判断点是否在三角形内

1 #include <iostream>
2 #include <algorithm>
3 #include <cmath>
4 using namespace std;
5
6 struct point {
7     double x, y;
8 };
9
10 struct v {
11     point start, end;
12 };
13
14
15 double dotProduct(v v1, v  v2) {
16     return (v1.end.x - v1.start.x)*(v2.end.x - v2.start.x) + (v1.end.y - v1.start.y)*(v2.end.y - v2.start.y);
17 }
18 double crossProduct(v v1, v v2) {
19     return (v1.end.x - v1.start.x)*(v2.end.y - v2.start.y) - (v2.end.x - v2.start.y)*(v1.end.y - v1.start.y);
20 }
21
22 bool inTriangle(point a,point b,point c, point p) {
23     v ab, ac, bc;
24     ab.start = a, ab.end = b;
25     ac.start = a, ac.end = c;
26     bc.start = b, bc.end = c;
27     double Sabc = fabs(crossProduct(ab, ac));
28
29     v pb;
30     pb.start = p, pb.end= b;
31     double Sabp = fabs(crossProduct(ab, pb));
32
33     v pc;
34     pc.start = p, pc.end = c;
35     double Sacp = fabs(crossProduct(ac, pc));
36
37     double Sbcp = fabs(crossProduct(bc, pc));
38
39     if (fabs(Sabc - Sabp - Sacp - Sbcp) < 1e-5)
40         return true;
41     return false;
42 }
43
44
45 int main() {
46     point p1, p2, p3,p0;
47     while (cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y >> p0.x >> p0.y) {
48         cout << inTriangle(p1, p2, p3, p0);
49     }
50 }