##### 点在多边形内的判别方法
``````int pnpoly(int nvert, float *vertx, float *verty, float testx, float testy)
{
int i, j, c = 0;
for (i = 0, j = nvert-1; i < nvert; j = i++)
{
if (((verty[i] > testy) != (verty[j] > testy)) &&
(testx < (vertx[j] - vertx[i]) * (testy - verty[i]) / (verty[j] - verty[i]) + vertx[i]) )
{
c = !c;
}
}
return c;
}
``````

Arguments

• nvert: Number of vertices in the polygon. Whether to repeat the first vertex at the end has been discussed in the article referred above.
• vertx, verty: Arrays containing the x- and y-coordinates of the polygon’s vertices.
• testx, testy: X- and y-coordinate of the test point.

https://stackoverflow.com/a/2922778/1645289

##### 点在两点之间的直线上的判别方法
``````bool isLieOnLine()
{
dxc = currPoint.x - point1.x;
dyc = currPoint.y - point1.y;

dxl = point2.x - point1.x;
dyl = point2.y - point1.y;

//point lies on the line if and only if (dxc * dyl - dyc * dxl) is equal to zero.
bool isCrossLine = dxc * dyl - dyc * dxl == 0;

if(isCrossLine)
{
if (abs(dxl) >= abs(dyl))
return dxl > 0 ?
point1.x <= currPoint.x && currPoint.x <= point2.x :
point2.x <= currPoint.x && currPoint.x <= point1.x;
else
return dyl > 0 ?
point1.y <= currPoint.y && currPoint.y <= point2.y :
point2.y <= currPoint.y && currPoint.y <= point1.y;
}

return false;
}
``````

https://stackoverflow.com/a/11908158/1645289

##### 参考

How to check if a given point lies inside or outside a polygon?
http://www.geeksforgeeks.org/how-to-check-if-a-given-point-lies-inside-a-polygon/

How to check if a point is inside a rectangle?
http://math.stackexchange.com/questions/190111/how-to-check-if-a-point-is-inside-a-rectangle

How can I determine whether a 2D Point is within a Polygon?
http://stackoverflow.com/questions/217578/how-can-i-determine-whether-a-2d-point-is-within-a-polygon#

How to check if a point lies on a line between 2 other points
https://stackoverflow.com/questions/11907947/how-to-check-if-a-point-lies-on-a-line-between-2-other-points

Check if a point belongs on a line segment
https://www.lucidar.me/en/mathematics/check-if-a-point-belongs-on-a-line-segment/