private static boolean constructPolygonForIntersection(
ArrayList<Boolean> decrementP,
int[][][] crossingIndices,
ConvexPolygon2d polygonP,
ConvexPolygon2d polygonQ,
ConvexPolygon2d intersectingPolygonToPack) {
int startIndexP1 = crossingIndices[0][0][0];
int endIndexP1 = crossingIndices[0][0][1];
int startIndexQ1 = crossingIndices[0][1][0];
int endIndexQ1 = crossingIndices[0][1][1];
// Want to do things in clockwise order so that making the new polygon is fast. Should only be
// one of two cases.
// a) P1/Q2 start->end increments, P2/Q1 start->end decrement; OR
// b) P2/Q1 start->end increments, P1/Q2 start->end decrement; OR
boolean incrementPNext;
if ((startIndexP1 + 1) % polygonP.getNumberOfVertices() == endIndexP1) {
incrementPNext = true;
} else if ((startIndexQ1 + 1) % polygonQ.getNumberOfVertices() == endIndexQ1) {
incrementPNext = false;
} else {
throw new RuntimeException("Neither P1, nor P2 increment!!!");
}
intersectingPolygonToPack.clear();
// Start at the first intersection. Add it. Then march to the next intersection. Then continue.
for (int i = 0; i < crossingIndices.length; i++) {
int startIndexP = crossingIndices[i][0][0];
int endIndexP = crossingIndices[i][0][1];
int startIndexQ = crossingIndices[i][1][0];
int endIndexQ = crossingIndices[i][1][1];
Point2d startP = polygonP.getVertex(startIndexP);
Point2d endP = polygonP.getVertex(endIndexP);
Point2d startQ = polygonQ.getVertex(startIndexQ);
Point2d endQ = polygonQ.getVertex(endIndexQ);
Point2d intersection =
GeometryTools.getIntersectionBetweenTwoLines(startP, endP, startQ, endQ);
intersectingPolygonToPack.addVertex(intersection);
if (incrementPNext) {
int indexP = crossingIndices[i][0][1]; // endIndexP;
int indexPNext = crossingIndices[(i + 1) % crossingIndices.length][0][0];
// System.out.println("indexP = " + indexP + ", indexPNext = " + indexPNext);
while (indexP != indexPNext) {
intersectingPolygonToPack.addVertex(polygonP.getVertex(indexP));
indexP = polygonP.getNextVertexIndex(indexP);
}
} else {
int indexQ = crossingIndices[i][1][1]; // endIndexQ;
int indexQNext = crossingIndices[(i + 1) % crossingIndices.length][1][0];
// System.out.println("indexQ = " + indexQ + ", indexQNext = " + indexQNext);
while (indexQ != indexQNext) {
intersectingPolygonToPack.addVertex(polygonQ.getVertex(indexQ));
indexQ = polygonQ.getNextVertexIndex(indexQ);
}
}
incrementPNext = !incrementPNext;
}
intersectingPolygonToPack.update();
if (intersectingPolygonToPack.isEmpty()) return false;
return true;
}
