add thumbnail file to 3mf output

[pca006132]

For some reason files without _rel/.rels cannot be imported into openscad. Seems like an issue with lib3mf, not sure if it is stated in the standard or not.

[t-paul]

I believe that comes from the OPC spec and is referenced in the 3MF spec in 2.1.1. 3D Parts and Payload Relationships.

This declares a mandatory relationship to the 3D Model part, so the minimal content of that file is a single entry like:

<?xml version="1.0" encoding="utf-8"?>
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
        <Relationship Type="http://schemas.microsoft.com/3dmanufacturing/2013/01/3dmodel" Target="/3D/3dmodel.model" Id="rel0" />
</Relationships>

[elalish]

Thanks, I was trying to figure out why nothing but Cura wanted to import our 3MFs. Apparently I forgot this in the intervening 8 years since I was writing that spec...

[elalish]

Huh, looks like Github is struggling today - our CI is mysteriously skipping jobs and my avatar icon is wrong. Hopefully it'll sort itself out...

[pca006132]

I think the skipped jobs are due to this PR being a draft PR when I initially opened it. Should now be fixed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6e1629d) 91.40% compared to head (2673d4c) 91.40%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #626   +/-   ##
=======================================
  Coverage   91.40%   91.40%           
=======================================
  Files          35       35           
  Lines        4512     4512           
=======================================
  Hits         4124     4124           
  Misses        388      388           

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[hrgdavor]

This should not work. If you look at the example in
https://github.com/hrgdavor/jscadui/blob/main/file-format/3mf-export/testGen.js

you need to take image from canvas form util like: cavassToPngA8

/** //example how to generate thumb from canvas and add it in fflate
const pngPreviewFile = new fflate.ZipPassThrough('Metadata/thumbnail.png');
zip.add(pngPreviewFile);
pngPreviewFile.push(cavassToPngA8(canvas), true);
*/
function cavassToPngA8(canvas) {
  let url = canvas.toDataURL('image/png')
  url = url.substring(url.indexOf(',') + 1)
  // strToU8 function from fflate
  return strToU8(url)
  // string to Uint8Array taken from stackoverflow, and should work in browser
  return new Uint8Array(
    atob(url)
      .split('')
      .map(c => c.charCodeAt(0)),
  )
}

notice 2 return return statements, use only one

[pca006132]

Ah, I need to check to see if it works, I didn't run the js, I just figured out we need a file in that location to make the 3mf recognizable from other programs.

Thanks for the reminder.