include_graphics.R

#' Include an image not produced in Rmd/Rnw file.
#'
#' @param image_file character. image file name. Typically, PNG JPEG or SVG file.
#' @param html_opts list. list of \code{alt} and \code{width}. 
#'   Used as alt/width attributes for the image tag.
#' @param latex_opts list. list of parameters passed to \\includegraphics[]{image_file}
#'
#' @return LaTeX/Markdown code embedded in Rmd/Rnw file.
#' @export
include_graphics <- function(image_file, html_opts = NULL, latex_opts = NULL) {
  
  if (length(image_file) > 1) {
    message("include_graphis supports a single file only. The first item will be used.")
    image_file = image_file[[1]]
  }
  
  sys_call <- sys.calls()
  sys_call <- sapply(sys_call, deparse)
  use_knitr <- any(grepl('knitr::knit', sys_call))
  use_pandoc <- any(grepl('pandocwrite', sys_call))
  to_pdf <- exams::match_exams_device() == 'pdf'
  
  converter <- exams:::.exams_internal$xexams_call[[1]]$converter
  if (identical(converter, 'tex2image')) {
    stop('converter = "tex2image" is currently not supported.')
  }
  
  pdf_file <- paste0(tools::file_path_sans_ext(image_file), '.pdf')
  if (to_pdf && file.exists(pdf_file)) {
    image_file <- tools::file_path_sans_ext(image_file)
  }
  
  # Options
  # ==========
  # latex_opts
  # ----------
  # (1) Rnw -> LaTeX -> PDF
  # (2) Rmd -> MD -> (Pandoc) -> LaTeX -> PDF
  # (3) Rnw -> LaTeX -> (Pandoc) -> HTML
  #
  # html_opts
  # ---------
  # (4) Rnw -> LaTeX -> (tth/ttm) -> HTML
  # (5) Rmd -> MD -> (Pandoc) -> HTML
  #
  
  if (!is.null(latex_opts)) {
    latex_before <- latex_opts$before
    latex_after <- latex_opts$after
    latex_opts$before <- latex_opts$after <- NULL
    latex_options <- paste(paste(names(latex_opts), latex_opts, sep = '='), collapse = ', ')
  } else {
    latex_before <- latex_after <- NULL
    latex_options <- NULL
  }
  
  if (!is.null(html_opts)) {
    html_before <- html_opts$before
    html_after <- html_opts$after
    html_opts$before <- html_opts$after <- NULL
  } else {
    html_before <- html_after <- NULL
  }
  
  # ============================================
  # (1) Rnw -> LaTeX -> PDF
  # (2) Rmd -> MD -> (Pandoc) -> LaTeX -> PDF
  # ============================================
  
  if (to_pdf){
    
    out <- paste('\\includegraphics[', latex_options, ']{', image_file ,'}', sep = '')
    out <- paste(latex_before, out, latex_after, sep = '\n')
    
    if (use_knitr) {
      return(structure(out, class = c('knit_asis')))
    } else {
      cat(out)
      return(invisible())
    }
  }
  
  # ===========================================
  # (3) Rnw -> LaTeX -> (Pandoc) -> HTML
  # ===========================================
  
  if (!use_knitr && (identical(converter, 'pandoc') || use_pandoc)){
    out <- paste('\\includegraphics[', latex_options, ']{', image_file ,'}', sep = '')
    out <- paste(latex_before, out, latex_after, sep = '\n')
    
    cat(out)
    return(invisible())
  }

  # ===========================================
  # (4) Rnw -> LaTeX -> (tth/ttm) -> HTML
  # (5) Rmd -> MD -> (Pandoc) -> HTML
  # ===========================================
  
  alt <- if(!is.null(html_opts$alt)) sprintf('alt="%s"', html_opts$alt) else ''
  width <- if(!is.null(html_opts$width)) sprintf('width="%s"', html_opts$width) else ''
  out <- sprintf('<img src="%s" %s %s\ />', image_file, alt, width)
  out <- paste(html_before, out, html_after, sep = '\n')
  
  # (4)
  if (!use_knitr && (is.null(converter) || converter %in% c('ttm', 'tth'))) {
    out <- paste('\\begin{html}', out, '\\end{html}', sep = '\n')
    cat(out)
    return(invisible())
  }
  
  # (5)
  if (use_knitr) {
    return(structure(out, class = c('knit_asis')))
  }
  
  # ===========================================
  # (?) Don't know what to do (yet).
  # ===========================================
  
  cat("[[ Image Removed ]]")
  return(invisible())
}

rlogo2.Rmd

```{r, echo = FALSE, results = "hide"}
include_supplement("Rlogo.png",
dir = find.package("exams"), recursive = TRUE)
```

Question
========
What does the following logo stand for?

```{r, echo=FALSE}
include_graphics("Rlogo.png", 
                 html_opts = list(before = "<div style = 'text-align: center;'>",
                                  after = "</div>"),
                 latex_opts = list(before = "\\begin{center}", after = "\\end{center}"))
```


Answerlist
----------
* Programming language
* Letter in the alphabet
* Technology company
* Search engine
* Online retailer
* Pirate word

Solution
========

```{r, echo=FALSE}
include_graphics("Rlogo.png", 
                 html_opts = list(width = "50%", align = "center",
                                  before = "<div style = 'text-align: center;'>",
                                  after = "</div>"),
                 latex_opts = list(width = "0.5\\linewidth",
                                   before = "\\begin{center}", after = "\\end{center}"))
```

The logo stands for the R system for statistical computing and graphics (<http://www.R-project.org/>).

Answerlist
----------
* True. R is a programming language.
* False. Although R is (also) a letter in the alphabet, this is not what the logo represents.
* False. R is an open-source project, not a company.
* False. R is not a search engine.
* False. The R project does not sell anything.
* False. This is usually spelt _Arrr!_.


Meta-information
================
exname: R logo
extype: schoice
exsolution: 100000
exshuffle: 5