Three.js - What is PlaneBufferGeometry

PlaneBufferGeometry is a low memory alternative for PlaneGeometry. the object itself differs in a lot of ways. for instance, the vertices are located in PlaneBufferGeometry are located in PlaneBufferGeometry.attributes.position instead of PlaneGeometry.vertices

you can take a quick look in the browser console to figure out more differences, but as far as i understand, since the vertices are usually spaced on a uniform distance (X and Y) from each other, only the heights (Z) need to be given to position a vertex.

The main differences are between Geometry and BufferGeometry.

Geometry is a "user-friendly", object-oriented data structure, whereas BufferGeometry is a data structure that maps more directly to how the data is used in the shader program. BufferGeometry is faster and requires less memory, but Geometry is in some ways more flexible, and certain operations can be done with greater ease.

I have very little experience with Geometry, as I have found that BufferGeometry does the job in most cases. It is useful to learn, and work with, the actual data structures that are used by the shaders.

In the case of a PlaneBufferGeometry, you can access the vertex positions like this:

let pos = geometry.getAttribute("position");
let pa = pos.array;

Then set z values like this:

var hVerts = geometry.heightSegments + 1;
var wVerts = geometry.widthSegments + 1;
for (let j = 0; j < hVerts; j++) {
    for (let i = 0; i < wVerts; i++) {
                            //+0 is x, +1 is y.
        pa[3*(j*wVerts+i)+2] = Math.random();
    }
}
pos.needsUpdate = true;
geometry.computeVertexNormals();

Randomness is just an example. You could also (another e.g.) plot a function of x,y, if you let x = pa[3*(j*wVerts+i)]; and let y = pa[3*(j*wVerts+i)+1]; in the inner loop. For a small performance benefit in the PlaneBufferGeometry case, let y = (0.5-j/(hVerts-1))*geometry.height in the outer loop instead.

geometry.computeVertexNormals(); is recommended if your material uses normals and you haven't calculated more accurate normals analytically. If you don't supply or compute normals, the material will use the default plane normals which all point straight out of the original plane.

Note that the number of vertices along a dimension is one more than the number of segments along the same dimension.

Note also that (counterintuitively) the y values are flipped with respect to the j indices: vertices.push( x, - y, 0 ); (source)