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Deal with horizontals

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This commit is contained in:
Erica Fischer
2023-11-10 09:28:24 -08:00
parent 35231d39e4
commit f6305b9b51
1 changed files with 51 additions and 2 deletions
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polygon.cpp
+51 -2
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@@ -70,7 +70,7 @@ void fix_opposites(std::vector<segment> &segs) {
segs.resize(out);
}
const std::pair<double, double> SAME_SLOPE = std::make_pair(INT_MAX, INT_MAX);
const std::pair<double, double> SAME_SLOPE = std::make_pair(-INT_MAX, INT_MAX);
// https://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect
//
@@ -117,6 +117,20 @@ bool vertical(std::vector<segment> &segs, size_t s, double y) {
return false;
}
bool horizontal(std::vector<segment> &segs, size_t s, double x) {
if ((x > std::round(segs[s].first.x) && x < std::round(segs[s].second.x)) ||
(x > std::round(segs[s].second.x) && x < std::round(segs[s].first.x))) {
double slope = (std::round(segs[s].second.y) - std::round(segs[s].first.y)) /
(std::round(segs[s].second.x) - std::round(segs[s].first.x));
double y = std::round(std::round(segs[s].first.y) + slope * (x - std::round(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));
return true;
}
return false;
}
bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
bool changed = false;
@@ -149,7 +163,42 @@ bool intersect_collinear(std::vector<segment> &segs, size_t s1, size_t s2) {
exit(EXIT_IMPOSSIBLE);
}
} else {
// XXX not vertical
// horizontal or diagonal
double slope1 = (std::round(segs[s1].second.y) - std::round(segs[s1].first.y)) /
(std::round(segs[s1].second.x) - std::round(segs[s1].first.x));
double slope2 = (std::round(segs[s2].second.y) - std::round(segs[s2].first.y)) /
(std::round(segs[s2].second.x) - std::round(segs[s2].first.x));
if (slope1 == slope2) {
// they are parallel. do they have the same y intercept?
double y1 = std::round(std::round(segs[s1].first.y) + slope1 * (0 - std::round(segs[s1].first.x)));
double y2 = std::round(std::round(segs[s2].first.y) + slope1 * (0 - std::round(segs[s2].first.x)));
if (y1 == y2) {
// collinear, not parallel
if (horizontal(segs, s1, std::round(segs[s2].first.x))) {
changed = true;
}
if (horizontal(segs, s1, std::round(segs[s2].second.x))) {
changed = true;
}
if (horizontal(segs, s2, std::round(segs[s1].first.x))) {
changed = true;
}
if (horizontal(segs, s2, std::round(segs[s1].second.x))) {
changed = true;
}
}
} else {
fprintf(stderr, "One segment has a slope of %f and the other %f: %f,%f to %f,%f; %f,%f to %f,%f.\n",
slope1, slope2,
segs[s1].first.x, segs[s1].first.y, segs[s1].second.x, segs[s1].second.y,
segs[s2].first.x, segs[s2].first.y, segs[s2].second.x, segs[s2].second.y);
exit(EXIT_IMPOSSIBLE);
}
}
return changed;