We present and evaluate a new approach for real-time rendering of composable 3D lenses for polygonal scenes. Such lenses, usually called "volumetric lenses," are an extension of 2D Magic Lenses to 3D volumes in which effects are applied to scene elements. Although the composition of 2D lenses is well known, 3D composition was long considered infeasible due to both geometric and semantic complexity. Nonetheless, for a scene with multiple interactive 3D lenses, the problem of intersecting lenses must be considered. Intersecting 3D lenses in meaningful ways supports new interfaces such as hierarchical 3D windows, 3D lenses for managing and composing visualization options, or interactive shader development by direct manipulation of lenses providing component effects. Our 3D volumetric lens approach differs from other approaches and is one of the first to address efficient composition of multiple lenses. It is well-suited to head-tracked VR environments because it requires no view-dependent generation of major data structures, allowing caching and reuse of full or partial results. A Composite Shader Factory module composes shader programs for rendering composite visual styles and geometry of intersection regions. Geometry is handled by Boolean combinations of region tests in fragment shaders, which allows both convex and nonconvex CSG volumes for lens shape. Efficiency is further addressed by a Region Analyzer module and by broad-phase culling. Finally, we consider the handling of order effects for composed 3D lenses.

We demonstrate composable volumetric lenses as interpretational tools for geological visualization. The lenses provide a constrained focus region that provides alternative views of datasets to the user while maintaining the context of surrounding features. Our rendering method is based on run-time composition of GPU shader programs that implement per-fragment clipping to lens boundaries and surface shader evaluation. It supports composition of lenses and the user can influence the resulting visualization by interactively changing the order in which the individual lens effects are applied. Multiple shader effects have been created and used for interpretation of high-resolution elevation datasets (like LTDAR and SRTM) in our lab.

Various virtual and augmented reality systems include volumetric lenses, an extension of 2D magic lenses to 3D volumes in which effects are applied to scene elements. We present a new 3D volumetric lens rendering system that differs fundamentally from other approaches and that is the first to address efficient real-time composition of multiple 3D lenses. A lens factory module composes chainable shader programs for rendering composite visual styles and geometry of intersection regions. Geometry is handled by Boolean combinations of region tests in fragment shaders, which allows both convex and non-convex CSG volumes for lens shape. Efficiency is further addressed by a region analyzer module and by broad-phase culling. Finally, we consider the handling of order effects for composed 3D lenses.