Two-Handed Image Navigation in Fran

The idea of image navigation is to allow a user to explore a complex image such as a map, moving smoothly between different locations, scales, and orientations. Single-handed input (e.g., with a single mouse) requires the user to change “input modes”, interrupting the flow of the user’s main task. Two-handed input eliminates the need for conscious mode changes, freeing the user to concentrate on the navigation task. The implementation described in this paper is written in Haskell, using the Fran interactive animation library. While the C++ program that inspired this exercise is quite long and complex, the Fran version is short, modular and we feel captures the essence of the behavior being modeled.