/**
* Find the intersection point between a line segment and the current
* partition plane. Takes advantage of some common situations like
* horizontal and vertical lines to choose a 'nicer' intersection point.
*/
Vector2d intersectPartition(LineSegmentSide const &seg, coord_t fromDist,
coord_t toDist) const
{
// Horizontal partition vs vertical line segment.
if(hplane.slopeType() == ST_HORIZONTAL && seg.slopeType() == ST_VERTICAL)
{
return Vector2d(seg.from().origin().x, hplane.partition().origin.y);
}
// Vertical partition vs horizontal line segment.
if(hplane.slopeType() == ST_VERTICAL && seg.slopeType() == ST_HORIZONTAL)
{
return Vector2d(hplane.partition().origin.x, seg.from().origin().y);
}
// 0 = start, 1 = end.
coord_t ds = fromDist / (fromDist - toDist);
Vector2d point = seg.from().origin();
if(seg.slopeType() != ST_VERTICAL)
point.x += seg.direction().x * ds;
if(seg.slopeType() != ST_HORIZONTAL)
point.y += seg.direction().y * ds;
return point;
}
/**
* Take the given line segment @a lineSeg, compare it with the partition
* plane and determine into which of the two sets it should be. If the
* line segment is found to intersect the partition, the intercept point
* is determined and the line segment then split in two at this point.
* Each piece of the line segment is then added to the relevant set.
*
* If the line segment is collinear with, or intersects the partition then
* a new intercept is added to the partitioning half-plane.
*
* @note Any existing @em twin of @a lineSeg is so too handled uniformly.
*
* @param seg Line segment to be "partitioned".
* @param rights Set of line segments on the right side of the partition.
* @param lefts Set of line segments on the left side of the partition.
*/
void divideOneSegment(LineSegmentSide &seg, LineSegmentBlockTreeNode &rights,
LineSegmentBlockTreeNode &lefts)
{
coord_t fromDist, toDist;
LineRelationship rel = hplane.relationship(seg, &fromDist, &toDist);
switch(rel)
{
case Collinear: {
interceptPartition(seg, LineSegment::From);
interceptPartition(seg, LineSegment::To);
// Direction (vs that of the partition plane) determines in which
// subset this line segment belongs.
if(seg.direction().dot(hplane.partition().direction) < 0)
{
linkLineSegmentInBlockTree(lefts, seg);
}
else
{
linkLineSegmentInBlockTree(rights, seg);
}
break; }
case Right:
case RightIntercept:
if(rel == RightIntercept)
{
// Direction determines which edge of the line segment interfaces
// with the new half-plane intercept.
interceptPartition(seg, (fromDist < DIST_EPSILON? LineSegment::From : LineSegment::To));
}
linkLineSegmentInBlockTree(rights, seg);
break;
case Left:
case LeftIntercept:
if(rel == LeftIntercept)
{
interceptPartition(seg, (fromDist > -DIST_EPSILON? LineSegment::From : LineSegment::To));
}
linkLineSegmentInBlockTree(lefts, seg);
break;
case Intersects: {
// Calculate the intersection point and split this line segment.
Vector2d point = intersectPartition(seg, fromDist, toDist);
LineSegmentSide &newFrontRight = splitLineSegment(seg, point);
// Ensure the new back left segment is inserted into the same block as
// the old back right segment.
if(LineSegmentBlockTreeNode *backLeftBlock = (LineSegmentBlockTreeNode *)seg.back().blockTreeNodePtr())
{
linkLineSegmentInBlockTree(*backLeftBlock, newFrontRight.back());
}
interceptPartition(seg, LineSegment::To);
// Direction determines which subset the line segments are added to.
if(fromDist < 0)
{
linkLineSegmentInBlockTree(rights, newFrontRight);
linkLineSegmentInBlockTree(lefts, seg);
}
else
{
linkLineSegmentInBlockTree(rights, seg);
linkLineSegmentInBlockTree(lefts, newFrontRight);
}
break; }
}
}