'Internal keyboard event, don\'t override this.
Checks for the initial keydown of the basic testbed keys. Passes the
unused ones onto the test via the Keyboard() function.'

def _Keyboard_Event(self, key, down=True):

    if down:
        if (key == pygame.K_z):
            self.viewZoom = min((2 * self.viewZoom), 500.0)
        elif (key == pygame.K_x):
            self.viewZoom = max((0.9 * self.viewZoom), 0.02)
