Real-time ray-casting and advanced shading of discrete isosurfaces

This paper presents a real-time rendering pipeline for implicit surfaces defined by a regular volumetric grid of samples. We use a ray-casting approach on current graphics hardware to perform a direct rendering of the isosurface. A two-level hierarchical representation of the regular grid is employed to allow object-order and image-order empty space skipping and circumvent memory limitations of graphics hardware. Adaptive sampling and iterative refinement lead to high-quality ray/surface intersections. All shading operations are deferred to image space, making their computational effort independent of the size of the input data. A continuous third-order reconstruction filter allows on-the-fly evaluation of smooth normals and extrinsic curvatures at any point on the surface without interpolating data computed at grid points. With these local shape descriptors, it is possible to perform advanced shading using high-quality lighting and non-photorealistic effects in real-time.