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Only reinspect segments that changed in the previous pass
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@e-n-f
e-n-f committed Nov 13, 2023
1 parent d23f0a2 commit 1238711
Showing 1 changed file with 59 additions and 24 deletions.
83 changes: 59 additions & 24 deletions polygon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ struct point {

typedef std::pair<point, point> segment;

bool fix_opposites(std::vector<segment> &segs) {
bool fix_opposites(std::vector<segment> &segs, std::set<segment> &affected) {
bool changed = false;
std::multimap<segment, size_t> opposites;
segment erased = std::make_pair(point(INT_MAX, INT_MAX), point(INT_MAX, INT_MAX));
Expand Down Expand Up @@ -73,6 +73,9 @@ bool fix_opposites(std::vector<segment> &segs) {

segs.emplace_back(point(cx, cy), segs[i].second);
segs[i] = std::make_pair(segs[i].first, point(cx, cy));

affected.insert(segs[i]);
affected.insert(segs.back());
changed = true;

// segs[i] is not erased, so segs[f.first->second]
Expand Down Expand Up @@ -107,6 +110,7 @@ const std::pair<double, double> SAME_SLOPE = std::make_pair(-INT_MAX, INT_MAX);
// which does not seem to produce correct results.
std::pair<double, double> get_line_intersection(long long p0_x, long long p0_y, long long p1_x, long long p1_y,
long long p2_x, long long p2_y, long long p3_x, long long p3_y) {
// bounding box reject, x
long long min01x = std::min(p0_x, p1_x);
long long max01x = std::max(p0_x, p1_x);
long long min23x = std::min(p2_x, p3_x);
Expand All @@ -115,6 +119,7 @@ std::pair<double, double> get_line_intersection(long long p0_x, long long p0_y,
return std::make_pair(-1, -1);
}

// bounding box reject, y
long long min01y = std::min(p0_y, p1_y);
long long max01y = std::max(p0_y, p1_y);
long long min23y = std::min(p2_y, p3_y);
Expand Down Expand Up @@ -142,32 +147,38 @@ std::pair<double, double> get_line_intersection(long long p0_x, long long p0_y,
return SAME_SLOPE;
}

bool vertical(std::vector<segment> &segs, size_t s, long long y) {
bool vertical(std::vector<segment> &segs, size_t s, long long y, std::set<segment> &affected) {
if ((y > segs[s].first.y && y < segs[s].second.y) ||
(y > segs[s].second.y && y < segs[s].first.y)) {
segs.push_back(std::make_pair(point(segs[s].first.x, y), segs[s].second));
segs[s] = std::make_pair(segs[s].first, point(segs[s].first.x, y));

affected.insert(segs[s]);
affected.insert(segs.back());
return true;
}

return false;
}

bool horizontal(std::vector<segment> &segs, size_t s, long long x) {
bool horizontal(std::vector<segment> &segs, size_t s, long long x, std::set<segment> &affected) {
if ((x > segs[s].first.x && x < segs[s].second.x) ||
(x > segs[s].second.x && x < segs[s].first.x)) {
double slope = (segs[s].second.y - segs[s].first.y) /
(double) (segs[s].second.x - segs[s].first.x);
long long y = std::llround(segs[s].first.y + slope * (x - segs[s].first.x));
segs.push_back(std::make_pair(point(x, y), segs[s].second));
segs[s] = std::make_pair(segs[s].first, point(x, y));

affected.insert(segs[s]);
affected.insert(segs.back());
return true;
}

return false;
}

bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2, std::set<segment> &affected) {
bool changed = false;

if (segs[s1].first.x == segs[s1].second.x) {
Expand All @@ -179,16 +190,16 @@ bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
if (segs[s1].first.x == segs[s2].first.x) {
// collinear, not parallel

if (vertical(segs, s1, segs[s2].first.y)) {
if (vertical(segs, s1, segs[s2].first.y, affected)) {
changed = true;
}
if (vertical(segs, s1, segs[s2].second.y)) {
if (vertical(segs, s1, segs[s2].second.y, affected)) {
changed = true;
}
if (vertical(segs, s2, segs[s1].first.y)) {
if (vertical(segs, s2, segs[s1].first.y, affected)) {
changed = true;
}
if (vertical(segs, s2, segs[s1].second.y)) {
if (vertical(segs, s2, segs[s1].second.y, affected)) {
changed = true;
}
}
Expand All @@ -215,16 +226,16 @@ bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
if (y1 == y2) {
// collinear, not parallel

