Julia code that reproduces Jeremy Hinton's "Lilac Chaser" illusion. See https://michaelbach.de/ot/col-lilacChaser/ for more information on how the illusion works.

lilac_chaser.jl

using Javis

video = Video(500, 500)
N = 12
frames = 4(N+1)

Background(1:frames, (args...) -> background("grey70"))

# Draw crosshairs
Object(@JShape begin
    sethue("black")
    setline(2)
    line(Point(0, 25), Point(0, -25), action=:stroke)
    line(Point(25, 0), Point(-25, 0), action=:stroke)
end)

# Draw the magenta circles and flash them on and off
for i in 1:N
    θᵢ = (2π/N)*i
    pᵢ = 200*Point(cos(θᵢ), sin(θᵢ))
    magenta_to_grey = blend(pᵢ, 1, pᵢ, 50, "magenta", "grey70")
    Cᵢ = Object(@JShape begin
        setblend(blend)
        circle(pᵢ, 50, :fill)
    end blend=magenta_to_grey)
    allgrey = blend(pᵢ, 50, pᵢ, 50, "grey70", "grey70")
    act!(Cᵢ, Action(4i:4i, change(:blend, allgrey)))
    act!(Cᵢ, Action(4i+4:4i+4, change(:blend, magentablend)))
end

render(video, pathname="lilac_chaser.gif", framerate=50)