[omgbdhjk] Panning and rotating rectangle

Tile a rectangular image, then place a rectangular viewport the same size as the image on the plane.  No matter the offset or orientation, exactly the entire image will be visible, though cut up.  (Is this fact interesting or obvious?)  Slide and turn the viewport around to offer different views of the same image.  Easiest is irrational slope and constant irrational rate of rotation, so the viewport will never repeat.