1. A method for controlling a computer system, comprising: detecting first and second touch inputs on a touch screen of the computer system; calculating a first centroid corresponding to the first touch input; calculating a second centroid corresponding to the second touch input; determining locations of the first and second touch inputs on the touch screen based on the first and second centroids, respectively; detecting a change in the determined locations of the first and second touch inputs; and performing an operation on the computer system in accordance with the detected change.