Function fromMat3

docs/demo/spritejs.worker.esm.js:4310–4342

* Creates a quaternion from the given 3x3 rotation matrix. * * NOTE: The resultant quaternion is not normalized, so you should be sure * to renormalize the quaternion yourself where necessary. * * @param {quat} out the receiving quaternion * @param {ReadonlyMat3} m rotation matrix * @r

(out, m)

 */

function fromMat3(out, m) {
  // Algorithm in Ken Shoemake's article in 1987 SIGGRAPH course notes
  // article "Quaternion Calculus and Fast Animation".
  var fTrace = m[0] + m[4] + m[8];
  var fRoot;

  if (fTrace > 0.0) {
    // |w| > 1/2, may as well choose w > 1/2
    fRoot = Math.sqrt(fTrace + 1.0); // 2w

    out[3] = 0.5 * fRoot;
    fRoot = 0.5 / fRoot; // 1/(4w)

    out[0] = (m[5] - m[7]) * fRoot;
    out[1] = (m[6] - m[2]) * fRoot;
    out[2] = (m[1] - m[3]) * fRoot;
  } else {
    // |w| <= 1/2
    var i = 0;
    if (m[4] > m[0]) i = 1;
    if (m[8] > m[i * 3 + i]) i = 2;
    var j = (i + 1) % 3;
    var k = (i + 2) % 3;
    fRoot = Math.sqrt(m[i * 3 + i] - m[j * 3 + j] - m[k * 3 + k] + 1.0);
    out[i] = 0.5 * fRoot;
    fRoot = 0.5 / fRoot;
    out[3] = (m[j * 3 + k] - m[k * 3 + j]) * fRoot;
    out[j] = (m[j * 3 + i] + m[i * 3 + j]) * fRoot;
    out[k] = (m[k * 3 + i] + m[i * 3 + k]) * fRoot;
  }

  return out;
}
/**
 * Creates a quaternion from the given euler angle x, y, z.
 *