This week I wanted to do some tests with the cool project p5js and I wanted to use it from org-mode.

Regrettably, there is no package I could find that allows to use p5js in an org-mode document. What’s worse however is that apparently you can’t have two sketches in a single html file. Of course, to be fair, maybe this is my assessment of the library. As far as I can tell p5js can only deal with a single

<main></main>


tag. So I decided to let the good-old <iframe></iframe> save the day. But of course, I would like to simply write code and let org-mode handle the output automatically, i.e., I want to write

#+begin_src p5js
function setup() {
// ...
}
function draw() {
// ...
}
#+end_src


sit back and enjoy my interactive html document. So you have already seen the eye candy at the beginning of the document, and you can do everything that p5js can, which is trivially use WEBGL

where you can just write

#+begin_src p5js :height 200 :center t
function setup() {
createCanvas(500, 200, WEBGL);
}
function draw() {
background(255);
push();
normalMaterial();
rotateZ(frameCount * 0.01);
rotateX(frameCount * 0.01);
rotateY(frameCount * 0.01);
box(70, 70, 70);
pop();
}
#+end_src


export to html and get that nice rotating cube.

## Installing#

Below follows the implementation of the package in a literate programming fashion. If you are interested to see how easy it is to implement these kinds of packages just read on.

For the moment the development of this package happens over at https://github.com/alejandrogallo/ob-p5js.

As of [2022-10-14 Fri] I am going to submit the package to melpa, otherwise you can just simply copy the ob-p5js.el file where you can require it.

## Implementation#

The defaults for every src block are given by

(defcustom org-babel-default-header-args:p5js
'((:exports . "results")
(:results . "verbatim html replace value")
(:eval . "t")
(:width . "100%"))


where the most notable one is the :results, in that it creates an html export block.

The custom block arguments are the width and height for the iframe where the p5js is embedded in, and also a center boolean field in order to insert both the iframe and the main tag inside an html center element.

(defcustom org-babel-header-args:p5js
'((width . :any)
(height . :any)
(center . :any))


We need to include the script in the iframe environment, and you can customize where you want to get your p5js from. By default it points to the default one from the website

(defcustom p5js-src "https://cdn.jsdelivr.net/npm/p5@1.4.2/lib/p5.js"
"The source of p5js")


and I also give every iframe the class org-p5js by default, so that you can customize it via css or js.

(defcustom p5js-iframe-class "org-p5js"
"Default class for iframes containing a p5js sketch")


The body of the input for the iframe is a minimal html document containing the src script for p5js and yours:

(defun p5js--create-sketch-body (params body)
(format "
<html>
<script src=%S></script>
<script>
%s
</script>
<body>
%s
</body>
</html>
" p5js-src body (p5js--maybe-center params "<main></main>")))

(defun p5js--maybe-center (params body)
(if (alist-get :center params)
(format "<center>%s</center>" body)
body))


Now an important aspect arises, how do we embed the html document containing the sketch into the iframe. From all my testing I found that including the whole script as a base64 encoding hunk works best, so this is the approach I took

(defun p5js--create-iframe (params body &optional width height)
(let ((sketch (base64-encode-string (p5js--create-sketch-body params body))))
(p5js--maybe-center params
(format "<iframe class=\"%s\"
frameBorder='0'
%s
src=\"data:text/html;base64,%s\">
</iframe>"
p5js-iframe-class
(concat (if width
(format "width=\"%s\" " width)
"")
(if height
(format "height=\"%s\" " height)
""))
sketch))))


Last but not least, comes the part that tells org-babel how to execute p5js blocks, which entails simply defining a function prefixed by orb-babel-execute with the name of the src block.

(defun org-babel-execute:p5js (body params)
(let ((width (alist-get :width params))
(height (alist-get :height params)))
(p5js--create-iframe params body width height)))


And we want to inherit all the javascript goodness when working in p5js src blocks, this is

(define-derived-mode p5js-mode
js-mode "p5js"
"Major mode for p5js")

(provide 'ob-p5js)


## Conclusion#

And this is pretty much everything there is to it. I hope you have some more motivation to use it in your blog posts and provide interesting content to the community and to you.

For the future I would like to add some autocompletion or documentation checking for the mode, that would make the whole experience a little bit more painless.