ReCo.jl/src/Particle.jl

using StaticArrays: SVector

mutable struct Particle
    id::Int64

    c::SVector{2,Float64} # Center
    tmp_c::SVector{2,Float64} # Temporary center

    φ::Float64 # Angle

    function Particle(id::Int64, c::SVector{2,Float64}, φ::Float64)
        return new(id, c, c, φ)
    end
end

function restrict_coordinate(value::Float64, l::Float64)
    if value < -l
        value += 2 * l
    elseif value >= l
        value -= 2 * l
    end

    return value
end

function restrict_coordinates!(p::Particle, l::Float64)
    p.tmp_c = SVector{2}(restrict_coordinate(p.tmp_c[i], l) for i in 1:2)

    return nothing
end

function minimum_image_coordinate(value::Float64, l::Float64)
    if value <= -l
        value += 2 * l
    elseif value > l
        value -= 2 * l
    end

    return value
end

function minimum_image(v::SVector{2,Float64}, l::Float64)
    return SVector{2}(minimum_image_coordinate(v[i], l) for i in 1:2)
end

function are_overlapping(p1::Particle, p2::Particle, overlapping_r²::Float64, l::Float64)
    r⃗₁₂ = p2.c - p1.c # 1 -> 2

    r⃗₁₂ = minimum_image(r⃗₁₂, l)

    distance² = r⃗₁₂[1]^2 + r⃗₁₂[2]^2

    overlapping = distance² < overlapping_r²

    return (; overlapping, r⃗₁₂, distance²)
end