function rotateX(m, angleInRadians, dst) {
  dst = dst || new MatType(16);
  var m10 = m[4];
  var m11 = m[5];
  var m12 = m[6];
  var m13 = m[7];
  var m20 = m[8];
  var m21 = m[9];
  var m22 = m[10];
  var m23 = m[11];
  var c = Math.cos(angleInRadians);
  var s = Math.sin(angleInRadians);
  dst[4] = c * m10 + s * m20;
  dst[5] = c * m11 + s * m21;
  dst[6] = c * m12 + s * m22;
  dst[7] = c * m13 + s * m23;
  dst[8] = c * m20 - s * m10;
  dst[9] = c * m21 - s * m11;
  dst[10] = c * m22 - s * m12;
  dst[11] = c * m23 - s * m13;

  if (m !== dst) {
    dst[0] = m[0];
    dst[1] = m[1];
    dst[2] = m[2];
    dst[3] = m[3];
    dst[12] = m[12];
    dst[13] = m[13];
    dst[14] = m[14];
    dst[15] = m[15];
  }

  return dst;
}
Rotates the given 4-by-4 matrix around the x-axis by the given
angle.
@param {module:twgl/m4.Mat4} m The matrix.
@param {number} angleInRadians The angle by which to rotate (in radians).
@param {module:twgl/m4.Mat4} [dst] matrix to hold result. If not passed a new one is created.
@return {module:twgl/m4.Mat4} The rotated matrix.
@memberOf module:twgl/m4