Rotate mesh points towards a direction vector with stack-gl / regl

pointTowards

// inspired by toxiclibs
// https://bitbucket.org/postspectacular/toxiclibs/src/44d9932dbc9f9c69a170643e2d459f449562b750/src.core/toxi/geom/mesh/TriangleMesh.java?at=default&fileviewer=file-view-default#TriangleMesh.java-703

const vec3 = require('gl-vec3')
const mat3 = require('gl-mat3')
const mat4 = require('gl-mat4')
const quat = require('gl-quat')

function transform(matrix, v) {
  const temp = mat3.create()
  const width = 4
  for (let i = 0; i < width; i++) {
    const matrixGet = (x, y) => matrix[ y + (x * width) ]
    temp[i] = v[0] * matrixGet(i, 0) + v[1] * matrixGet(i, 1) + v[2] * matrixGet(i, 2) + matrixGet(i, 3)
  }
  const out = [ temp[0], temp[1], temp[2] ]
    .map(x => x * (1.0 / temp[3]))
  return out
}

const Z_AXIS = [0, 0, 1]
function pointTowards(positions, dir, forward) {
  forward = forward || Z_AXIS
  dir = vec3.normalize([], dir)
  forward = vec3.normalize([], forward)
  const ret = positions.map(point => {
    const q = quat.rotationTo(quat.create(), dir, forward)
    const matFromQuat = mat4.fromQuat(mat4.create(), q)
    const out = transform(matFromQuat, point)
    return out
  })
  return ret
}

module.exports = pointTowards