ReCo.jl/graphics/center_of_mass.jl

using Luxor

using ReCo: ReCo

function gen_COM_graphics()
    box_length = 100
    box_height = 100

    L = 0.35 * box_length

    R = 0.35 * box_length

    A = -0.9 * L
    B = 0.65 * L
    pr = 0.03 * L

    Ap_vec = Vector(ReCo.Shape.project_to_unit_circle(A, L))
    Bp_vec = Vector(ReCo.Shape.project_to_unit_circle(B, L))
    for p in (Ap_vec, Bp_vec)
        p[2] *= -1
    end

    Ap = Point(Ap_vec[1], Ap_vec[2])
    Bp = Point(Bp_vec[1], Bp_vec[2])

    M = R * ((Ap + Bp) / 2)

    θ = atan(-M[2], M[1])

    COM = ReCo.Shape.project_back_from_unit_circle(θ, L)
    si, co = sincos(θ)
    COMp = R * Point(co, -si)

    ##

    graphics_export_dir = "exports/graphics/COM"
    mkpath(graphics_export_dir)

    Drawing(box_length, box_height, "$graphics_export_dir/linear.pdf")
    origin()

    setcolor("black")
    arrow(Point(-1.1 * L, 0), Point(1.2 * L, 0); arrowheadlength=0.1 * L, linewidth=0.8)

    green_orange = blend(Point(-1.5 * L, 0), Point(1.5 * L, 0))
    addstop(green_orange, 0.0, "orange")
    addstop(green_orange, (L) / (3 * L), "green")
    addstop(green_orange, (2 * L) / (3 * L), "orange")
    addstop(green_orange, 1.0, "green")
    setblend(green_orange)
    setline(0.8)
    line(Point(-L, 0), Point(L, 0), :stroke)

    setcolor("red")
    setline(0.5)
    for x in (-L, L)
        line(Point(x, 0.05 * L), Point(x, -0.05 * L), :stroke)
    end

    setcolor("cyan3")
    line(Point(0, 0.05 * L), Point(0, -0.05 * L), :stroke)

    setcolor("blue")
    for p in (A, B)
        circle(Point(p, 0), pr, :fill)
    end

    setcolor("brown")
    circle(Point(COM, 0), pr, :fill)

    setcolor("black")
    fontsize(5)
    text("x", Point(1.2 * L, 0.038 * L))
    text("-L", Point(-L - 0.07 * L, 0.18 * L))
    text("0", Point(0 - 0.035 * L, 0.18 * L))
    text("+L", Point(L - 0.07 * L, 0.18 * L))
    text("A", Point(A - 0.038 * L, -0.06 * L))
    text("B", Point(B - 0.038 * L, -0.06 * L))
    text("COM", Point(COM - 0.108 * L, -0.06 * L))

    finish()

    ##

    Drawing(box_length, box_height, "$graphics_export_dir/circular_projectiong.pdf")
    origin()

    arrow(Point(-1.2 * R, 0), Point(1.2 * R, 0); arrowheadlength=0.1 * R, linewidth=0.8)
    arrow(Point(0, 1.2 * R), Point(0, -1.2 * R); arrowheadlength=0.1 * R, linewidth=0.8)

    setcolor("black")
    fontsize(5)
    text("α", Point(1.22 * R, 0.035 * R))
    text("β", Point(-0.04 * R, -1.23 * R))

    orange_green = blend(Point(0, -R), Point(0, R), "green", "orange")
    setblend(orange_green)
    setline(0.8)
    circle(Point(0, 0), R, :stroke)

    setcolor("red")
    setline(0.5)
    line(Point(1.05 * R, 0), Point(0.95 * R, 0), :stroke)
    setcolor("cyan3")
    line(Point(-1.05 * R, 0), Point(-0.95 * R, 0), :stroke)

    setcolor("blue")
    for pp in (Ap, Bp)
        circle(R * pp, pr, :fill)
    end

    setcolor("black")
    setdash("dot")
    line(R * Ap, R * Bp, :stroke)
    line(Point(0, 0), COMp, :stroke)

    setcolor("purple1")
    circle(M, pr, :fill)

    setcolor("brown")
    circle(COMp, pr, :fill)

    finish()

    return nothing
end