handmade.network » Forums » Why isn't there a decent 3D flat file format?
novus1044
10 posts
#20702 Why isn't there a decent 3D flat file format?
2 months, 1 week ago Edited by novus1044 on March 10, 2019, 5:36 p.m. Reason: Initial post

I wrote a parser for gltf files this weekend and found it extremely cumbersome to extract the information I needed to build the binary asset files. Instead of keeping the structure simple, aka flat, gltf creates a bunch of containers (scenes, nodes, accessors, buffer views, buffer, etc) with arrays of objects which contain references to other objects belonging to different containers. This makes it incredibly cumbersome to find out what buffer a mesh references because you need to traverse the nodes->mesh->accessor->buffer_view->buffer.

It got me wondering if there should be a simple flat file format that keeps all the information COLLADA and gltf scatter all over god's green earth into simple data records. The file would be a simple list of these records that loop for the number of meshes contained in the scene.

I know the above is very simplistic because you would need to account for much more data, animations for example, but if you have a simple layout then adding and more importantly parsing that data should be trivial.

There is also the issue of size but I would rather have a large file that is easy to manipulate than a tiny file that is a nightmare to code against.

Just a passing thought. Open to criticism/critiques.


mmozeiko
Mārtiņš Možeiko
1923 posts / 1 project
#20704 Why isn't there a decent 3D flat file format?
2 months, 1 week ago Edited by Mārtiņš Možeiko on March 10, 2019, 9:13 p.m.

https://xkcd.com/927/

Each use case is different. Different software have different requirements. Sure some are more terrible, some are more reasonable. But at the end any serious 3d game/engine converts input formats to their internal optimized formats, which is optimal for them, but maybe not for others. You want input formats (3d, textures, audio) to be in easy to make/distribute/modify file formats. Runtime format can be different (and they are). So it actually does not matter what input format is.
Guntha
30 posts
#20705 Why isn't there a decent 3D flat file format?
2 months, 1 week ago

I don't see how the xkcd strip is relatable here, gltf being the only standard format that claims to be a runtime format and not an interchange format; at the same time it is still bloated for most needs.

I made a gltf parser and I actually found that it is one of the most simple 3D scene formats to parse, even though it contains enough info to be imported into any 3D software without losing almost any information. But in the end, I still convert it to a flat format for a more straightforward loading process, with only the data I need.

For a simple yet complete runtime 3D file format, you could look into id's md5: http://tfc.duke.free.fr/coding/md5-specs-en.html You can probably find other simple formats in the repository of other open-source engines, each one probably having its own special needs.
mmozeiko
Mārtiņš Možeiko
1923 posts / 1 project
#20708 Why isn't there a decent 3D flat file format?
2 months, 1 week ago Edited by Mārtiņš Možeiko on March 11, 2019, 1:40 a.m.

xkcd was kind of answer to your "if there should be a simple flat file format that keeps all the information COLLADA and gltf scatter all over god's green earth into simple data records" text.

Sure, there is nothing wrong wanting something simpler that works for you and implementing it. But pretty much there always will be some extra feature/thing that does not work for somebody else. And then it won't be simpler for them to use this new format.

I'm not aware of any serious game engine that uses gltf as runtime format. I don't know exact history but afaik it is just a claim from khronos (about usability as runtime format). Who for some reason decided to push into web space and decided to create json-like text/binary format for loading into webgl. I guess xml-based collada was not good for them. So now we have json based format. What's next? Yaml? Protobuf?

I am aware of md5 format. I have written mdl/md2/md3/md5 loaders for fun. Those are real runtime formats for idTech engine. But again, what works for them won't work for everybody. Thus the xkcd comic strip.

Have you seen OpenGEX from Eric Lengyel? Not a binary/runtime format, but should be very usable as intermediate import format from 3d software. Here's an comparison with collada and gltf: https://opengex.org/comparison.html