close rstudio/bookdown#118: fig.cap works for HTML widgets now

DESCRIPTION

@@ -94,7 +94,7 @@ Suggests:
     rgl (>= 0.95.1201),
     codetools,
     rmarkdown,
-    htmlwidgets,
+    htmlwidgets (>= 0.7),
     webshot,
     tikzDevice (>= 0.10),
     png,

NEWS.md

@@ -8,6 +8,8 @@
 
 - added a `block2` engine for R Markdown documents as an alternative to the `block` engine; it should be faster and supports arbitrary Pandoc's Markdown syntax, but it is essentially a hack; note when the output format is LaTeX/PDF, you have to define `\let\BeginKnitrBlock\begin \let\EndKnitrBlock\end` in the LaTeX preamble
 
+- figure captions specified in the chunk option `fig.cap` are also applied to HTML widgets (thanks, @byzheng, https://github.com/rstudio/bookdown/issues/118)
+
 - added a `width` argument to `write_bib()` so long lines in bib entries can be wrapped
 
 - the inline syntax `` `r#code` `` is also supported besides `` `r code` ``; this can make sure the inline expression is not split when the line is wrapped (thanks, Dave Jarvis)

R/output.R

@@ -470,6 +470,11 @@ wrap.knit_asis = function(x, options, inline = FALSE) {
     # store metadata in an object named of the form .hash_meta when cache=TRUE
     if (length(m) && options$cache == 3)
       assign(cache_meta_name(options$hash), m, envir = knit_global())
+    if (inherits(x, 'knit_asis_htmlwidget')) {
+      options$fig.cur = plot_counter()
+      options = reduce_plot_opts(options)
+      return(add_html_caption(options, x))
+    }
   }
   x = as.character(x)
   if (!out_format('latex') || inline) return(x)
@@ -595,15 +600,18 @@ wrap.html_screenshot = function(x, options = opts_chunk$get(), inline = FALSE) {
 wrap.knit_embed_url = function(x, options = opts_chunk$get(), inline = FALSE) {
   options$fig.cur = plot_counter()
   options = reduce_plot_opts(options)
-  iframe = sprintf(
+  add_html_caption(options, sprintf(
     '<iframe src="%s" width="%s" height="%s"></iframe>',
     escape_html(x$url), options$out.width %n% '100%', x$height %n% '400px'
-  )
+  ))
+}
+
+add_html_caption = function(options, code) {
   cap = .img.cap(options)
-  if (cap == '') return(iframe)
+  if (cap == '') return(code)
   sprintf(
     '<div class="figure"%s>\n%s\n<p class="caption">%s</p>\n</div>',
-    css_text_align(options$fig.align), iframe, cap
+    css_text_align(options$fig.align), code, cap
   )
 }
 

R/utils.R

@@ -708,7 +708,13 @@ current_input = function(dir = FALSE) {
 default_handlers = evaluate:::default_output_handler
 # change the value handler in evaluate default handlers
 knit_handlers = function(fun, options) {
-  if (!is.function(fun)) fun = knit_print
+  if (!is.function(fun)) fun = function(x, ...) {
+    res = knit_print(x, ...)
+    # indicate the htmlwidget result with a special class so we can attach
+    # the figure caption to it later in wrap.knit_asis
+    if (inherits(x, 'htmlwidget')) class(res) = c(class(res), 'knit_asis_htmlwidget')
+    res
+  }
   if (length(formals(fun)) < 2)
     stop("the chunk option 'render' must be a function of the form ",
          "function(x, options) or function(x, ...)")