R/addImg.R

In marchtaylor/sinkr: Collection of functions with emphasis in multivariate data analysis

#' Add image to plot region
#'
#' @param obj an image file imported as an array (e.g. png::readPNG, jpeg::readJPEG)
#' @param x mid x coordinate for image
#' @param y mid y coordinate for image
#' @param width width of image (in x coordinate units)
#' @param interpolate (passed to graphics::rasterImage) A 
#'   logical vector (or scalar) indicating whether to apply 
#'   linear interpolation to the image when drawing. 
#'
#' @return adds graphics to plot
#' 
#' @importFrom graphics rasterImage
#' @export
#'
#' @examples
#' 
#' \donttest{
#' library(png)
#' myurl <- paste0("https://upload.wikimedia.org/wikipedia/commons/thumb/", 
#'   "e/e1/Jupiter_%28transparent%29.png/242px-Jupiter_%28transparent%29.png")
#' myurl <- paste0("https://upload.wikimedia.org/wikipedia/commons/4/47/",
#'   "PNG_transparency_demonstration_1.png")
#' z <- tempfile()
#' download.file(myurl,z,mode="wb")
#' pic <- readPNG(z)
#' file.remove(z) # cleanup
#' dim(pic)
#' 
#' image(volcano)
#' addImg(pic, x = 0.3, y = 0.5, width = 0.5)
#' }
#' 
addImg <- function(
  obj, # an image file imported as an array (e.g. png::readPNG, jpeg::readJPEG)
  x = NULL, # mid x coordinate for image
  y = NULL, # mid y coordinate for image
  width = NULL, # width of image (in x coordinate units)
  interpolate = TRUE # (passed to graphics::rasterImage) A logical vector (or scalar) indicating whether to apply linear interpolation to the image when drawing. 
){
  if(is.null(x) | is.null(y) | is.null(width)){stop("Must provide args 'x', 'y', and 'width'")}
  USR <- par()$usr # A vector of the form c(x1, x2, y1, y2) giving the extremes of the user coordinates of the plotting region
  PIN <- par()$pin # The current plot dimensions, (width, height), in inches
  DIM <- dim(obj) # number of x-y pixels for the image
  ARp <- DIM[1]/DIM[2] # pixel aspect ratio (y/x)
  WIDi <- width/(USR[2]-USR[1])*PIN[1] # convert width units to inches
  HEIi <- WIDi * ARp # height in inches
  HEIu <- HEIi/PIN[2]*(USR[4]-USR[3]) # height in units
  rasterImage(image = obj, 
    xleft = x-(width/2), xright = x+(width/2),
    ybottom = y-(HEIu/2), ytop = y+(HEIu/2), 
    interpolate = interpolate)
}