/**
* Set the partition bit to true for segments on the border and where the direction is 0
*
* @param sl
*/
private void setPartitionBitForCertainSegments(ArrayList<Seg> sl) {
for (int i = 0; i != sl.size(); i++) {
Seg se = sl.get(i);
if (((se.x == 0 || se.x == width) && se.dx == 0)
|| ((se.y == 0 || se.y == height) && se.dy == 0)) se.partition = true;
}
}
/**
* It generates the nodes. In every node, it has two section, left and right. It chooses the
* segment which has the minimum grade value and then split this node into two nodes through this
* segment. If all the segments in one node are partitioned, it will stop to split.
*
* @param sl
* @return root node for BSP tree
*/
private BSPNode genNodes(ArrayList<Seg> sl) {
// if there is no segment with a partition bit set to false, there is nothing else to do and we
// are at a leaf node
if (countNonPartitions(sl) == 0) return new BSPLeaf(sl);
// from the ones that have a partition bit set to false, pick a candidate with a low grade
Seg pe = findPartitionCandidate(sl);
// work on segment pe
// mark pe as partitioned
pe.partition = true;
final int x = pe.x;
final int y = pe.y;
final int dx = pe.dx;
final int dy = pe.dy;
final ArrayList<Seg> lsl = new ArrayList<Seg>();
final ArrayList<Seg> rsl = new ArrayList<Seg>();
for (int i = 0; i != sl.size(); i++) {
Seg se = (Seg) sl.get(i);
int df1x = se.x - x;
int df1y = se.y - y;
int sendx = se.x + se.dx;
int sendy = se.y + se.dy;
int df2x = sendx - x;
int df2y = sendy - y;
int nx = dy;
int ny = -dx;
int dot1 = df1x * nx + df1y * ny;
int dot2 = df2x * nx + df2y * ny;
if (getSign(dot1) != getSign(dot2)) {
if (dot1 == 0) dot1 = dot2;
else if (dot2 != 0) {
// we need to split this
int spx = se.x;
int spy = se.y;
if (dx == 0) spx = x;
else spy = y;
Seg sps1 = new Seg(se.x, se.y, spx - se.x, spy - se.y, se.dist, colchange);
Seg sps2 = new Seg(spx, spy, sendx - spx, sendy - spy, se.dist, colchange);
if (dot1 > 0) {
rsl.add(sps1);
lsl.add(sps2);
} else {
rsl.add(sps2);
lsl.add(sps1);
}
sps1.partition = sps2.partition = se.partition;
continue;
}
}
if (dot1 > 0 || (dot1 == 0 && se.getDir() == pe.getDir())) {
rsl.add(se);
if (dot1 == 0) se.partition = true;
} else if (dot1 < 0 || (dot1 == 0 && se.getDir() == -pe.getDir())) {
lsl.add(se);
if (dot1 == 0) se.partition = true;
} else {
dbg("error xx 1 " + dot1);
}
}
if (lsl.size() == 0) return new BSPLeaf(rsl);
if (rsl.size() == 0) return new BSPLeaf(lsl);
return new BSPBranch(x, y, dx, dy, genNodes(lsl), genNodes(rsl)); // recursion on both branches
}
