Code Sketch

def triangle(size: Double) = Picture {
    left(5)
    forward(size)
    right(92)
    forward(size / 10)
    right(94)
    forward(size)
}

def illusion(n: Int, size: Double): Picture = {
    if (n == 1) {
        triangle(size)
    }

    else {
        picStack(
            penColor(noColor) * fillColor(black) -> triangle(size),
            penColor(noColor) * rot(9) -> illusion(n - 1, size)
        )
    }
}

cleari()
clearOutput()
val bgclr = cm.radialGradient(0, 0, cm.gray, 80, cm.white, false)
setBackground(bgclr)
draw(illusion(42, 200))