index.js

var flatten = require('flatten-vertex-data')
var warned = false;

module.exports.attr = setAttribute
module.exports.index = setIndex

function setIndex (geometry, data, itemSize, dtype) {
  if (typeof itemSize !== 'number') itemSize = 1
  if (typeof dtype !== 'string') dtype = 'uint16'

  var isR69 = !geometry.index && typeof geometry.setIndex !== 'function'
  var attrib = isR69 ? geometry.getAttribute('index') : geometry.index
  var newAttrib = updateAttribute(attrib, data, itemSize, dtype)
  if (newAttrib) {
    if (isR69) geometry.addAttribute('index', newAttrib)
    else geometry.index = newAttrib
  }
}

function setAttribute (geometry, key, data, itemSize, dtype) {
  if (typeof itemSize !== 'number') itemSize = 3
  if (typeof dtype !== 'string') dtype = 'float32'
  if (Array.isArray(data) &&
    Array.isArray(data[0]) &&
    data[0].length !== itemSize) {
    throw new Error('Nested vertex array has unexpected size; expected ' +
      itemSize + ' but found ' + data[0].length)
  }

  var attrib = geometry.getAttribute(key)
  var newAttrib = updateAttribute(attrib, data, itemSize, dtype)
  if (newAttrib) {
    geometry.addAttribute(key, newAttrib)
  }
}

function updateAttribute (attrib, data, itemSize, dtype) {
  data = data || []
  if (!attrib || rebuildAttribute(attrib, data, itemSize)) {
    // create a new array with desired type
    data = flatten(data, dtype)

    var needsNewBuffer = attrib && typeof attrib.setArray !== 'function'
    if (!attrib || needsNewBuffer) {
      // We are on an old version of ThreeJS which can't
      // support growing / shrinking buffers, so we need
      // to build a new buffer
      if (needsNewBuffer && !warned) {
        warned = true
        console.warn([
          'A WebGL buffer is being updated with a new size or itemSize, ',
          'however this version of ThreeJS only supports fixed-size buffers.',
          '\nThe old buffer may still be kept in memory.\n',
          'To avoid memory leaks, it is recommended that you dispose ',
          'your geometries and create new ones, or update to ThreeJS r82 or newer.\n',
          'See here for discussion:\n',
          'https://github.com/mrdoob/three.js/pull/9631'
        ].join(''))
      }

      // Build a new attribute
      attrib = new THREE.BufferAttribute(data, itemSize);
    }

    attrib.itemSize = itemSize
    attrib.needsUpdate = true

    // New versions of ThreeJS suggest using setArray
    // to change the data. It will use bufferData internally,
    // so you can change the array size without any issues
    if (typeof attrib.setArray === 'function') {
      attrib.setArray(data)
    }

    return attrib
  } else {
    // copy data into the existing array
    flatten(data, attrib.array)
    attrib.needsUpdate = true
    return null
  }
}

// Test whether the attribute needs to be re-created,
// returns false if we can re-use it as-is.
function rebuildAttribute (attrib, data, itemSize) {
  if (attrib.itemSize !== itemSize) return true
  if (!attrib.array) return true
  var attribLength = attrib.array.length
  if (Array.isArray(data) && Array.isArray(data[0])) {
    // [ [ x, y, z ] ]
    return attribLength !== data.length * itemSize
  } else {
    // [ x, y, z ]
    return attribLength !== data.length
  }
  return false
}