fromQuat.js

module.exports = fromQuat

/**
* Calculates a 3x3 matrix from the given quaternion
*
* @alias mat3.fromQuat
* @param {mat3} out mat3 receiving operation result
* @param {quat} q Quaternion to create matrix from
*
* @returns {mat3} out
*/
function fromQuat(out, q) {
  var x = q[0]
  var y = q[1]
  var z = q[2]
  var w = q[3]

  var x2 = x + x
  var y2 = y + y
  var z2 = z + z

  var xx = x * x2
  var yx = y * x2
  var yy = y * y2
  var zx = z * x2
  var zy = z * y2
  var zz = z * z2
  var wx = w * x2
  var wy = w * y2
  var wz = w * z2

  out[0] = 1 - yy - zz
  out[3] = yx - wz
  out[6] = zx + wy

  out[1] = yx + wz
  out[4] = 1 - xx - zz
  out[7] = zy - wx

  out[2] = zx - wy
  out[5] = zy + wx
  out[8] = 1 - xx - yy

  return out
}