Drawio engine for Knitr

Author: rchaput <rchaput.pro@gmail.com>

Description

This package adds a drawio engine to knitr, which can be used to automatically export draw.io diagrams into images from code chunks in RMarkdown documents.

Preview

Preview of the code chunk (in Rmd) and the PDF result

Installation

This package is only available on GitHub, you will therefore need to install remotes first:

# Install the remotes package to install packages directly from GitHub
install.packages("remotes")
# Now, install the knitrdrawio package from GitHub
remotes::install_github("rchaput/knitrdrawio")

Alternatively, you can also use devtools:

install.packages("devtools")
devtools::install_github("rchaput/knitrdrawio")

Note that this package requires the knitr package (which you should already have if you are writing Rmd documents).

It also requires to have installed on your system the draw.io binary.

On Docker (CI, etc.)

Draw.io requires a slightly different setup on headless environments (without a graphical server), such as Docker containers and in particular Continuous Integration workflows.

It is necessary to provide a “fake” graphical server in such environments; the easiest method is through the xvfb-run binary. On most Linux distributions, it can be obtained by installing the xvfb package through the distribution’s package manager (apt, rpm, …).

Alternatively, you may use the provided Docker image, which already includes all dependencies and can be directly used in your workflows. This image is automatically built against knitrdrawio’s latest release.

Please see the documentation for more details on how to use knitrdrawio in headless environments.

Usage

First, load the package in some code chunk, preferably at the beginning of your Rmd document:

```{r setup, include=FALSE}
library(knitr)
library(knitrdrawio)
```

After that, you can use draw.io diagrams in your Rmd document by using code chunks with the drawio engine:

```{drawio my-super-diag1, src="path/to/my-diag.drawio"}
```

Note that the code part of the chunk is empty (there is nothing after the header). You can customize the export process by using the chunk options. In the previous example, only the src option was specified: it is a mandatory option that sets the source diagram to export.

When the document is processed by knitr, the code chunk will be replaced by the resulting image.

Chunk options

Several chunk options are available to help you export the diagram exactly as you want.

Drawio-specific options

The following options are directly based on the draw.io available options (which you can get by using draw.io --help from a command-line interface):

Chunk option	draw.io equivalent	Description	Default value
src	[input file]	Path to the diagram to export	(Mandatory argument)
format	-f –format	Export format to use. Possible values are: pdf, png, jpg, svg, vsdx, xml	Depends on the document output format latex => pdf html => svg other => png
crop	–crop	Crop resulting image to diagram size	TRUE
transparent	-t –transparent	Set transparent background for PNG	FALSE
border	-b –border	Set border width around diagram	0
page.index	-p –page-index	Select a specific page	output format is an image => 1st page is selected otherwise => all pages are exported
page.range	-g –page-range	Similar to page.index, but selecting a range instead. For PDF only. Usage: “from..to”	NULL

Basic Knitr options

Some of the options defined in knitr can also be used, below is a list of a few important ones. A full list can be found in the documentation ; however, not all of them have been tested with knitrdrawio.

• label: A meaningful value should be given to this option, as it is used to name the resulting image. By default, knitr will set a label if not specified, but it might be harder to identify. Note that knitr allows to skip the label= part for this specific option, so in our examples you will only see {drawio <label>}.
• engine.path: By default, this package will try to find the draw.io executable in a sane default location, depending on your OS, but if the executable cannot be found, you can set this option to override it. Alternatively, you can set this option at a global level:

```{r setup}
knitr::opts_chunks$set(engine.path = list(
    drawio = "/path/to/your/draw.io"
))
```

• engine.opts: You can manually set additional command-line arguments that will be given to draw.io. Although most of the draw.io arguments should be handled by our engine’s options, this is useful if one of your use cases is not covered.
• eval: Set to FALSE to completely disable this chunk. Nothing will be executed, and the diagram will not be exported.
• include: Set to FALSE to only disable the inclusion of the result in the Rmd document. The chunk will still be executed, and the diagram exported as an image in your file system, but it will not appear in the document. This is useful if you want to automatically export diagrams, but manually include the images.
• cache: Set to TRUE to cache the chunk execution. The chunk will not be re-executed as long as the chunk options and the diagram source file’s checksum stay the same.
• fig.path: A prefix for the path to which the resulting image is written. Useful for, e.g., writing all figures to a figure/ directory. Non-existing directories are created.

Other options

• on.error: Controls what should knitrdrawio do when an error is encountered in draw.io:
  • stop (by default) abort, raise an informative error, and stop the document rendering.
  • skip raise an informative warning, and skip the current diagram.
  • continue: raise an informative warning, but let knitr try and include the diagram in the document. This method is proposed since draw.io does not explicitly signal an error, thus the error detection could report a false positive. In this case, the continue method can be used. However, it is not recommended in general: knitr will fail if the diagram can not be found!