Region with pre-allocated buffer.

This class provides the functionality of an RRegion, but in addition, for optimisation purposes, uses a buffer containing pre-allocated space for as many rectangles as are specified in the granularity.

When this buffer is full, cell allocation takes place as for an RRegion, and the RRegionBuf effectively becomes an RRegion. In this case, the region does not revert to using the buffer, even if the region were to shrink so that the buffer could, once again, contain the region. When the region is no longer required, call Close(), defined in the base class RRegion, to free up all memory.