sierpinski.R

# http://qiita.com/HikaruR/items/c67b6c9714c51d70333c
# accessed on 2017-06-23

elem_n <- function(n, ...) {
    dots <- list(...)
    unlist(lapply(dots, `[`, n))
}

polygon_y123 <- function(y1, y2, y3, ...) {
    polygon(x = elem_n(1, y1, y2, y3), y = elem_n(2, y1, y2, y3), ...)
}

Sierpinski.gasket2 <- function(depth,
                               y1 = c(0, 1),
                               y2 = c(-1, -1),
                               y3 = c(1, -1)
                               ) {
    if (depth > 15) {
        stop("may be too deep to draw chart")
    }
    plot.new()
    plot.window(xlim = range(elem_n(1, y1, y2, y3)), 
                ylim = range(elem_n(2, y1, y2, y3)))

    # most-out boader
    polygon_y123(y1, y2, y3, col = "gray")
    
    (function(d, y1, y2, y3) {
        if (d == 0) {
            return(invisible())
        }

        y12 = (y1 + y2) / 2
        y23 = (y2 + y3) / 2
        y13 = (y1 + y3) / 2
        polygon_y123(y12, y13, y23, col = "white")
        Recall(d - 1, y1, y12, y13)
        Recall(d - 1, y12, y2, y23)
        Recall(d - 1, y13, y23, y3)
        invisible()
    })(depth, y1, y2, y3)
}

Sierpinski.gasket2(5)