identifying an orientation of a mobile telephone;

presenting a computer simulation on the mobile telephone;

transforming an image of a player of the computer simulation based at least in part on the orientation, the image being from a camera on the mobile telephone, the transforming comprising, for purposes of body orientation rendering, keeping gravity pointing down (toward the center of the Earth) no matter what the orientation of the mobile telephone is such that the player is tracked with a gravity-correct image that is provided to the computer simulation; and

controlling execution of the computer simulation based at least in part on the orientation.