Rotating a square around the Z axis. To get the results you expect, send the rotate function angle parameters that are values between 0 and PI*2 (TWO_PI which is roughly 6.28). If you prefer to think about angles as degrees (0-360), you can use the radians() method to convert your values. For example: scale(radians(90)) is identical to the statement scale(PI/2).
Original Processing.org Example: Rotate