Real - time rendering of normal maps with discontinuities

Normal mapping uses normal perturbations stored in a texture to give objects a more geometrically complex appearance without increasing the number of geometric primitives. Standard biand trilinear interpolation of normal maps works well if the normal field is continuous, but may result in visible artifacts in the areas where the field is discontinuous, which is common for surfaces with creases and dents. In this paper we describe a real-time rendering technique which preserves the discontinuity curves of the normal field at sub-pixel level and its GPU implementation. Our representation of the piecewise-continuous normal field is based on approximations of the distance function to the discontinuity set and its gradient. Using these approximations we can efficiently reconstruct discontinuities at arbitrary resolution and ensure that no normals are interpolated across the discontinuity. We also described a method for updating the normal field along the discontinuities in real-time based on blending the original field with the one calculated from a user-defined surface profile.