Layered penumbrae: an effective 3D feedback technique

Shadows serve as effective cues for a user to recognize spatial relations among objects in 3D space. However simple shadows typically used in 3D interfaces are often insufficient for the purpose, and rendering of shadows with real penumbra are not only too costly for interactive interfaces, but also do not enhance their capabilities as spatial cues. Our proposal, layered penumbra is a new interactive feedback technique that overcomes these deficiencies; it positively enhances the user´s perception of spatial relations, looks natural to the eye, and furthermore can be rendered fast enough for interactive 3D interfaces. The layered penumbra has three layers (umbra, penumbra, and the middle layer) separated distinctly at their perimeters. A layered penumbra is drawn as a series of simple orthogonal projections of an object locally magnified/shrunken