void R2::OpenSegment(unsigned Identity)
This function opens a segment.
The identity of the segment to be opened.
By default, a newly created segment is chained. The method SetSegmentAttributes may be used to set a segment to unchained.
Chained segments are drawn in ascending order of segment identity. That is, the higher the segment identity, the uppermost in the z-order the segment is drawn.
If the segment exists, it is opened with its element pointer set to zero. This means that the segment is ready for editing.