Like PhysX, it is possible to apply forces to Flex objects either implicitly (i.e. letting objects fall to due gravity) or explicitly (i.e. by adding a force to the physics engine).
The simplest way to apply a force to a Flex object is to send apply_force_to_flex_object:
from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.third_person_camera import ThirdPersonCamera
from tdw.add_ons.image_capture import ImageCapture
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH
c = Controller()
camera = ThirdPersonCamera(avatar_id="a",
position={"x": 3.83, "y": 3.6, "z": -0.71},
look_at={"x": 0, "y": 0, "z": 0})
path = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("apply_force_to_flex_object")
print(f"Images will be saved to: {path}")
capture = ImageCapture(avatar_ids=["a"], path=path)
c.add_ons.extend([camera, capture])
cube_id = c.get_unique_id()
c.communicate([TDWUtils.create_empty_room(12, 12),
{'$type': 'convexify_proc_gen_room'},
{'$type': 'create_flex_container'},
c.get_add_object(model_name="cube",
object_id=cube_id,
library="models_flex.json",
position={"x": 0, "y": 0, "z": 0}),
{'$type': 'set_flex_soft_actor',
'id': cube_id,
'particle_spacing': 0.125,
'cluster_stiffness': 0.22},
{"$type": "assign_flex_container",
"id": cube_id,
"container_id": 0},
{"$type": "apply_force_to_flex_object",
"force": {"x": 2000, "y": 0.0, "z": 0},
"id": cube_id}])
for i in range(200):
c.communicate([])
c.communicate({"$type": "terminate"})Result:
It is also possible to apply forces to individual particles. To do this, you'll need to first request FlexParticles output data and then send apply_forces_to_flex_object_base64.
apply_forces_to_flex_object_base64 encodes particles and forces in a base64 string.
The array is arranged as such:
forces = [f0_x, f0_y, f0_z, id0, f1_x, f1_y, f1_z, id1 ... ]
Where f values are coordinates for the force vector and id values are the particle IDs (see above).
To encode forces to base64 correctly, use TDWUtils.get_base64_flex_particle_forces(forces).
This controller will apply forces only to the topmost particles of a cube:
from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.third_person_camera import ThirdPersonCamera
from tdw.add_ons.image_capture import ImageCapture
from tdw.backend.paths import EXAMPLE_CONTROLLER_OUTPUT_PATH
from tdw.output_data import OutputData, FlexParticles
c = Controller()
camera = ThirdPersonCamera(avatar_id="a",
position={"x": 3.83, "y": 3.6, "z": -0.71},
look_at={"x": 0, "y": 0, "z": 0})
path = EXAMPLE_CONTROLLER_OUTPUT_PATH.joinpath("apply_forces_to_flex_object_base64")
print(f"Images will be saved to: {path}")
capture = ImageCapture(avatar_ids=["a"], path=path)
c.add_ons.extend([camera, capture])
cube_id = c.get_unique_id()
resp = c.communicate([TDWUtils.create_empty_room(12, 12),
{'$type': 'convexify_proc_gen_room'},
{'$type': 'create_flex_container'},
c.get_add_object(model_name="cube",
object_id=cube_id,
library="models_flex.json",
position={"x": 0, "y": 0, "z": 0}),
{'$type': 'set_flex_soft_actor',
'id': cube_id,
'particle_spacing': 0.125,
'cluster_stiffness': 0.22},
{"$type": "assign_flex_container",
"id": cube_id,
"container_id": 0},
{"$type": "send_flex_particles",
"frequency": "once"}])
# The forces and IDs, arranged as: [f0_x, f0_y, f0_z, id0, f1_x, f1_y, f1_z, id1 ... ]
particle_forces_and_ids = []
for i in range(len(resp) - 1):
r_id = OutputData.get_data_type_id(resp[i])
if r_id == "flex":
flex_particles = FlexParticles(resp[i])
# Get the particles for the cube.
for j in range(flex_particles.get_num_objects()):
if flex_particles.get_id(j) == cube_id:
particles = flex_particles.get_particles(j)
# Iterate through the particles. The ID is the index.
for particle_id in range(len(particles)):
# Get the y value of the particle.
if particles[particle_id][1] > 0.75:
# Apply a force to this particle.
particle_forces_and_ids.extend([10, 0, 0, particle_id])
# Encode the force.
force_string = TDWUtils.get_base64_flex_particle_forces(forces=particle_forces_and_ids)
# Apply the force.
c.communicate({"$type": "apply_forces_to_flex_object_base64",
"forces_and_ids_base64": force_string,
"id": cube_id})
for i in range(200):
c.communicate([])
c.communicate({"$type": "terminate"})Result:
Next: Reset a Flex scene
Example controllers:
- apply_forces_to_flex_object_base64.py Apply forces to individual Flex particles.
- apply_force_to_flex_object.py Apply a directional force to a Flex soft-body object.
Python API:
Command API:
Output Data: