三角形几何判断模板

原博客地址http://blog.csdn.net/jnxxhzz/article/details/75738521

1.两线段是否相交  2.点是否在三角形内




1.两线段是否相交

double mult(Point a, Point b, Point c)    
{    
    return (a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y);    
}    
    
//aa, bb为一条线段两端点 cc, dd为另一条线段的两端点 相交返回true, 不相交返回false    
bool intersect(Point aa, Point bb, Point cc, Point dd)    
{    
    if ( max(aa.x, bb.x)<min(cc.x, dd.x) )    
    {    
        return false;    
    }    
    if ( max(aa.y, bb.y)<min(cc.y, dd.y) )    
    {    
        return false;    
    }    
    if ( max(cc.x, dd.x)<min(aa.x, bb.x) )    
    {    
        return false;    
    }    
    if ( max(cc.y, dd.y)<min(aa.y, bb.y) )    
    {    
        return false;    
    }    
    if ( mult(cc, bb, aa)*mult(bb, dd, aa)<0 )    
    {    
        return false;    
    }    
    if ( mult(aa, dd, cc)*mult(dd, bb, cc)<0 )    
    {    
        return false;    
    }    
    return true;    
}    

2.点是否在三角形内

/**  
* @brief 计算三角形面积  
*/    
float GetTriangleSquar(const Point pt0, const Point pt1, const Point pt2)    
{    
    Point AB,   BC;        
    AB.x = pt1.x - pt0.x;       
    AB.y = pt1.y - pt0.y;       
    BC.x = pt2.x - pt1.x;       
    BC.y = pt2.y - pt1.y;         
    return fabs((AB.x * BC.y - AB.y * BC.x)) / 2.0f;        
}    
    
/**  
* @brief 判断给定一点是否在三角形内或边上  
*/    
bool IsInTriangle(const Point A, const Point B, const Point C, const Point D)    
{    
    float SABC, SADB, SBDC, SADC;    
    SABC = GetTriangleSquar(A, B, C);    
    SADB = GetTriangleSquar(A, D, B);    
    SBDC = GetTriangleSquar(B, D, C);    
    SADC = GetTriangleSquar(A, D, C);    
  <span style="white-space:pre">    </span>//if (!SADB||!SBDC||!SADC) return false;  在三角形边上返回false   
    float SumSuqar = SADB + SBDC + SADC;    
    
    if ((-ABS_FLOAT_0 < (SABC - SumSuqar)) && ((SABC - SumSuqar) < ABS_FLOAT_0))    
    {    
        return true;    
    }    
    else    
    {    
        return false;    
    }    
}