julia bouncing balls

julia-bouncing-balls-animation.jl

#!/usr/bin/env julia

using Luxor, Colors, Combinatorics

mutable struct Ball
    id::Int
    position::Point
    velocity::Point
    color::Color
    ballradius::Float64
end

function backdropf(scene, framenumber)
    background("white")
end

function collisioncheck(balls)
    for ballpair in combinations(1:length(balls), 2)
        balla, ballb = balls[ballpair[1]], balls[ballpair[2]]
        if intersection2circles(
            balla.position,
            balla.ballradius,
            ballb.position,
            ballb.ballradius,
        ) > 0.01
            collision = ballb.position - balla.position
            distance = Luxor.distance(ballb.position, balla.position)
            # Get the components of the velocity vectors which are parallel to the collision.
            # The perpendicular component remains the same for both
            collision = (collision / distance)
            aci = dotproduct(balla.velocity, collision)
            bci = dotproduct(ballb.velocity, collision)

            # new velocities using the 1-dimensional elastic collision equations
            # masses are the same
            acf = bci
            bcf = aci
            # replace the velocity components
            balls[ballpair[1]].velocity += (acf - aci) * collision
            balls[ballpair[2]].velocity += (bcf - bci) * collision
        end
    end
    return balls
end

function update(scene, framenumber, balls)
    setopacity(0.9)
    panes = Tiler(scene.movie.width, scene.movie.height, 1, 2, margin = 0)
    panecenters = first.(collect(panes))
    panewidth = panes.tilewidth / 2
    paneheight = panes.tileheight / 2
    balls = collisioncheck(balls)
    # on the left 
    @layer begin
        translate(panecenters[1])
        box(O1, 2panewidth, 2paneheight, :stroke)
        for ball in balls
            ball.position = ball.position += ball.velocity
            if (ball.position.x <= (-panewidth + ball.ballradius))
                ball.position = Point(-panewidth + ball.ballradius, ball.position.y)
                ball.velocity = Point(-ball.velocity.x, ball.velocity.y)
            end
            if (ball.position.x >= (panewidth - ball.ballradius))
                ball.position = Point(panewidth - ball.ballradius, ball.position.y)
                ball.velocity = Point(-ball.velocity.x, ball.velocity.y)
            end
            if (ball.position.y <= (-paneheight + ball.ballradius))
                ball.position = Point(ball.position.x, -panewidth + ball.ballradius)
                ball.velocity = Point(ball.velocity.x, -ball.velocity.y)
            end
            if (ball.position.y >= (paneheight - ball.ballradius))
                ball.position = Point(ball.position.x, panewidth - ball.ballradius)
                ball.velocity = Point(ball.velocity.x, -ball.velocity.y)
            end
            sethue(ball.color)
            circle(ball.position, ball.ballradius, :fill)
        end
    end
    # do the right thing
    @layer begin
        sethue("black")
        fontsize(14)
        fontface("Menlo")
        translate(panecenters[2])
        data = [(b.position.x, b.position.y) for b in balls]
        stringdata = map(x -> string(convert.(Int, floor.(x))), data)
        textbox(stringdata, O - (panewidth, paneheight) + (5, 5), leading = 20)
    end
end

function main()
    juliaballmovie = Movie(256, 128, "juliaballs")
    initialpts = ngon(O + (0, 10), 35, 3, pi / 6, vertices = true)
    ballradius = 14
    balls = [
        # set position and initial velocity vectors
        Ball(1, initialpts[1], initialpts[3] / 30, colorant"brown3", ballradius),
        Ball(2, initialpts[2], initialpts[2] / 30, colorant"forestgreen", ballradius),
        Ball(3, initialpts[3], initialpts[1] / 40, colorant"mediumorchid3", ballradius),
    ]
    animate(
        juliaballmovie,
        [
            Scene(juliaballmovie, backdropf, 1:100),
            Scene(juliaballmovie, (s, f) -> update(s, f, balls), 1:100),
        ],
        framerate = 30,
        creategif = true,
        pathname = "juliapool.gif",
    )
end

main()