Re: [Flightgear-devel] glTF object centers

[Fernando G. L. <fer...@fg...>]

On 12/2/25 13:52, Joshua Murphy wrote:
> Would the Blender add-on be a requirement for modellers? I know the need 
> for a Blender addon right now for .ac files cause some modellers some 
> headache - half of that is because of the AC3D format to be fair, but 
> the add-on also has to be updated and released at a cadence to keep up 
> with Blender releases (and sometimes you have to hunt for and install a 
> specific Blender version that the plugin supports).

Yes, the addon would be a requirement. Unfortunately keeping up with 
Blender versions is something we have to live with. We are lucky though 
that Blender became fairly standard and basically the only viable 
open-source option when it comes to doing serious 3D work. Imagine what 
a mess it would be to support our glTF extensions in other 3D packages 
as well.

> But if there's no other viable alternative it obviously sounds like a 
> good solution. Especially if it means (by the sounds of it) modellers 
> don't need to edit /quite/ as much XML, that's a *huge*​ win. Modellers 
> are used to needing to install/use an add-on anyways, so while it would 
> be nice to not have one, it would conceptually be the same thing as 
> before just with a different add-on.

The idea is to offload as much work as possible to the addon so we have 
control over versioning and breaking changes. A good example would be 
Effects: if we ever make a breaking change to an effect, aircraft devs 
won't care at all because the interface to the addon will be the same. 
We just need to increase the minimum required version, e.g. this 
aircraft was exported using the Blender addon for FG version 2025.1, but 
you are trying to use the aircraft in FG 2026.1, so you need to 
re-export your model. This re-exporting process can even be automated 
for aircraft in fgaddon.

Ideally we keep breaking changes to a minimum, but it's a fact of life 
that they exist and backwards compatibility is not guaranteed sometimes 
(just look at model-combined, for example). We should handle it the best 
we can and learn from the past.

> And this add-on would only have to do a tiny fraction of the work of the 
> current AC3D one. By the sounds of it, it would just be adding glTF 
> extension data, correct?

Yes, exactly. The heavy weight is already being pulled by the official 
Blender glTF extension.

-- 
Fernando