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We introduce Shadow Reaching, an interaction technique that makes use of a perspective projection applied to a shadow representation of a user. The technique was designed to facilitate manipulation over large distances and enhance understanding in collaborative settings. We describe three prototype implementations that illustrate the technique, examining the advantages of using shadows as an interaction metaphor to support single users and groups of collaborating users. Using these prototypes as a design probe, we discuss how the three components of the technique (sensing, modeling, and rendering) can be accomplished with real (physical) or computed (virtual) shadows, and the benefits and drawbacks of each approach.

Attribute gates are a new user interface element designed to address the problem of concurrently setting attributes and moving objects between territories on a digital tabletop. Motivated by the notion of task levels in activity theory, and crossing interfaces, attribute gates allow users to operationalize multiple subtasks in one smooth movement. We present two configurations of attribute gates; (1) grid gates which spatially distribute attribute values in a regular grid, and require users to draw trajectories through the attributes; (2) polar gates which distribute attribute values on segments of concentric rings, and require users to align segments when setting attribute combinations. The layout of both configurations was optimised based on targeting and steering laws derived from Fitts' Law. A study compared the use of attribute gates with traditional contextual menus. Users of attribute gates demonstrated both increased performance and higher mutual awareness.