# [fpc-pascal] C translation question

Ryan Joseph ryan at thealchemistguild.com
Sat Oct 22 11:06:04 CEST 2016

```I’m trying to translate a function from C (taken from http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html) and although I think I got it correctly it’s not behaving 100% accurately so I’m not sure if it was my translation or not. The “for” statement is pretty confusing to my eyes despite the author of the function giving a description of his code.

Does anyone spot any errors with my translation?

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;
}

function TPolygonHelper.ContainsPoint (point: TPoint): boolean;
var
i, j, c: integer;
begin
i := 0;
j := high(self);
c := 0;
for i := 0 to high(self) do
begin
j := i + 1;
if ((self[i].y > point.y) <> (self[j].y > point.y))
and (point.x < (self[j].x - self[i].x) * (point.y - self[i].y) / (self[j].y - self[i].y) + self[i].x) then
c := not c;
end;
result := c <> 0;
end;

Regards,
Ryan Joseph

```