Real-Time Stroke Textures
Author(s): Bert Freudenberg.
Misc: Technical Sketch presented at SIGGRAPH 2001,
2001.
[BibTeX] 
Abstract:
Shading in line drawings is expressed by varying the
stroke width or density of strokes covering an object's
surface. In their pioneering work, Winkenbach and
Salesin introduced the concept of "prioritized stroke
textures" to the emerging field of non-photorealistic
rendering1. Despite the advances in processing power
in the years since then, the sheer number of lines to
draw prevents this method from running in real-time. A
real-time approach for hatching was presented by Lake
et al.2, which chooses from a set of textures based on
the brightness at vertices, subdividing polygons if
necessary. However, the method is very CPU-heavy
and requires many polygons.