name: str, color_rgb: Gf.Vec3f = Gf.Vec3f(0.2, 0.2, 0.8)) -> Sdf.Path:
    # create material for extras
    create_list = []
    omni.kit.commands.execute(
        "CreateAndBindMdlMaterialFromLibrary",
        mdl_name="OmniPBR.mdl",
        mtl_name="OmniPBR",
        mtl_created_list=create_list,
        bind_selected_prims=False,
    )
    target_path = "/World/Looks/" + mat_name
    if create_list[0] != target_path:
        omni.kit.commands.execute("MovePrims", paths_to_move={create_list[0]: target_path})
    shader = UsdShade.Shader.Get(get_current_stage(), target_path + "/Shader")
    shader.CreateInput("diffuse_color_constant", Sdf.ValueTypeNames.Color3f).Set(color_rgb)
    return Sdf.Path(target_path)

# add render material:
material_path = create_pbd_material("OmniPBR")
omni.kit.commands.execute(
    "BindMaterialCommand", prim_path=cloth_mesh_path, material_path=material_path, strength=None
)

world.render()

[SimonPhysX]

Hi @itchuang,

Sorry for the late answer. There is no support for skinning meshes to cloth right now. You will have to implement that yourself.

Cheers,
Simon