In porting ZooLib to BeOS I found that BeOS's region API was missing key features. Exclusive or and equivalence testing could be handled by composing more primitive operations, but insetting was trickier. So I dug through the X source and found that their implementation of insetting was totally generic, basically shifting the source region for each set bit in the inset distance and accumulating a union (for expanding) or intersection (for contracting).

But BRegion was also quite slow. The internal representation was pretty close to that used by the X code, being a list of non-overlapping rectangles organized into bands. BRegion did not always maintain the same tight constraints as the X code, but it still proved possible to significantly improve performance by manipulating BRegion's internal data using the X code.

By this point I was intimately familiar with X regions and it was a small step to take the X source and rework it, the result being ZBigRegion - a portable region implementation using 32 bit coordinates. Combined with ZDCPixmapBlit it forms the basis of ZDC_ZooLib.