判断点与三角形的关系

#include <stdio.h>
#include <math.h>

struct _point {
    double x;
    double y;
};
typedef struct _point point;

struct _triangle {
    point a;
    point b;
    point c;
};
typedef struct _triangle triangle;

int check(triangle t, point p);

int
main(void)
{
    triangle t;
    t.a.x = 1;
    t.a.y = 1;
    t.b.x = 3;
    t.b.y = 1;
    t.c.x = 3;
    t.c.y = 2;

    point p;
    p.x = 2;
    p.y = 2;

    point q;
    q.x = 3;
    q.y = 3;

    point r;
    r.x = 2;
    r.y = 1;

    printf("Res: %d\n", check(t, p));
    printf("Res: %d\n", check(t, q));
    printf("Res: %d\n", check(t, r));

    return 0;
}

double
distance(point p1, point p2)
{
    double res;
    double x = p1.x - p2.x;
    double y = p1.y - p2.y;
    res = sqrt(x*x + y*y);

    return res;
}

double
area(point p1, point p2, point p3)
{
    double res;
    double a = distance(p1, p2);
    double b = distance(p2, p3);
    double c = distance(p3, p1);
    double p = (a + b + c) / 2;
    res = sqrt(p*(p-a)*(p-b)*(p-c));

    return res;
}

int
check(triangle t, point p)
{
    double res;
    double base = area(t.a, t.b, t.c);
    double x = area(t.a, t.b, p);
    double y = area(t.b, t.c, p);
    double z = area(t.c, t.a, p);

    if (base <= (x+y+z))
        if (0 != x && 0 != y && 0 != z)
            return 1;
        else
            return 0;
    else
        return (-1);
}

• 1: 内
• 0: 边
• -1：外