Abstracted away the angle comparison

Author: Chillee

content/geometry/HalfPlane.h

@@ -19,18 +19,20 @@ typedef Point<double> P;
 typedef array<P, 2> Line;
 #define sp(a) a[0], a[1]
 #define ang(a) atan2((a[1] - a[0]).y, (a[1] - a[0]).x)
+
+int angDiff(Line a, Line b) { return sgn(ang(a) - ang(b)); }
 bool cmp(Line a, Line b) {
-	auto s = ang(a) - ang(b);
+	auto s = angDiff(a, b);
 	return s == 0 ? sideOf(sp(b), a[0]) >= 0 : s < 0;
 }
 vector<P> halfPlaneIntersection(vector<Line> vs) {
 	sort(all(vs), cmp);
 	vector<Line> deq(sz(vs) + 5);
 	vector<P> ans(sz(vs) + 5);
-	int dh = 0, dt = 1, ah = 0, at = 0;
 	deq[0] = vs[0];
+	int dh = 0, dt = 1, ah = 0, at = 0;
 	for (int i = 1; i < sz(vs); ++i) {
-		if (ang(vs[i]) - ang(vs[i - 1]) == 0) continue;
+		if (angDiff(vs[i], vs[i - 1]) == 0) continue;
 		while (ah<at && sideOf(sp(vs[i]),ans[at-1]) < 0) at--,dt--;
 		while (ah<at && sideOf(sp(vs[i]),ans[ah]) < 0) ah++,dh++;
 		ans[at++] = lineInter(sp(deq[dt - 1]), sp(vs[i])).second;

fuzz-tests/geometry/HalfPlane.cpp

@@ -12,7 +12,6 @@ typedef vector<int> vi;
 
 #include "../../content/geometry/HalfPlane.h"
 #include "../../content/geometry/PolygonArea.h"
-typedef Point<double> P;
 
 ostream &operator<<(ostream &os, P p) { return cout << "(" << p.x << "," << p.y << ")"; }
 
@@ -203,8 +202,8 @@ void testEmpty() {
     assert(sz(res) == 0);
 }
 void testRandom() {
-    int lim = 1e2;
-    for (int i = 0; i < 1000; i++) {
+    int lim = 1e1;
+    for (int i = 0; i < 10000; i++) {
         vector<Line> t;
         for (int i = 0; i < 6; i++) {
             Line cand{P(0, 0), P(0, 0)};
@@ -228,8 +227,8 @@ void testRandom() {
         assert(diff < EPS);
     }
 }
-void testConvex() {
-
+void testSelf() {
+    int lim = 1e2;
 }
 
 int main() {
@@ -239,6 +238,13 @@ int main() {
     testPoint();
     testEmpty();
     testRandom();
+    vector<Line> t({{P(0,0), P(5,0)}, {P(0,1), P(5,1)}});
+    reverse(all(t));
+    addInf(t);
+
+    auto res = halfPlaneIntersection(t);
+    for (auto i: res) cout<<i<<' ';
+    cout<<endl;
     // Failure case for MIT's half plane code
     // vector<Line> t({{P(9, 8), P(9, 1)}, {P(3, 3), P(3, 5)}, {P(7, 6), P(0, 8)}});
     // addInf(t);