Java Games Continued: Fun with Polygons - Pro Android Games - page 89

// Walk the edges of the polygon
for (int i = 0; i < npoints; lastx = curx, lasty = cury, i++) {
curx = xpoints[i];
cury = ypoints[i];
if (cury == lasty) {
continue;
}
int leftx;
if (curx < lastx) {
if (x >= lastx) {
continue;
}
leftx = curx;
} else {
if (x >= curx) {
continue;
}
leftx = lastx;
}
double test1, test2;
if (cury < lasty) {
if (y < cury || y >= lasty) {
continue;
}
if (x < leftx) {
hits++;
continue;
}
test1 = x - curx;
test2 = y - cury;
} else {
if (y < lasty || y >= cury) {
continue;
}
if (x < leftx) {
hits++;
continue;
}
test1 = x - lastx;
test2 = y - lasty;
}
if (test1 < (test2 / (lasty - cury) * (lastx - curx))) {
hits++;
}
}