[Bf-committers] Proposal: Export extensions for better integration with game engines.

[Juan Linietsky]

We can probably pull request this functionality into Blender ourselves, or
at least generate a detailed proposal but for this I would like to see if
Blender contributors can agree that this is something wanted and how it
would be wanted.

Best

Juan


On Thu, Mar 4, 2021 at 8:43 PM Juan Linietsky <reduzio at gmail.com> wrote:

> As I mentioned before, the problem with using properties, even if hidden,
> is that having this information persistent serves no purpose.
> I understand that Blender can save it (with an option), but there is no
> point in generating this information at any other time than saving the
> exported scene..
>
> This is why, the Ideal API use case for this is every exporter calling
> some sort of new internal function that asks export metadata plugins to
> generate this information, at export time and during the export process.
>
> I am a bit unfamiliar nowadays with Blender internals, but I can ask other
> Godot contributors to create a more specific proposal for this.
>
> Juan
>
>
> On Thu, Mar 4, 2021 at 6:33 PM Toni Alatalo <toni at playsign.net> wrote:
>
>> Fair points, thanks. BTW if there is an issue on the web or something for
>> this, am happy to study more there and maybe have extended discussions,
>> don't want to flood the list with learning the basics about this.
>>
>> I was thinking, that if you need additional meta-data, you could maybe
>> have hidden custom properties, if they are for the export code only, and
>> not meant to be user facing. I don't know if Blender supports hiding custom
>> props nor whether I'd make sense. Maybe would work for the UUIDs for
>> example.
>>
>> Now when you say that it's at export time, and with data that already
>> exists in Blender, I fail to see why an exporter can't do what you want
>> then.
>>
>> So what is it that you are proposing exactly? Some kind of additional API
>> to Blender that would support getting info nicely for exporters?
>>
>> Exporters already are 'metadata export plugins' and can do whatever is
>> necessary AFAIK. Of course if there is something missing in the API that
>> exporters need it's possible to add.
>>
>> Anyway I think those were my points and I go silent here now to not spam
>> with clueless questions :)
>>
>> -Toni
>>
>>
>>
>> On Thu, Mar 4, 2021 at 11:24 PM Juan Linietsky <reduzio at gmail.com> wrote:
>>
>>> So how is this not custom properties?
>>>>
>>>
>>> I don't think custom properties are the best for this use-case scenario,
>>> for the following reasons:
>>>
>>> * You need to generate this data *on export*. As an example, if you
>>> edited the material nodes in Blender, you would only want to generate a
>>> target engine shader at the time you are exporting the file, as this can be
>>> a costly process. Doing it at any other time is unnecessary and inefficient.
>>> * Custom properties are meant to be *user-facing*, there is zero
>>> benefit in users seeing data meant *for the exporter*.
>>> * Again remember, the use of this is to take data that *already exists
>>> in blender* (not that was created by the user) and send it to a game
>>> engine. It's a different use case (and hence, feature).
>>>
>>> Juan
>>>
>>>
>>> On Thu, Mar 4, 2021 at 3:53 PM Toni Alatalo via Bf-committers <
>>> bf-committers at blender.org> wrote:
>>>
>>>> So how is this not custom properties?
>>>>
>>>> https://docs.blender.org/manual/en/latest/files/data_blocks.html#custom-properties
>>>>
>>>> On Thu, Mar 4, 2021 at 8:05 PM Juan Linietsky via Bf-committers <
>>>> bf-committers at blender.org> wrote:
>>>>
>>>> > Hi Everyone!
>>>> >
>>>> >    Most exporters are working fantastic nowadays in Blender, so on the
>>>> > Godot Engine side, we are trying to figure how better to improve our
>>>> > experience to users when going back and forth between Blender and
>>>> Godot.
>>>> >
>>>> >    So, this proposal consists on a very (pre-discussed) list of
>>>> topics that
>>>> > we would be glad to work together in ensuring Blender can support
>>>> these
>>>> > somehow (which should hopefully happen with minimal effort).
>>>> >
>>>> >    The main topic is the ability for Blender to have a "Metadata
>>>> Export"
>>>> > plugin. This means, that at the time of export,and for each object
>>>> exported
>>>> > (node, material, skeleton, mesh, etc) Blender should be able to ask
>>>> for
>>>> > "metadata" to the export plugins. Export plugins can then return
>>>> generic
>>>> > metadata (Strings or what you believe is best) to embed in exported
>>>> scenes.
>>>> >
>>>> >   Here are use cases where these type of plugins would be very useful:
>>>> >
>>>> > * *UUID exporting*: When we import a scene on the game engine side,
>>>> we can
>>>> > only track objects by name. Blender uses unique names for objects, but
>>>> > artists will often rename them, causing data added on the engine side
>>>> (such
>>>> > as overriding materials, changing positions, setting children nodes
>>>> to,
>>>> > etc) to be lost.  Ideally, Blender should be able to assign UUIDs to
>>>> every
>>>> > object at the time of creation (does not need to be global, can be per
>>>> > blender file). If not desired to be core in Blender, then the add-on
>>>> should
>>>> > be able to do this somehow.
>>>> > * *Material Exporting:* Exporting materials is very limited in any
>>>> format.
>>>> > Users often just want to model directly on Blender, set up the
>>>> materials
>>>> > with nodes, and then expect them to work in the engine. To solve
>>>> this, we
>>>> > originally wrote a direct Blender -> Godot exporter, but this is very
>>>> > difficult to maintain where the main thing we need is just materials.
>>>> On
>>>> > export, we convert Blender Materials to Godot Shaders, so they work
>>>> > automatically on the engine. If this can be saved as metadata in
>>>> > GLTF/DAE/FBX, it's much easier for us to maintain.
>>>> > * *Extra parameters for lights and cameras*: Sometimes, we want more
>>>> > parameters exported from lights, cameras, etc. in order to make sure
>>>> scenes
>>>> > just work.
>>>> > * *Extra types of objects:* Godot supports Splines, IK, Physics and
>>>> many
>>>> > other types of objects that blender supports, but that no export
>>>> format
>>>> > does. Being able to export those as metadata in the exporter would be
>>>> very
>>>> > useful. As an example, when making a racing game, exporting a Spline
>>>> used
>>>> > to create a racetrack helps make a better AI.
>>>> >
>>>> > So, all this could be done if exporters polled export metadata
>>>> plugins for
>>>> > metadata at the time of export (so we ensure we convert from the most
>>>> > recent version of the object) on any object, then added it in the
>>>> exported
>>>> > data. This is a minimal non-invasive change in Blender exporters, but
>>>> adds
>>>> > huge flexibility to engine export.
>>>> >
>>>> > Best
>>>> >
>>>> > Juan
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