function Entity(; kwargs...)

Create an Entity representing a body in the simulation.

Keywords

• name::Symbol: The name for the entity. Necessary, and must be distinct from all other entities in the World.
• shape::AbstractShape{2} = nothing: The shape of the entity, specified as a 2D primitive from PrimitiveCollisions.jl. Can also be nothing, which removes the entity from the simulation.
• position::SVector{2,Float64} = @SVector[0.0, 0.0]: The initial position of the entity.
• velocity::SVector{2,Float64} = @SVector[0.0, 0.0]: The initial velocity of the entity.
• rotation::Float64 = 0.0: The initial rotation of the entity. Specified in radians in an anticlockwise direction from the positive x-axis.
• angular_velocity::Float64 = 0.0: The initial angular velocity of the entity. Specified in radians per second, in the same direction as rotation.
• mass::Float64 = 1.0: The mass of the entity. Can be Inf to make the body immovable.
• inertia::Float64 = 1.0: The moment of inertia ("rotational mass") of the entity. Can be Inf to make the body impossible to rotate.
• linear_drag::Float64 = 0.1: The linear drag coefficient. Linear drag force is calculated as the product of this coefficient and the negative of the velocity of the entity.
• angular_drag::Float64 = 0.1: The angular drag coefficient. Angular drag torque is calculated as the product of this coefficient and the negative of the angular velocity of the entity.
• bounce::Float64 = 1.0: The coefficient of restitution used during collision resolution is taken as the minimum of the bounce values of the two involved bodies. Typically in the range [0.0, 1.0]. 1.0 is a perfectly elastic collision, 0.0 is a perfectly inelastic collision.

Symbolic variables

In the ODESystem returned by get_system the variables/parameters for an entity are referred to by sightly different names, prefixed by the name of the entity followed by an underscore (_). Following are the names ($name_ is the prefix):

• $name_pos(t)[1:2]: Position
• $name_vel(t)[1:2]: velocity
• $name_acc(t)[1:2]: Acceleration
• $name_θ(t): Rotation
• $name_ω(t): Angular velocity
• $name_α(t): Angular acceleration
• $name_m: Mass
• $name_I: Moment of inertia
• $name_μ: Linear drag coefficient
• $name_η: Angular drag coefficient

function Entity(template::Entity; kwargs...)

Create an copy of an existing entity template, with some values modified. Keyword arguments are the same as in the keyword constructor, and name must be specified regardless.

function Simulation(world::World, gravity = [0.0, -9.81])

Return a Simulation for the given world, which can be stepped using DifferentialEquations.step! to advance the simulation. Creates the system using get_system, and adds a callback for collision detection. The solver used is AutoTsit5(Rosenbrock23()). The underlying integrator is available as sim.integrator, and intermediate states are not saved during simulation.

function World(name::Symbol)

Creates a world containing all Entitys to be simulated. The system returned from get_system is named name. Entities can be added to a world using Base.push!. Base.getindex returns an Entity given its name. Base.haskey checks whether an entity with the given name exists in this world. Base.delete! deletes the entity with the given name from the world.

function Base.delete!(w::World, sym::Symbol)

Remove the Entity with the name sym from the given World.

function Base.getindex(w::World, sym::Symbol)

Return the Entity with name sym in World.

function Base.haskey(w::World, sym::Symbol)

Check whether the World contains an entity with name sym.

function Base.push!(w::World, e::Entity)

Add the given Entity to the given World.

function get_self_equations(ent::Entity{S}, sts, prs, gravity)

Given an entity, its symbolic states and parameters, and the force of gravity, returns the equations of motion for the entity.

function get_symbols(ent::Entity)

Get the symbolic variables and parameters for the given entity, in a NamedTuple.

function get_system(w::World, gravity = [0.0, -9.81])

Return the ODESystem for the given [World]. Uses the provided value for the acceleration due to gravity, exposed in the ODESystem as g.

function DifferentialEquations.step!(sim::Simulation, args...)

Steps the given [Simulation]. args... are forwarded to DifferentialEquations.step!. See the relevant DiffEq docs for further information.