# Three Subdivide

This modifier uses the Loop (Charles Loop, 1987) subdivision surface algorithm to smooth modern three.js BufferGeometry.

## Background

At one point, three.js included a subdivision surface modifier in the extended examples, it was removed in r125. This modifier was originally based on the Catmull-Clark algorithm, which works best for geometry with convex coplanar n-gon faces. In three.js r60 the modifier was changed to use the Loop algorithm, which was designed to work better with triangle based meshes.

The Loop algorithm, however, doesn’t always provide uniform results as the vertices are skewed toward the most used vertex positions. A triangle box (like BoxGeometry for example) will favor the corners. To alleviate this issue, this implementation includes an initial pass to split coplanar faces at their shared edges. It starts by splitting along the longest shared edge first, and then from that midpoint it splits to any remaining coplanar shared edges. This can be disabled by passing ‘split’ as false.

Also by default, this implementation inserts new UV coordinates, but does not average them using the Loop algorithm. In some cases (usually in round-ish geometries) this will produce undesired results, a noticeable tearing will occur. In such cases, try passing ‘uvSmooth’ as true to enable UV averaging.

## Apply

LoopSubdivision.apply(bufferGeometry, iterations = 1, split = true, uvSmooth = false, flatOnly = false, maxTriangles = Infinity)

• bufferGeometry : BufferGeometry – existing three.js BufferGeometry object.
• iterations : Int (optional) – total passes of subdivision to apply, generally between 1 to 5.
• split : Boolean (optional) – split coplanar faces at their shared edges before subdividing?
• uvSmooth : Boolean (optional) – smooth UV coordinates during subdivision?
• flatOnly : Boolean (optioanl) – subdivide triangles but do not apply smoothing?
• maxTriangles : Number (optional) – limits subdivision to meshes with less than this number of triangles.

NOTE: This modifier converts geometry to non-indexed before the subdivision algorithm is applied. If desired, you can use BufferGeometryUtils.mergeVertices to re-index geometry.

## Usage

To create subdivided geometry, use the static function apply(). The following code creates a cube with smoothed geometry and adds it to a three.js Scene.

import * as THREE from 'three';
import { LoopSubdivision } from 'LoopSubdivision.js';

const geometry = LoopSubdivision.apply(new THREE.BoxGeometry());

const material = new THREE.MeshNormalMaterial();
const mesh = new THREE.Mesh(geometry, material);

const scene = new THREE.Scene();

Subdivide is released under the terms of the MIT license, so it is free to use in your free or commercial projects.

Copyright (c) 2022 Stephens Nunnally <@stevinz>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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