Stepped contourf volcano plot in Makie

stepped_contourf_volcano_makie.jl

using GLMakie
using DelimitedFiles


volcano = readdlm(Makie.assetpath("volcano.csv"), ',', Float64)

_, _, ct = contourf(volcano; colormap = :lipari, levels = 20)


polys = ct.plots[1][1][]
level_values = ct.plots[1].color[]
level_indices = let 
    i = 0
    prev = nothing
    indices = Int[]
    for val in level_values
        if val != prev
            i += 1
        end
        push!(indices, i)
        prev = val
    end
    indices
end
colors = Makie.numbers_to_colors(ct.plots[1].color[], ct.plots[1])

f = Figure()
ax3 = Axis3(f[1, 1])

for (i, (poly, index)) in enumerate(zip(polys, level_indices))
    points = decompose(Point2f, poly.exterior)
    points_top = [Point3f(p..., index) for p in points]
    points_bottom = [Point3f(p..., index-1) for p in points]

    p = poly!(ax3, points, color = colors[i])
    Makie.transform!(p, (:xy, index))
    band!(ax3, points_bottom, points_top, color = colors[i], shading = MultiLightShading)
end

f