| dc.description.abstract | An efficient algorithm, HALO, is given to compute haloed line drawings of wire frame objects. Haloed line drawings are described by Appel et al.1HALO has two parts: CUT and DRAW. CUT uses an adaptive grid to find all edge intersections. It overlays a square grid, whose fineness is a function of the number and length of the edges, on the Scene. It determines the cells that each edge passes through, sorts these by cell to obtain the edges in each cell, and then, in each cell, tests each pair of edges in that cell for intersection. For broad classes of input this takes time linear in the number of edges plus the number of intersections. CUT writes a file containing all the locations where each edge is crossed in front by another. Given a halo width, DRAW reads this file edge by edge. For each edge, it subtracts and adds the halo width to each intersection to get the locations where the edge becomes invisible and visible. It sorts these along the edge, and then traverses the edge, plotting those portions where the number of"Visible" transitions is equal to the number of"invisible" transitions. DRAW takes time hear in the number of edge segments. Dividing HALO into two parts means that redrawing a plot with a different halo width is fast, since only DRAW need to be rerun.CR Categories and Subject Descriptions: I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling - geometric algorithm, languages, and systems- F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumerid Algorithms and Problems -geometrical problem and computationsGeneral Terms: Algorithms, design. | en_US |
