A portable game system that uses polygon graphics to generate a 3-D player character, or body part such as a hand, moving through a 3-D simulated game space for display on an LCD screen in the portable game system. Overlaying an LCD screen is a touch screen that senses the variable locations of a physical object, such as the player's finger, moving on the touchscreen so that motions of the displayed player character follow the motions of the touching object. Whenever the player character collides with a second object, motion of the player character deviates from the touchscreen-controlled motion in response to the collision.