R/black_hole.R

In nrennie/aRt: Generative Art with R

#' Generate black hole points
#'
#' @param r_maxi Radius of i^{th} internal circle
#' @param n Number of points per circle
#' @param lim Numeric specifying size of grid
#' @noRd

black_hole_points <- function(r_maxi, n, lim) {
  r <- 1 / sqrt(stats::runif(n)) * r_maxi
  theta <- stats::runif(n, 0, 2 * pi)
  plot_data <- tibble::tibble(
    x = cos(theta) * r,
    y = sin(theta) * r
  ) |>
    dplyr::filter(
      .data$x <= lim,
      .data$x >= -1 * lim,
      .data$y <= lim,
      .data$y >= -1 * lim
    ) |>
    dplyr::mutate(dists = sqrt((.data$x^2 + .data$y^2)) - r_maxi)
  return(plot_data)
}

#' Black Hole
#'
#' This function generates a generative art ggplot
#' object using points.
#'
#' @param r_max Vector of radii for the internal circle. Default `c(50, 150, 250, 350)`.
#' @param n Number of points per circle. Default 10000.
#' @param lim Numeric specifying size of grid. Default 400.
#' @param main_cols Vector of colours (or single colour). Default
#' `rcartocolor::carto_pal(n = 7, name = "SunsetDark")`.
#' @param bg_col Background colour. Default "black".
#' @param size Size of points. Default 0.01.
#' @param a Transparency of points. Default 0.5.
#' @param s Random seed. Default 1234.
#' @return A ggplot object.
#' @examples
#' black_hole()
#' @export

black_hole <- function(r_max = c(50, 150, 250, 350),
                       n = 10000,
                       lim = 300,
                       main_cols = rcartocolor::carto_pal(n = 7, name = "SunsetDark"),
                       bg_col = "black",
                       size = 0.01,
                       a = 0.5,
                       s = 1234) {
  plot_data <- withr::with_seed(
    seed = s,
    code = {
      plot_data <- purrr::map(.x = r_max, .f = ~ black_hole_points(.x, n, lim))
      plot_data <- dplyr::bind_rows(plot_data)
      plot_data
    }
  )

  p <- ggplot2::ggplot() +
    ggplot2::geom_point(
      data = plot_data,
      mapping = ggplot2::aes(
        x = .data$x,
        y = .data$y,
        colour = .data$dists
      ),
      size = size
    ) +
    ggplot2::coord_fixed(expand = FALSE) +
    ggplot2::scale_colour_gradientn(
      colours = ggplot2::alpha(main_cols, alpha = a)
    ) +
    theme_aRt(bg_col)
  return(p)
}