Trimesh Class

In which you abstract away the complexities of managing a 3D model.

Triangular meshes are made of several arrays upon which you need to execute various operations. They warrant an abstraction that draws together the otherwise scattered state and behaviors into a single entity. You need a Trimesh class.

A possible interface for the Trimesh class is described below. It assumes that your mesh uses indexed geometry.

State

The Trimesh class binds together at least these three arrays.

Positions. The class must maintain a list of vertex positions. You are advised to store them as a list of Vector3 or Vector4 instead of as a flat array or an array of arrays. By storing them as vectors, you can perform vector operations on the positions.
Normals. If you plan on shading the mesh, then each vertex needs a normal. As with with the positions, you are advised to store these as a list of Vector3 or Vector4.
Indices. You need to know how the triangles are connected together. To ease operations that you'll add later, you are advised to store the triangles as an array of arrays, with each inner array representing a single triangle. For example,
```
[
  [0, 1, 3], // triangle 0
  [0, 3, 2], // triangle 1
  // ...
]
```

There are some other pieces of state you might consider storing. Perhaps you need color information like albedo or shininess. These could be uniform across the mesh or defined on a per-vertex basis. Perhaps you want to track the number of vertices and faces in properties instead of computing them from the arrays.

Behaviors

At this point in the development of your graphics library, your class needs only a few behaviors.

Constructor

The constructor receives the positions, normals, and indices and hangs on to them for later use.

Flat Getters

The GPU cares little for your abstraction. It wants flat arrays of raw numbers to put in the VBOs. Each of your arrays needs a getter that returns a flattened representation of the array. Consider using JavaScript's flatMap and flat methods to do most of the labor.

fromObj

The OBJ parser that you write needs a home. If JavaScript supported overloading, you could add a second constructor that took in the OBJ string. But it doesn't. That's okay, because you can write a static method named fromObj that receives the text and returns a Trimesh instance. Such a method is sometimes is called a named constructor.