R/plotMazeSolution.R

In Vessy/Rmaze: A package for generating mazes

#' Plot maze solution (path)
#'
#' @param gD an existing maze graph object.
#' @param nrows maze height (number of rows); default value set to 0.
#' @param ncols maze width (number of columns); default value set to 0.
#' @param inShiny a flag that marks whether the function is called from a shiny app or console.
#'
#' @return The maze solution is found as the shortest path between the start and end maze cells (currently, start and
#'  end points of the maze are fixed). The function uses ggplot to plot a maze.
#'
#' @examples
#' maze1 <- makeGraph(10, 10)
#' maze1 <- makeMaze_dfs(maze1)
#' plotMaze(maze1, 10, 10)
#' plotMazeSolution(maze1, 10, 10)
#'
#' @export

plotMazeSolution <- function(gD = NA, nrows=0, ncols=0, inShiny = FALSE){

  if (!inShiny){
    if (!exists(deparse(substitute(gD))))
      stop("A maze/graph object with the specified name does not exist!")
  }

  if (nrows <= 0)
    stop("Number of rows (height) has to be larger than zero!")

  if (ncols <= 0)
    stop("Number of columns (width) has to be larger than zero!")

  # Find the shortest path between the start and end maze cells
  # (currently, those cells are A_1_1 and A_nrows_ncols)

  # First, we need to create a subgraph that contains only edges
  # with no walls (i.e., cells where a path between two cells exist)
  gD_hlp <- igraph::subgraph.edges(gD, igraph::E(gD)[igraph::E(gD)$wall == "OFF"], delete.vertices = FALSE)

  # Now, we will find the maze solution - it will be the shortest path between the start end end maze cells
  sp_start_end <- igraph::shortest_paths(gD_hlp, igraph::V(gD_hlp)[1], igraph::V(gD_hlp)[igraph::vcount(gD_hlp)], mode="all", output="vpath")

  # Finally, we plot the maze and its solution

  # Add coordinates for the outside box
  # TBD - incoorporate start and end cells, including checking if it is outside cell
  df <- data.frame(x1 = c(0, 1, 0, ncols), y1 = c(0, 0, nrows, 0), x2 = c(0, ncols, ncols-1, ncols), y2 = c(nrows,0, nrows, nrows))
  df_solution <- data.frame(x1 = c(), y1 = c(), x2 = c(), y2 = c())

  for (r in 1:nrows)
    for (c in 1:ncols){

      if (paste("A", as.character(r), as.character(c), sep="_") %in% igraph::as_ids(sp_start_end$vpath[[1]]))
        df_solution <- rbind(df_solution, data.frame(x1 = (c-1), y1 = (r-1), x2 = c, y2 = r))

      if (r < nrows)
        if (igraph::E(gD)[paste("A", as.character(r), as.character(c), sep="_") %--% paste("A", as.character(r+1), as.character(c), sep="_")]$wall == "ON")
          df <- rbind(df, data.frame(x1 = (c-1), y1 = r, x2 = c, y2 = r))


        if (c < ncols)
          if (igraph::E(gD)[paste("A", as.character(r), as.character(c), sep="_") %--% paste("A", as.character(r), as.character(c+1), sep="_")]$wall == "ON")
            df <- rbind(df, data.frame(x1 = c, y1 = (r-1), x2 = c, y2 = r))
    }

  m <- ggplot2::ggplot(data = df)
  m <- m + ggplot2::geom_segment(ggplot2::aes(x = x1, y = y1, xend = x2, yend = y2), data = df)
  m <- m + ggplot2::theme_bw()
  m <- m + ggplot2::theme(axis.title=ggplot2::element_blank(), axis.text=ggplot2::element_blank(), axis.ticks=ggplot2::element_blank(),
                     panel.grid=ggplot2::element_blank() )

  m + ggplot2::geom_rect(data=df_solution, ggplot2::aes(xmin=x1, xmax=x2, ymin=y1, ymax=y2), fill="red", alpha=0.4)

}