1. An electronic device comprising: a display screen configured for displaying images; a touch sensor configured to detect user input in a sensing region, wherein said sensing region overlaps with an active area of said display screen; a host processing system; and a touch screen control system comprising: a memory configured for holding rules; and control circuitry configured for: operating according to a first set of rules held in said memory; in response to receiving an indication from said host processing system, switching from operating according to said first set of rules to operating according to a second set of rules; and operating according to said second set of rules; said control circuitry comprising: a blended image generator for autonomously generating a blended image by blending a primary image held in said memory and a secondary image held in said memory in response to said detected user input; and a display screen updater for autonomously updating said display screen with said blended image, wherein said display screen is updated at a higher rate when updated autonomously by said display screen updater than when directed by said host processing system, and wherein said autonomously updating said display screen by said display screen updater reduces processing of said host processing system.