For anyone curious about this, I've updated the R scripts and detailed a 
bit more my workflow at https://tinyurl.com/ba-quarto-excalidraw (with 
example at https://github.com/baptiste/quarto-excalidraw/)

The retrieval of bounding boxes from Mathjax-produced SVGs is a slight 
complication, but it's optional (the boxes will refresh when re-rendered by 
Mathjax in Excalidraw).

Best,

baptiste

On Thursday, 26 January 2023 at 20:59:17 UTC+13 bapt a wrote:

> Hi,
>
> I'd like to extract all math equations from my lecture notes (and 
> potentially images too, at some stage) and produce a json file suitable for 
> Excalidraw, so that students could reorganise them, sketch notes 
> collaboratively, etc.:
>
> https://math.preview.excalidraw.com/
>
> [image: Screenshot 2023-01-26 at 20.34.57.png]
>
> (note that this is using a user-contributed extension*; the plain version 
> of Excalidraw does not support Mathjax or Asciimath). 
>
> From an equation like this in the source document (beamer tex):
>
> ```
> \[\begin{aligned}
> \nabla\cdot\mathbf{D}&= \rho_f\\
> \nabla\cdot\mathbf{B}&= 0\\
> \nabla\times\mathbf{E}&= -\frac{\partial\mathbf{B}}{\partial t}\\
> \nabla\times\mathbf{H}&= \frac{\partial\mathbf{D}}{\partial t} + 
> \mathbf{J}_f
> \end{aligned}\]
> ```
>
> the full json file suitable for import in Excalidraw looks like:
>
> ```
> {
> "type": "excalidraw",
> "version": 2,
> "source": "https://math.preview.excalidraw.com",
> "elements": [
> {
> "type": "text",
> "version": 104,
> "versionNonce": 669974443,
> "isDeleted": false,
> "id": "iL0y7olLhWzLKVTzIffR1",
> "fillStyle": "hachure",
> "strokeWidth": 1,
> "strokeStyle": "solid",
> "roughness": 1,
> "opacity": 100,
> "angle": 0,
> "x": 418,
> "y": -186,
> "strokeColor": "#000000",
> "backgroundColor": "transparent",
> "width": 202,
> "height": 169,
> "seed": 1021462275,
> "groupIds": [],
> "roundness": null,
> "boundElements": [],
> "updated": 1674718443076,
> "link": null,
> "locked": false,
> "subtype": "math",
> "customData": {
> "useTex": true,
> "mathOnly": true,
> "ariaLabel": "\\begin{aligned} \\nabla\\cdot\\mathbf{D}&= \\rho_f\\\\ \\
> nabla\\cdot\\mathbf{B}&= 0\\\\ \\nabla\\times\\mathbf{E}&= -\\frac{\\
> partial\\mathbf{B}}{\\partial t}\\\\ \\nabla\\times\\mathbf{H}&= \\frac{\\
> partial\\mathbf{D}}{\\partial t} + \\mathbf{J}_f \\end{aligned}"
> },
> "fontSize": 20,
> "fontFamily": 2,
> "text": "\\begin{aligned}\n\\nabla\\cdot\\mathbf{D}&= \\rho_f\\\\\n\\nabla
> \\cdot\\mathbf{B}&= 0\\\\\n\\nabla\\times\\mathbf{E}&= -\\frac{\\partial\\
> mathbf{B}}{\\partial t}\\\\\n\\nabla\\times\\mathbf{H}&= \\frac{\\partial
> \\mathbf{D}}{\\partial t} + \\mathbf{J}_f\n\\end{aligned}",
> "baseline": 91,
> "textAlign": "left",
> "verticalAlign": "top",
> "containerId": null,
> "originalText": "\\begin{aligned}\n\\nabla\\cdot\\mathbf{D}&= \\rho_f
> \\\\\n\\nabla\\cdot\\mathbf{B}&= 0\\\\\n\\nabla\\times\\mathbf{E}&= -\\
> frac{\\partial\\mathbf{B}}{\\partial t}\\\\\n\\nabla\\times\\mathbf{H}&= 
> \\frac{\\partial\\mathbf{D}}{\\partial t} + \\mathbf{J}_f\n\\end{aligned}"
> },
> {
> "type": "text",
> "version": 111,
> "versionNonce": 1291434347,
> "isDeleted": false,
> "id": "xzGehwC0igI1rh-jYddgb",
> "fillStyle": "hachure",
> "strokeWidth": 1,
> "strokeStyle": "solid",
> "roughness": 1,
> "opacity": 100,
> "angle": 0,
> "x": 754,
> "y": 32,
> "strokeColor": "#000000",
> "backgroundColor": "transparent",
> "width": 194,
> "height": 24,
> "seed": 315800227,
> "groupIds": [],
> "roundness": null,
> "boundElements": [],
> "updated": 1674718439209,
> "link": null,
> "locked": false,
> "subtype": "math",
> "customData": {
> "useTex": true,
> "mathOnly": true,
> "ariaLabel": "\\mathbf{F}= q\\left(\\mathbf{E}+ \\mathbf{v}\\times \\
> mathbf{B}\\right)"
> },
> "fontSize": 20,
> "fontFamily": 2,
> "text": "\\mathbf{F}= q\\left(\\mathbf{E}+ \\mathbf{v}\\times \\mathbf{B}
> \\right)",
> "baseline": 18,
> "textAlign": "left",
> "verticalAlign": "top",
> "containerId": null,
> "originalText": "\\mathbf{F}= q\\left(\\mathbf{E}+ \\mathbf{v}\\times \\
> mathbf{B}\\right)"
> }
> ],
> "appState": {
> "gridSize": null,
> "viewBackgroundColor": "#ffffff"
> },
> "files": {}
> }
> ```
>
> Obviously there isn't a one-to-one mapping between a typical input 
> document and what's possible or even desirable in a whiteboard context, but 
> for the limited scope of producing a bunch of equations automatically, it 
> would be very nice to have a pandoc writer. 
>
> At the moment I'm using a lua filter someone kindly contributed on this 
> mailing list, to simply extract all maths from an input file, 
>
> ```
> _ENV = pandoc
> local math_elements = List{}
> return {
> -- first document pass
> {Math = function (m) 
>
> local comment = "math start"
> math_elements:insert(comment)
> math_elements:insert(m)
> end},
> -- second document pass
> {Pandoc = function (_) return Pandoc(math_elements:map(Plain)) end},
> } 
> ```
>
> I then use a custom script (I wrote it in R since I'm more fluent in it) 
> to produce suitable json (
> https://github.com/baptiste/minixcali/blob/main/R/elements.R#L227)
>
> It works, but I feel this last step should really be implemented as a 
> custom Writer, especially if other people want to try this; unfortunately, 
> my lua skills are currently very limited. Any pointers / starter / 
> suggestions would be much appreciated!
>
> Best regards,
>
> baptiste
>
>
>
> *: fantastic work by user DanielJGeiger, 
> https://github.com/excalidraw/excalidraw/pull/6037
>

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