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When talking about stroking, we mean tracing a pen of finite width along
these subpaths. When doing so, a new finite (more complex) region of ink is
built. Actually we can consider this filled region being the result of filling
a newly created path that consists of two subpaths surrounding the original
path and having appropriate directions. These newly created subpaths are
referred as the right path and the left path.
Figure illustrates this idea for the
character ``o''. The original path is represented by dashed curves whereas
left paths and right paths are shown as solid curves. The respective
directions are indicated by arrows.
Now, what are the steps required to compute a right path or left path from a
given path and given a certain strokewidth? Firstly, for each path segment two
parallel paths the right and the left path, located half the strokewidth
right and left of the original path have to be computed. This is shown for the
character ``t'' in Figure , .
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In particular, it turns out that in order to connect two parallel right or left paths of two neighboring original path segments, additional path segments are required. Therefore, in a second step, these parallel path segments--which in general may be disjoint--have to be connected appropriately. These additional path segments are shown in of the figure. We term these path segments Prolongation Segments. They are always built as straight lines. It is also obvious, that for convex edges, prolongation actually is what it indicates, and for concave edges, some trick must be applied so that prolongation yields a path that actually shortens the respective parallel path segments.