Edit Polygon

using AbstractPlotting

points = Node(Point2f0[(0, 0), (0.5, 0.5), (1.0, 0.0)])
scene = Scene(resolution = (500, 500))
poly!(scene, points, strokewidth = 2, strokecolor = :black, color = :skyblue2, show_axis = false, scale_plot = false)
scatter!(points, color = :white, strokewidth = 10, markersize = 0.05, strokecolor = :black, raw = true)
pplot = scene[end]
push!(points[], Point2f0(0.6, -0.3))
points[] = points[]
function add_move!(scene, points, pplot)
    idx = Ref(0); dragstart = Ref(false); startpos = Base.RefValue(Point2f0(0))
    on(events(scene).mousedrag) do drag
        if ispressed(scene, Mouse.left)
            if drag == Mouse.down
                plot, _idx = mouse_selection(scene)
                if plot == pplot
                    idx[] = _idx; dragstart[] = true
                    startpos[] = to_world(scene, Point2f0(scene.events.mouseposition[]))
                end
            elseif drag == Mouse.pressed && dragstart[] && checkbounds(Bool, points[], idx[])
                pos = to_world(scene, Point2f0(scene.events.mouseposition[]))
                points[][idx[]] = pos
                points[] = points[]
            end
        else
            dragstart[] = false
        end
        return
    end
end

function add_remove_add!(scene, points, pplot)
    on(events(scene).mousebuttons) do but
        if ispressed(but, Mouse.left) && ispressed(scene, Keyboard.left_control)
            pos = to_world(scene, Point2f0(events(scene).mouseposition[]))
            push!(points[], pos)
            points[] = points[]
        elseif ispressed(but, Mouse.right)
            plot, idx = mouse_selection(scene)
            if plot == pplot && checkbounds(Bool, points[], idx)
                deleteat!(points[], idx)
                points[] = points[]
            end
        end
        return
    end
end
add_move!(scene, points, pplot)
add_remove_add!(scene, points, pplot)
center!(scene)
RecordEvents(scene, "output")