Geometry's fromBufferGeometry() should clean vertices and colors

Geometry’s fromBufferGeometry() exports duplicated vertices and colors.

Code to reproduce:

var box = new THREE.BoxGeometry(1,1,1);
var bufferBox = new THREE.BufferGeometry();
bufferBox.fromGeometry(box);

var newBox = new THREE.Geometry();
newBox.fromBufferGeometry(bufferBox);

Result: box : {vertices: Array(8), colors: Array(0)} newBox : {vertices: Array(36), colors: Array(36)}

If you see useful, we have written a basic method to remove the vertices and fix the vertex index in the faces:

function clearDuplicateVertices(geometry) {
        //store the vertex index changes
        var data = [];
        var vertices = [];
        var faces = [];

        //vertices
        for (var v = 0; v < geometry.vertices.length; v++) {
            var vertex = geometry.vertices[v];

            //see if we have that vertex already
            var newIndex = -1;
            for (var i = 0; i < vertices.length; i++) {
                if (vertices[i].equals(vertex))
                {
                    newIndex = i;
                    break;
                }
            }

            if (newIndex > -1)
            {
                data.push({oldIndex: v, newIndex: newIndex});
            } else
            {
                vertices.push(vertex);
                data.push({oldIndex: v, newIndex: vertices.length - 1});
            }
        }

        //faces
        for (var f = 0; f < geometry.faces.length; f++) {
            var currentFace = geometry.faces[f];

            var a = currentFace.a;
            var b = currentFace.b;
            var c = currentFace.c;
            for (var i = 0; i < data.length; i++) {
                var currentData = data[i];

                if (a === currentData.oldIndex) {
                    a = currentData.newIndex;
                }

                if (b === currentData.oldIndex) {
                    b = currentData.newIndex;
                }

                if (c === currentData.oldIndex) {
                    c = currentData.newIndex;
                }
            }
            faces.push(new THREE.Face3(a, b, c));
        }

        //copy
        var geo = new THREE.Geometry();
        geo.vertices = vertices;
        geo.faces = faces;
        geo.computeFaceNormals();
        return geo;
    }

Three.js version

• r96

[Mugen87]

BufferGeometry.fromGeometry() always creates a non-indexed BufferGeometry. Read #11776 from more information.

It’s more interesting to investigate if it’s possible to avoid the creation of a color attribute. This happens in all cases because of this code in DirectGeometry:

https://github.com/mrdoob/three.js/blob/8b6a60ed44d017a364aa66d101789c2231c88954/src/core/DirectGeometry.js#L177-L187

[Mugen87]

Okay, I’m fine with this decision.

Furthermore, vertex perturbations can have a significant impact on models defined on a small scale.

It’s not complicated to scale the epsilon or precision value based on the min/max values of the geometry. Many algorithms in the area computational geometry do this and produce proper results. A fix for this in .mergeVertices() is doable.