Cross-hatched shadow line maps

Cross-hatching is an artistic drawing method in which lines of variable thickness and orientation approximate tonal variations associated with shading and shadowing. Research in computer graphics has focused primarily on creating illustrations with cross-hatching that conforms to the three dimensional surface of virtual objects. Cross-hatched shadow maps apply cross-hatching to shadowed areas, with the length of these hatching lines based on the distance shadows are cast from point illumination sources at a number of discrete inclinations above the horizon. Thickness of lines increase within areas remaining shadowed at greater inclinations. By adding hatching lines from a second illumination azimuth, the resulting map is both cross-hatched and rendered with more diffuse shadows. The resulting map uses only shadows to represent terrain, a departure from other techniques such as hill-shading.