Resolve "Normalize dimension of images in report"

Closes #6 (closed)

R/plot_png.R

+#' Plot a PNG file
+#'
+#' @details
+#' This function offers two advantages for displaying images in reports
+#' or vignettes instead of markdown syntax or [knitr::include_graphics()]:
+#' - The size of the image is controlled by the chunk parameters
+#' - Image files stored outside the report or vignette folder are correctly
+#' rendered in HTML
+#'
+#' @source From https://stackoverflow.com/a/28729601/5300212
+#' @param path Path of the file
+#' @param add [logical] Add the image to the existing plot
+#'
+#' @return Nothing, used to side effect.
+#' @export
+#'
+#' @examples
+#' plot_png(system.file("img", "Rlogo.png", package="png"))
+plot_png <- function(path, add = FALSE) {
+  # read the file
+  pic <- png::readPNG(path, native = TRUE)
+  res <- dim(pic)[2:1] # get the resolution, [x, y]
+  if (!add) {
+    opar <- par(mar = c(0, 0, 0, 0))
+    plot(
+      1,
+      1,
+      xlim = c(1, res[1]),
+      ylim = c(1, res[2]),
+      asp = 1,
+      type = 'n',
+      xaxs = 'i',
+      yaxs = 'i',
+      xaxt = 'n',
+      yaxt = 'n',
+      xlab = '',
+      ylab = '',
+      bty = 'n'
+    )
+    par(opar)
+  }
+  graphics::rasterImage(pic, 1, 1, res[1], res[2], xpd = TRUE)
+}