Manually upgrading Three.js JSON geometry files from r42 to r55 - three.js

Question

I have some JSON files that define geometries, as required by r42 of Three.js's JSONLoader class. The files are version 2 of the format.
Is it feasible to manually update these files between versions?
The first obvious difference is that the file is no longer JavaScript, but actual JSON. This was easy to correct for. However the new format has a metadata section, and thirty minutes of experimentation with is isn't getting me anywhere.
I'm seeing problems because the Geometry object's material properties has an empty materials array. The resulting geometry has multiple parts with different materials, as seen in r42.
Does anyone know how I might manually tweak these .json files to work with r55?

Answer 1

I have no complete knowledge how the internals of the format have changed, but here's a couple of hints:
If you have the source object, the best way would be to re-export/convert. There should now also be more converters and exporters to use if your source format is obscure. If the source is unknown, some Googling might be worth it.
metadata section doesn't matter, it isn't used for anything in the loader.
There is no more Geometry.materials. Instead, JSONLoader's callback returns the loaded materials as a separate parameter to the callback. See Migration Guide (r52->r53) for more on that. In fact, the loader interface has changed also in r46.
git log of some example model files (searching for changes there could be your way forward if you really need to manually migrate) suggests that there might be e.g. UV flipping which would be difficult to fix manually but could be worked around in code. But first you'd need to get something to display on screen.

Answer 2

Try dragging the file into the editor, then do File/Export Geometry.

Answer 3

Here is a fix for drag and drop into the editor. Add this code before the drop event in index.html. I tested this in Chrome ( 24.0.1312.56 ), Safari and Firefox in OSX.
document.addEventListener("dragover", function(e) {
e.preventDefault();
});

Answer 4

#mrdoob's answer worked after a few patches to the editor (here and here.)
However it's worth noting that upgrading the files by hand in a text editor is possible, especially if you don't have any UV coords.
Earlier versions did not use JSON -- they were JavaScript files. The conversion is straightforward.
You can either ignore the metadata section, or else port it from the comments into an object.
If you do have UV coords, then they must be mapped differently (I believe an axis is flipped)