A function to create artifical snow using R base graphics and the animation package

let_it_snow.R

## Licence: GPL 2 or 3 <https://www.gnu.org/licenses/licenses.html#GPL>
## Author: Ioannis Kosmidis <i.kosmidis@ucl.ac.uk>
## Date: 21 December 2017

#' A function to create artifical snow using R base graphics and the animation package
#'
#' @param n_flakes how many flakes to throw?
#' @param fall_speed how fast should the snow fall? There will be a \code{1/fall_speed} seconds delay between moves
#' @param max_flake_size what is the maximum flake size (same as cex in \code{\link{plot}})
#' @param eps how much is the flake allowed to move to the left and to the right? (emulating wind)
#' @param path the path to the file to save the resulting GIF animation
#' @param width in pixels
#' @param height in pixels
#' @param night if \code{TRUE} then dark background otherwise white background
#'
#'
#' @details
#'
#' Result of extreme procrastination before marking pre-Xmas assessments
#'
#' @author Ioannis Kosmidis <i.kosmidis@ucl.ac.uk>
#'
#' @seealso \url{https://paulvanderlaken.com/2017/12/18/generate-snow-in-r/} for another implementation of R snow using \code{ggplot2} and \code{gganimate}
#' @examples
#'
#' if (require("animation") & require("colorspace"))
#'    let_it_snow(n_flakes = 400, width = 400, height = 400, night = TRUE)
#'
let_it_snow <- function(n_flakes = 300, fall_speed = 4, max_flake_size = 3, eps = 1e-02, night = TRUE,
                        path = "~/Downloads/snow.gif", width = 600, height = 600) {
    x <- runif(n_flakes)
    y <- runif(n_flakes)
    sizes <- runif(n_flakes, 0, max_flake_size)
    colors <- sequential_hcl(n_flakes, c = c(10, 30), l = c(30, 95), power = 0.7)
    epoch <- 0
    maxy <- 0.4
    saveGIF({
        ani.options(interval = 1/fall_speed)
        while (any(y > maxy * 3/2)) {
            par(mar = rep(1, 4) * 3, bg = if (night) "#001319" else "#F6F6F6")
            epoch <- epoch + 1
            plot(x, y, xaxt = "n", yaxt = "n", bty = "n", xlab = "", ylab = "",
                 pch = "*", xlim = c(0, 1), ylim = c(0, maxy), cex = sizes, col = colors)
            box(col = "gray", lwd = 10)
            abline(h = maxy/2, v = 0.5, col = "gray", lwd = 4)
            x <- x + runif(n_flakes, -eps, +eps)
            y <- y - runif(n_flakes, 0, 0.02)
            ani.pause()
        }}, movie.name = path, img.name = "snow", ani.height = height, ani.width = width)
}