原博客地址http://blog.csdn.net/jnxxhzz/article/details/75738521
1.兩線段是否相交 2.點是否在三角形內
1.兩線段是否相交
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爲一條線段兩端點 cc, dd爲另一條線段的兩端點 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.點是否在三角形內/**
* @brief 計算三角形面積
*/
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 判斷給定一點是否在三角形內或邊上
*/
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; 在三角形邊上返回false
float SumSuqar = SADB + SBDC + SADC;
if ((-ABS_FLOAT_0 < (SABC - SumSuqar)) && ((SABC - SumSuqar) < ABS_FLOAT_0))
{
return true;
}
else
{
return false;
}
}