// Globals which should be set before calling these functions:
//
// int polyCorners = how many corners the polygon has (no repeats)
// float polyX[] = horizontal coordinates of corners
// float polyY[] = vertical coordinates of corners
// float x, y = point to be tested
//
// The following global arrays should be allocated before calling these functions:
//
// float constant[] = storage for precalculated constants (same size as polyX)
// float multiple[] = storage for precalculated multipliers (same size as polyX)
//
// (Globals are used in this example for purposes of speed. Change as
// desired.)
//
// USAGE:
// Call precalc_values() to initialize the constant[] and multiple[] arrays,
// then call pointInPolygon(x, y) to determine if the point is in the polygon.
//
// The function will return YES if the point x,y is inside the polygon, or
// NO if it is not. If the point is exactly on the edge of the polygon,
// then the function may return YES or NO.
//
// Note that division by zero is avoided because the division is protected
// by the "if" clause which surrounds it.

void precalc_values() {

int i, j=polyCorners-1 ;

for(i=0; i<polyCorners; i++) {
if(polyY[j]==polyY[i]) {
constant[i]=polyX[i];
multiple[i]=0; }
else {
constant[i]=polyX[i]-(polyY[i]*polyX[j])/(polyY[j]-polyY[i])+(polyY[i]*polyX[i])/(polyY[j]-polyY[i]);
multiple[i]=(polyX[j]-polyX[i])/(polyY[j]-polyY[i]); }
j=i; }}

bool pointInPolygon() {

int i, j=polyCorners-1 ;
bool oddNodes=NO ;

for (i=0; i<polyCorners; i++) {
if ((polyY[i]< y && polyY[j]>=y
|| polyY[j]< y && polyY[i]>=y)) {
oddNodes^=(y*multiple[i]+constant[i]<x); }
j=i; }

return oddNodes; }

Quote:

// Note that division by zero is avoided because the division is protected
// by the "if" clause which surrounds it.

 //check the intersections
if (((polyK.Y > currentPoint.Y) != (polyJ.Y > currentPoint.Y)) &&
     (currentPoint.X < (polyJ.X - polyK.X) * (currentPoint.Y - polyK.Y) / (polyJ.Y - polyK.Y) + polyK.X)) 
    

What of it when the God Of C and Assembly seeketh help from mortals?

I need help creating a very fast 'FASM' variant of [snip] (Help greatly appreciated)

Just trust me, it's not for evil, it's for good. Prove your worth, it's good sport too.