softbody2d

2d · physics · 56 properties · 2D

A deformable 2D body: particles linked by elastic constraints, laid out by kind and made of what the material rows say. A polygon on the same node is drawn from the solver's positions when the two agree on the vertex count, which the polygon, trimesh and volumetric kinds give and a generator does not.

In a scene, softbody2d is the node key that applies it. A script reaches each property below as a field on node.softbody2d: reading one asks the running component, and assigning one leaves the rest alone. The whole table is node.softbody2d.get() and node.softbody2d.set(table).

Properties

property	type	default	description
a	vec2	[0,0]	Where a rope starts, relative to the node
b	vec2	[0,-1]	Where a rope ends, relative to the node
bend_damping	float	1	The damping ratio of the bending springs Range 0–100.
bend_frequency	float	10	The same for the bending edges, which are what stop a cloth folding flat Range 0–10000.
can_sleep	bool	true	Let the body stop being simulated once it settles
cell_model	enum	volume	What a cell resists with: a volume constraint for a cheap jelly, or an elastic model a Young modulus parameterises One of volume, corotational, neo_hookean.
cell_size	float	0.25	How big one triangle is when a volumetric body fills an outline; smaller is finer, slower and stiffer to tear At least 0.001.
cells	vec2	[4,4]	How many cells along each axis of a grid
deformation_damping	float	0	How fast the particles are pulled towards the body's own rigid motion, which settles a residual sway without slowing the body down Range 0–1000.
dominance	int	0	Which body wins a contact: a higher one is never pushed by a lower one Range -127–127.
edge_damping	float	1	The damping ratio of that spring; 1 settles without overshooting Range 0–100.
edge_frequency	float	30	The frequency of the spring a structural edge is solved as, in hertz; higher is stiffer Range 0–10000.
edge_plastic_creep	float	1	How fast, per second, an edge's excess strain is absorbed into its rest length At least 0.
edge_plastic_flow	enum	both	Whether an edge sets under a squeeze, a stretch, or both: clay dents but does not stay stretched One of both, compression, tension.
edge_plastic_max	float	0.5	The largest permanent set an edge may take, as a fraction of its first length At least 0.
edge_plastic_yield	float	0	The edge strain past which its rest length flows towards its current length At least 0.
elastic_damping	float	1	Damping ratio of the elastic cells Range 0–100.
friction	float	0.5	Surface friction of the body's collider; 0 is ice At least 0.
gravity_scale	float	1	How much gravity pulls on the particles
half_extents	vec2	[0.5,0.5]	Half-sizes of the sheet, when kind is grid
interior_strength	float	1	How many times tougher an undamaged inside element is than a surface one, so cracks start at the surface and run inward At least 1.
kind	enum	grid	How the body's particles and elements are laid out One of grid, disk, polygon, rope, volumetric, trimesh, polyline.
layers	flags	["0"]	The layers this body is on One of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31.
linear_damping	float	0	Air friction on the particles At least 0.
mask	flags	[]	The layers it collides with; empty means every layer One of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31.
mass	float	1	What the whole body weighs, spread over its particles At least 0.
max_tears_per_step	float	0	The most edges that may tear in one step, which paces a crack; 0 is no limit At least 0.
mesh	asset · mesh	—	Points and triangles for a polygon, trimesh, polyline or volumetric body: the same asset a polygon draws
min_piece	float	0	The smallest piece, in elements, a tear may split off; 0 lets rapier choose At least 0.
oriented	bool	false	Treat the surface as closed and outward-facing, so its inside holds bodies in instead of pushing them out
particle_radius	float	0	How thick the particles are; 0 takes what the layout works out At least 0.
particles	float	16	How many particles a rope or the rim of a disk is made of At least 2.
pgs_iterations	float	3	Extra iterations inside each substep, for the same Range 0–64.
pinned	list	[]	The particles held where they are, by index: a cloth hangs from these, and softbody_particles says how many there are to choose from
plastic_creep	float	1	How fast, per second, the strain past the yield is absorbed into the rest shape At least 0.
plastic_max	float	1	The most permanent deformation a cell may take, so a crushed cell cannot flow to a sliver At least 0.
plastic_yield	float	0	The cell strain past which the rest shape flows towards the current one; 0 is perfectly elastic At least 0.
poisson_ratio	float	0.3	How much an elastic cell bulges sideways when squeezed; towards 0.5 it stops changing volume at all Range 0–0.499.
radius	float	0.5	Radius, when kind is disk At least 0.001.
restitution	float	0	Bounciness of the body's collider Range 0–1.
self_contacts	bool	false	Let the body's own surface collide with itself, which stops a cloth passing through its own fold
shape_matching	bool	false	Pull the body back towards the shape it was built in, which is what keeps a jelly a jelly
shape_matching_damping	float	1	The damping ratio of the shape-matching constraints Range 0–100.
shape_matching_frequency	float	10	The same for shape matching, which pulls the body back towards the shape it was built in Range 0–10000.
skin	bool	false	Keep the outline as the drawn shape and let the cells carry it, so a detail the cell size cannot resolve survives
solver	enum	constraints	Which solver runs the elasticity: sequential constraints, or an implicit Euler step over the whole body One of constraints, fem.
solver_iterations	float	0	Extra solver substeps for this body and everything it touches Range 0–64.
tear_force	float	0	The pull past which an edge breaks; 0 is unbreakable. Either criterion tears an edge At least 0.
tear_smoothing	float	0	Over how many seconds a load is averaged before it is tested, so one hard frame does not tear a body At least 0.
tear_strain	float	0	The stretch past which an element breaks, as a fraction of its rest length; 0 is unbreakable At least 0.
tension_only	bool	false	Let the edges resist stretching only, so the body folds freely and never pushes itself open
volume_damping	float	1	The damping ratio of the volume constraints Range 0–100.
volume_factor	float	1	What that volume is held at, as a multiple of the rest volume; above 1 inflates the body At least 0.
volume_frequency	float	30	The same for the constraints holding a cell's volume, and for the whole-body one Range 0–10000.
volume_preservation	bool	false	Hold the volume each closed piece of the body encloses
young_modulus	float	10000	Stiffness of the elastic cells, as force per unit area; a finer mesh does not get stiffer for it At least 0.

Asset types this component references: mesh.

Script functions

Methods of node.softbody2d, the handle a node carrying this component exposes. Every handle also has get(), set(table), patch(table), has() and remove().

From physics2d:

method	what it does
pin_particle(int)	Hold one particle where it is, which is how a cloth hangs from a hook.
set_softbody(any)	Build the node's soft body from a softbody2d table: kind, the shape rows, and the material rows.
softbody_area() -> float	How much area the body encloses right now, against softbody_rest_area for how far it is squeezed.
softbody_center() -> any	The body's centre of mass, which is where it is when a deformable body has no one position.
softbody_particles() -> int	How many particles the body ended up with, which a generator decides rather than the author.
softbody_position(int) -> any	Where one particle is, in world space.
softbody_rest_area() -> float	How much it encloses at rest.