Snapshots

A snapshot is a view of the current Luxor drawing in its current state, before it's been closed via finish. You can take a snapshot, then continue drawing on the current drawing.

The following code exports a series of snapshots made with snapshot, showing the state of the computation for different values of the stepby parameter. (This image is a composite of all the snapshots.)

using Luxor, ColorSchemes, Colors

function julia(z, c, maxiter::Int64)
    for n = 1:maxiter
        abs(z) > 2 ? (return n) : z = z^3 + c
    end
    return maxiter
end

function drawjulia(c::Complex, pwidth, pheight;
        klo = 0.0,
        khi = 1.0,
        cpos = Point(0, 0),
        w = 4,
        stepby=1,
        maxiterations = 300)
    xmin = cpos.x - w/2; ymin = cpos.y - w/2
    xmax = cpos.x + w/2; ymax = cpos.y + w/2
    lo = 10; hi = 2
    for col = -pwidth/2:stepby:pwidth/2
        for row = -pheight/2:stepby:pheight/2
            imagex = rescale(col, -pwidth/2, pwidth/2, xmin, xmax)
            imagey = rescale(row, -pheight/2, pheight/2, ymin, ymax)
            pixelcolor = julia(complex(imagex, imagey), c, maxiterations)
            if pixelcolor > hi
                hi = pixelcolor
            end
            if pixelcolor < lo
                lo = pixelcolor
            end
            s = rescale(pixelcolor, klo, khi)
            a = slope(Point(row, col), O)
            h, sa, l = getfield.(convert(HSL, get(ColorSchemes.inferno, s)), 1:3)
            sethue(HSL(mod(180 + 360 * a/2π, 360), sa , 2l))
            box(Point(row, -col), stepby,  stepby, :fillstroke)
        end
    end
    sethue("white")
    text("$(stepby)", boxbottomcenter(BoundingBox()) + (0, -20), halign=:center)
    snapshot(fname = "/tmp/temp-$(stepby).png")
    return lo, hi
end

function main()
    w = h = 500
    Drawing(w, h, :rec)
    fontsize(20)
    fontface("JuliaMono-Bold")
    origin()
    circle(O, w/2, :clip)
    for s in vcat(50:-5:1,1)
        l, h = drawjulia(-0.5368 + 0.0923im, w, w, maxiterations = 250,
            w=3, stepby=s, klo=1, khi=100)
    end
    finish()
    preview()
end

main()