/**
* compute the convex hull of a collection of Points
*
* @param points the points as a Vector2 array.
* @param pointsLength the number of vertices of the polygon.
* @param retPoly pre allocated array of floats to put the vertices
* @return the number of points in the polygon 0 if no intersection
*/
int SpotShadow::hull(Vector2* points, int pointsLength, Vector2* retPoly) {
xsort(points, pointsLength);
int n = pointsLength;
Vector2 lUpper[n];
lUpper[0] = points[0];
lUpper[1] = points[1];
int lUpperSize = 2;
for (int i = 2; i < n; i++) {
lUpper[lUpperSize] = points[i];
lUpperSize++;
while (lUpperSize > 2 && !ccw(
lUpper[lUpperSize - 3].x, lUpper[lUpperSize - 3].y,
lUpper[lUpperSize - 2].x, lUpper[lUpperSize - 2].y,
lUpper[lUpperSize - 1].x, lUpper[lUpperSize - 1].y)) {
// Remove the middle point of the three last
lUpper[lUpperSize - 2].x = lUpper[lUpperSize - 1].x;
lUpper[lUpperSize - 2].y = lUpper[lUpperSize - 1].y;
lUpperSize--;
}
}
Vector2 lLower[n];
lLower[0] = points[n - 1];
lLower[1] = points[n - 2];
int lLowerSize = 2;
for (int i = n - 3; i >= 0; i--) {
lLower[lLowerSize] = points[i];
lLowerSize++;
while (lLowerSize > 2 && !ccw(
lLower[lLowerSize - 3].x, lLower[lLowerSize - 3].y,
lLower[lLowerSize - 2].x, lLower[lLowerSize - 2].y,
lLower[lLowerSize - 1].x, lLower[lLowerSize - 1].y)) {
// Remove the middle point of the three last
lLower[lLowerSize - 2] = lLower[lLowerSize - 1];
lLowerSize--;
}
}
// output points in CW ordering
const int total = lUpperSize + lLowerSize - 2;
int outIndex = total - 1;
for (int i = 0; i < lUpperSize; i++) {
retPoly[outIndex] = lUpper[i];
outIndex--;
}
for (int i = 1; i < lLowerSize - 1; i++) {
retPoly[outIndex] = lLower[i];
outIndex--;
}
// TODO: Add test harness which verify that all the points are inside the hull.
return total;
}
static void
vsort_xsort(struct vsort_timing *vt, size_t loops)
{
size_t n = loops;
while (n-- > 0) {
memcpy(vt->copy, vt->data, vt->len);
xsort(vt->copy, vt->items, vt->isize, vsort_long_cmp);
}
}
