fansi (version 0.4.0)

set_knit_hooks: Set an Output Hook to Display ANSI CSI SGR in Rmarkdown

Description

This is a convenience function designed for use within an rmarkdown document. It overrides the knitr output hooks by using knitr::knit_hooks$set. It replaces the hooks with ones that convert ANSI CSI SGR sequences into HTML. In addition to replacing the hook functions, this will output a <STYLE> HTML block to stdout. These two actions are side effects as a result of which R chunks in the rmarkdown document that contain ANSI CSI SGR are shown in their HTML equivalent form.

Usage

set_knit_hooks(hooks, which = "output", proc.fun = function(x, class)
  html_code_block(sgr_to_html(html_esc(x)), class = class),
  class = sprintf("fansi fansi-%s", which),
  style = getOption("fansi.css"), .test = FALSE)

Arguments

hooks

list, this should the be knitr::knit_hooks object; we require you pass this to avoid a run-time dependency on knitr.

which

character vector with the names of the hooks that should be replaced, defaults to 'output', but can also contain values 'message', 'warning', and 'error'.

proc.fun

function that will be applied to output that contains ANSI CSI SGR sequences. Should accept parameters x and class, where x is the output, and class is the CSS class that should be applied to the <PRE><CODE> blocks the output will be placed in.

class

character the CSS class to give the output chunks. Each type of output chunk specified in which will be matched position-wise to the classes specified here. This vector should be the same length as which.

style

character a vector of CSS styles; these will be output inside HTML <STYLE> tags as a side effect. The default value is designed to ensure that there is no visible gap in background color with lines with height 1.5 (as is the default setting in rmarkdown documents v1.1).

.test

TRUE or FALSE, for internal testing use only.

Value

named list with the prior output hooks for each of which.

Details

The replacement hook function tests for the presence of ANSI CSI SGR sequences in chunk output with has_sgr, and if it is detected then processes it with the user provided proc.fun. Chunks that do not contain ANSI CSI SGR are passed off to the previously set hook function. The default proc.fun will run the output through html_esc, sgr_to_html, and finally html_code_block.

If you require more control than this function provides you can set the knitr hooks manually with knitr::knit_hooks$set.

See Also

has_sgr, sgr_to_html, html_esc, html_code_block, knitr output hooks, embedding CSS in Rmd.

Examples

# NOT RUN {
## The following should be done within an `rmarkdown` document chunk with
## chunk option `results` set to 'asis' and the chunk option `comment` set
## to ''.

```{r comment="", results='asis', echo=FALSE}
## Change the "output" hook to handle ANSI CSI SGR

old.hooks <- set_knit_hooks(knitr::knit_hooks)

## Do the same with the warning, error, and message, and add styles for
## them (alternatively we could have done output as part of this call too)

styles <- c(
  getOption('fansi.style'),  # default style
  "PRE.fansi CODE {background-color: transparent;}",
  "PRE.fansi-error {background-color: #DD5555;}",
  "PRE.fansi-warning {background-color: #DDDD55;}",
  "PRE.fansi-message {background-color: #EEEEEE;}"
)
old.hooks <- c(
  old.hooks,
  fansi::set_knit_hooks(
    knitr::knit_hooks,
    which=c('warning', 'error', 'message'),
    style=styles
) )
```
## You may restore old hooks with the following chunk

## Restore Hooks
```{r}
do.call(knitr::knit_hooks$set, old.hooks)
```
# }