arma::vec2 Quad::getEdgePoints(double y) const {
// create the horizontal intersection line
ParametricLine<> scanLine;
scanLine.setFromDirection({1, 0}, {0, y});
// create a line-segment for each side of the quad
std::vector<ParametricLine<>> lines = {ParametricLine<>(tl, tr, true),
ParametricLine<>(tr, br, true),
ParametricLine<>(bl, br, true),
ParametricLine<>(bl, tl, true)};
// loop through lines and intersect it with the horizontal scan line
std::vector<double> values;
for (auto& line : lines) {
try {
values.push_back(scanLine.intersect(line)[0]);
}
catch (std::domain_error&) {
// did not intersect, ignore
}
}
// only two should intersect if there is a solution
if (values.size() != 2) {
throw std::domain_error("Could not find the edges points");
}
// return the minX and maxX
return {std::min(values[0], values[1]), std::max(values[0], values[1])};
}
// Use the raycasting method: any plane (equivalent to a line in 2D, but a plane for programming reasons)
// throught the point will intersect an even number of times with edges of the polygon iff the point lies
// within the polygon
bool Polygon::pointContained(const arma::vec2& p) const{
ParametricLine<2> ray;
int intersectionCount = 0;
ray.setFromDirection(arma::vec2{1,0}, p, arma::vec2({0,std::numeric_limits<double>::infinity()}));
arma::vec2 lastIntersection = {0,0};
bool hadPreviousIntersection = false;
for(auto& edge : edges){
try {
arma::vec2 intersection = ray.intersect(edge);
if(hadPreviousIntersection){
if(arma::norm(intersection - lastIntersection) > 1e-6){
intersectionCount++;
}
} else {
intersectionCount++;
}
hadPreviousIntersection = true;
lastIntersection = intersection;
} catch (const std::domain_error& e){
//We didnt intersect with the line!
//I know, seems kind of silly to use an exception here, but it works nicely with everything else
}
}
return (intersectionCount % 2) == 1;
}