Generate guides for making a poster in inkscape

guide_generator.R

#' Get the size of a single panel
#'
#' @param n the number of panels
#' @param len the overall length of the side
#' @param margin the outer margin width (will be multiplied by 2)
#' @param gutter the space between panels
#'
#' @return a numeric value specifying the panel width/length
#'
#' @examples
#' get_panel_size()
get_panel_size <- function(n = 4, len = 48, margin = 1, gutter = 0.5){
  all_gutters <- (n - 1) * gutter
  panel_size  <- (len - margin - margin - all_gutters)/n
  return(panel_size)
}

#' Get the size of a single panel
#'
#' @param n the number of panels
#' @param len the overall length of the side
#' @param margin the outer margin width (will be multiplied by 2)
#' @param gutter the space between panels
#'
#' @return a numeric vector delimiting the panels.
#'
#' @examples
#' get_guides()
#' diff(get_guides()) # note the differences are either the gutter or panel size
#' get_panel_size()
get_guides <- function(n = 4, len = 48, margin = 1, gutter = 0.5){
  panel_size <- get_panel_size(n = n, len = len, margin = margin, gutter = gutter)
  inner <- seq(from = 1, to = n - 1)
  mat   <- matrix(0.0, ncol = n - 1, nrow = 2)
  gutters  <- cumsum(rep(gutter, n - 1)) - gutter # the cumulative gutters, starting at 0
  panels   <- (panel_size * inner) + gutters # panels and left gutters
  mat[1, ] <- panels + margin    # shifting by left margin
  mat[2, ] <- mat[1, ] + gutter  # adding the right gutters
  c(margin, mat, len - margin)   # putting it all together
}
#
# An example 36x48 poster with 1.5 inch margins and a half an inch gutter and
# six panels.
if (interactive()){
  (columns <- get_guides(n = 3, len = 48, margin = 1.5, gutter = 0.5))
  (rows    <- get_guides(n = 2, len = 36, margin = 1.5, gutter = 0.5))
  plot(0, 0, xlim = c(0, 48), ylim = c(0, 36), asp = 1,
       ann = F, bty = 'n', type = 'n', xaxt = 'n', yaxt = 'n')
  rect(0, 0, 48, 36, col = "grey98")
  abline(v = columns, col = "blue", lty = 2)
  abline(h = rows, col = "blue", lty = 2)
}

Here's the output of the example: