function rhue(a)
    local R = math.random(35, 75) / 100
    local G = math.random(35, 75) / 100
    local B = math.random(35, 75) / 100
    local A = a or math.random()

    return vec4(R, G, B, A)
end

function rmono()
    return vec4(1, 1, 1, math.random())
end


function show_axes()
    xaxis = am.line(vec2(win.left, 0), vec2(win.right, 0))
    yaxis = am.line(vec2(0, win.top), vec2(0, win.bottom)) 
    world:append(am.group{xaxis, yaxis}:tag("axes"))
end