R/riley.R

In nrennie/aRt: Generative Art with R

#' Riley
#'
#' This function generates a coloured generative art ggplot object from
#' intersecting lines.
#' Inspired by Balm by Bridget Riley.
#'
#' @param n_x Number of circles in x-direction. Default 9.
#' @param n_y Number of circles in y-direction. Default 9.
#' @param offset Numeric giving offset of y-axis. Default 3.
#' @param main_col Main colour. Default "black".
#' @param bg_col Background colour. Default "white".
#' @return A ggplot object.
#' @examples
#' riley()
#' @export

riley <- function(n_x = 9,
                  n_y = 9,
                  offset = 3,
                  main_col = "black",
                  bg_col = "white") {
  x <- -n_x:n_x
  y <- -n_y:n_y + offset
  df <- expand.grid(x = x, y = y)
  plot_data <- df |>
    dplyr::mutate(y = .data$y + c(rep(c(0.5, 0), times = n_y), 0.5)) |>
    dplyr::filter(y != min(.data$y))
  p <- ggplot2::ggplot(plot_data) +
    ggforce::geom_ellipse(
      mapping = ggplot2::aes(
        x0 = .data$x,
        y0 = .data$y,
        b = 0.35 / (((abs(.data$y) + 1))^(1 / 3)),
        a = 0.35,
        alpha = abs(.data$y),
        angle = 0
      ),
      fill = main_col,
      colour = "transparent"
    ) +
    ggplot2::coord_fixed() +
    theme_aRt(bg_col)
  q <- cowplot::ggdraw() +
    cowplot::draw_plot(p) +
    ggplot2::theme(plot.background = ggplot2::element_rect(
      fill = bg_col, colour = bg_col
    ))
  return(q)
}