3D models in Unity, Tris or Quad ?

Hi,

I've always heard that you shouldn't make 3D models with quads to avoid problems,
but I also know that unity automatically converts quads to tris,
so I would like to know the opinion of someone more qualified in the field.

 

The usual advice these days is that you should use ONLY quads and nothing else if you plan to animate t he model and use subdivision surfaces. So I'm not sure where you got "shouldn't use quads" advice from. It is incorrect.

https://docs.unity3d.com/ScriptReference/MeshTopology.Quads.html

Technically Unity has ability to create quad-based meshes, though I'm not sure if meshes are imported as quads from external source, i.e. when you pull new assets into project.

You should always use quads when making characters, unless you go for low poly, because using quads makes modeling very convenient. Typical character topology looks like this:

Spoiler

And most likely there's not a single triangle on the whole model.

 

Everything you need to know here:
http://wiki.polycount.com/wiki/Polycount

Short answer: author your models with quads. Before baking it is good to make a triangulated version, and use that same triangulated version in engine to avoid discrepancy between engine auto-converting to triangles being different from what you baked.

Always make sure you keep the source file versions as quads so you can edit later easily. Quads is for humans. Triangles is for the computer.

 

While models are converted to trimeshes, the original quadmesh normals are retained. This is important as trimesh normals would not look correct on the kind of topology that are created from quadmesh->trimesh operation. That's another important thing to point out.

 

It's not that Unity converts them, it's that GPUs just draw triangles. Geometry can still be sent to the GPU as quads, and I think it even saves a little bandwidth, but when it comes time to draw, a quad is two tris.

If you twist a quad so it's not flat then you really ought to split it yourself, so that you control which way it's split, otherwise it may look different in engine. Other than that, quads are easier to manage and their normals behave more intuitively.