Interaction-based Rendering Optimization in Sketch- based User Interfaces

We describe two mechanisms, rendering task scheduling and the render cache, used to optimize graphics rendering in a scenegraph to provide continuous visual feedback and high interactivity in large-scale sketch-based user interfaces. We have implemented these mechanisms in SATIN, a toolkit to support development of sketch-based user interfaces. Our experiments with DENIM, an early-stage web site design tool built with SATIN, show that our changes significantly improve performance. INTRODUCTION Sketch-based user interfaces allow natural interaction by freeform sketching. They typically involve the semantic processing and rendering of many graphical objects during interaction, e.g., freeform strokes. One distinct feature of sketch-based user interfaces is continuous interaction, which requires continuous visual feedback. This usually involves complicated transformation of graphical objects and heavy rendering, which impedes the responsiveness of interactive systems. One useful way to organize graphical objects in a sketch-based user interface is to use a scenegraph [4]. SATIN [2] is a Java-based toolkit for developing sketch-based user interfaces, which employs a scenegraph to organize freeform graphical objects, such as strokes and patches. SATIN applications usually have large, complicated scenegraphs. For example, a typical web site design in DENIM [3], a web design application written with SATIN, usually has a scenegraph of