docs: @Pure
  	@SuppressWarnings("checkstyle:magicnumber")
  	public double getRotation() {
  		final double[] tmpScale = new double[3];
  		final double[] tmpRot = new double[9];
  		getScaleRotate2x2(tmpScale, tmpRot);
  		if (Math.signum(tmpRot[0]) != Math.signum(tmpRot[4])) {
  			// Sinuses are on the top-left to bottom-right diagonal
  			// -s   c   0
  			//  c   s   0
  			//  0   0   1
  			return Math.atan2(tmpRot[4], tmpRot[3]);
  		}
  		// Sinuses are on the top-right to bottom-left diagonal
  		//  c  -s  0
  		//  s   c  0
  		//  0   0  1
  		return Math.atan2(tmpRot[3], tmpRot[0]);
  	}