We present an uncalibrated projector-camera system in which the information displayed onto a planar screen can be interactively warped according to an arbitrary planar homography. The user interacts with the system through a laser pointer, whose displacements on the screen plane are captured by the camera, interpreted as mouse drags, and used to control the warping process. Applications of our interactive warping system encompass arbitrary (pan/tilt/screw) keystone correction, visualization of undistorted information for a user being in a general position with respect to the screen (including virtual anamorphosis as a special case), and self-shadow avoidance by a nearly-parallel projection.