Fluid sketches: continuous recognition and morphing of simple hand-drawn shapes

We describe a new sketching interface in which shape recognition and morphing are tightly coupled. Raw input strokes are continuously morphed into ideal geometric shapes, even before the pen is lifted. By means of smooth and continual shape transformations the user is apprised of recognition progress and the appearance of the final shape, yet always retains a sense of control over the process. At each time t the system uses the trajectory traced out thus far by the pen coupled with the current appearance of the time-varying shape to classify the sketch as one of several pre-defined basic shapes. The recognition operation is performed using shape-specific fits based on least-squares or relaxation, which are continuously updated as the user draws. We describe the time-dependent transformation of the sketch, beginning with the raw pen trajectory, using a family of first-order ordinary differential equations that depend on time and the current shape of the sketch. Using this formalism, we describe several possible behaviors that result by varying the relative significance of new and old portions of a stroke, changing the “viscosity” of the morph, and enforcing different end conditions. A preliminary user study suggests that the new interface is particularly effective for rapidly constructing diagrams consisting of simple shapes.