The.Algorithm.Design.Manual.Springer-Verlag.1998

War Story: Stripping Triangulations
Figure: A bounded height priority queue for triangle strips
● Priority Queue - Since we were repeatedly interested in identifying the longest possible next strip,
we needed a priority queue to store the strips, ordered according to length. The next strip to peel
would always be the top of the queue. Our priority queue had to permit reducing the priority of
arbitrary elements of the queue whenever we updated the strip lengths to reflect what triangles
were peeled away. Because all of the strip lengths were bounded by a fairly small integer
(hardware constraints prevent any strip from having more than 256 vertices), we used a bounded
height priority queue (shown in Figure and described in Section ). An ordinary heap would
also have worked just fine.
To update a queue entry associated with a triangle, we needed to be able to quickly find where it
was. This meant that we also needed a ...
● Dictionary - For each triangle in the mesh, we needed a way to find where it was in the queue.
This meant storing a pointer for each triangle. Since each triangle was defined by three integer
vertex numbers, either a hash table or an array of lists of triangles would suffice. By integrating
this dictionary with the priority queue, we built a data structure capable of a wider range of
operations.
Although there were various other complications, such as quickly recalculating the length of the strips
affected by the peeling, the key idea needed to obtain better performance was to use the priority queue.
Run time improved by several orders of magnitude after employing these data structures.
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