if (horizontal(segs, s1, segs[s2].first.x)) {
if (horizontal(segs, s1, segs[s2].first.x, affected)) {
changed = true;
}
if (horizontal(segs, s1, segs[s2].second.x)) {
if (horizontal(segs, s1, segs[s2].second.x, affected)) {
changed = true;
}
if (horizontal(segs, s2, segs[s1].first.x)) {
if (horizontal(segs, s2, segs[s1].first.x, affected)) {
changed = true;
}
if (horizontal(segs, s2, segs[s1].second.x)) {
if (horizontal(segs, s2, segs[s1].second.x, affected)) {
changed = true;
}
}
Expand All @@ -240,7 +251,7 @@ bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
return changed;
}

bool intersect(std::vector<segment> &segs, size_t s1, size_t s2) {
bool intersect(std::vector<segment> &segs, size_t s1, size_t s2, std::set<segment> &affected) {
auto intersections = get_line_intersection(segs[s1].first.x, segs[s1].first.y,
segs[s1].second.x, segs[s1].second.y,
segs[s2].first.x, segs[s2].first.y,
Expand All @@ -258,7 +269,10 @@ bool intersect(std::vector<segment> &segs, size_t s1, size_t s2) {
// printf("introduce %f,%f in %f,%f to %f,%f (s1 %zu %zu)\n", x, y, segs[s1].first.x, segs[s1].first.y, segs[s1].second.x, segs[s1].second.y, s1, s2);
segs.push_back(std::make_pair(point(x, y), segs[s1].second));
segs[s1] = std::make_pair(segs[s1].first, point(x, y));

changed = true;
affected.insert(segs[s1]);
affected.insert(segs.back());
}

if ((x == segs[s2].first.x && y == segs[s2].first.y) ||
Expand All @@ -269,10 +283,13 @@ bool intersect(std::vector<segment> &segs, size_t s1, size_t s2) {
// printf("introduce %lld,%lld in %lld,%lld to %lld,%lld (s2)\n", std::llround(x), std::llround(y), std::llround(segs[s2].first.x), std::llround(segs[s2].first.y), std::llround(segs[s2].second.x), std::llround(segs[s2].second.y));
segs.push_back(std::make_pair(point(x, y), segs[s2].second));
segs[s2] = std::make_pair(segs[s2].first, point(x, y));

changed = true;
affected.insert(segs[s2]);
affected.insert(segs.back());
}
} else if (intersections == SAME_SLOPE) {
if (intersect_collinear(segs, s1, s2)) {
if (intersect_collinear(segs, s1, s2, affected)) {
changed = true;
}
} else {
Expand Down Expand Up @@ -302,16 +319,30 @@ struct scan_transition {
void snap_round(std::vector<segment> &segs) {
bool again = true;

// affected is indexed by segment instead of just segment index
// because fix_opposites() causes renumbering
std::set<segment> affected;

while (again) {
again = false;
std::set<segment> previously_affected = affected;
affected.clear();

#if 0
if (previously_affected.size() == 0) {
fprintf(stderr, "inspect %zu\n", segs.size());
} else {
fprintf(stderr, "reinspect %zu\n", previously_affected.size());
}
#endif

// find identical opposite-winding segments and adjust for them
//
// this is in the same loop because we may introduce new self-intersections
// in the course of trying to keep spindles alive, and will then need to
// resolve those.

if (fix_opposites(segs)) {
if (fix_opposites(segs, affected)) {
again = true;
}

Expand Down Expand Up @@ -357,16 +388,20 @@ void snap_round(std::vector<segment> &segs) {
for (size_t s1 : active) {
for (size_t s2 : active) {
if (s1 < s2) {
if (already.find(std::make_pair(s1, s2)) == already.end()) {
if (intersect(segs, s1, s2)) {
// if the segments intersected,
// we need to do another scan,
// because introducing a new node
// may have caused new intersections
again = true;
if (previously_affected.size() == 0 || // first time
previously_affected.count(segs[s1]) > 0 ||
previously_affected.count(segs[s2]) > 0) {
if (already.find(std::make_pair(s1, s2)) == already.end()) {
if (intersect(segs, s1, s2, affected)) {
// if the segments intersected,
// we need to do another scan,
// because introducing a new node
// may have caused new intersections
again = true;
}

already.insert(std::make_pair(s1, s2));
}

already.insert(std::make_pair(s1, s2));
}
}
}
Expand Down

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