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svg-flatten: Fix hang in dehole_polytree

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previously, dehole_polytree could hang for certain inputs containing
concave holes.
This commit is contained in:
jaseg 2024-09-23 20:38:27 +02:00
parent f50c4f8172
commit 00f0d772f7
1 changed files with 64 additions and 6 deletions
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70
svg-flatten/src/svg_geom.cpp
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@ -91,6 +91,64 @@ enum ClipperLib::JoinType gerbolyze::clipper_join_type(const pugi::xml_node &nod
return ClipperLib::jtMiter;
}
/* Some debugging helpers */
static double toplevel_winding_direction(PolyNode &ptree) {
double sum = 0.0;
size_t sz = ptree.Contour.size();
for (size_t i=0; i<sz; i++) {
size_t j = (i+1) % sz;
double x1 = ptree.Contour[i].X, y1 = ptree.Contour[i].Y;
double x2 = ptree.Contour[j].X, y2 = ptree.Contour[j].Y;
sum += (x2-x1)*(y2+y1);
}
return sum;
}
static void dump_ptree(PolyNode &ptree) {
/* dumps node count, winding direction and tree structure */
double sum = toplevel_winding_direction(ptree);
char sign = '.';
if (sum > 0) {
sign = '+';
} else if (sum < 0) {
sign = '-';
}
cerr << sign << ptree.Contour.size() << "[";
for (size_t i=0; i<ptree.ChildCount(); i++) {
if (i > 0) {
cerr << ",";
}
dump_ptree(*ptree.Childs[i]);
}
cerr << "]";
}
static void dump_clipper2svg(Path &path, string stroke) {
/* dumps the ptree to SVG */
/* use together with
cerr << "<svg width=\"200\" height=\"200\" xmlns=\"http://www.w3.org/2000/svg\">" << endl;
...
dump_clipper2svg(...); // can be used multiple times
...
cerr << "</svg>" << endl;
*/
size_t sz = path.size();
if (sz == 0) {
return;
}
cerr << "<path fill=\"" << stroke << "\" d=\"M ";
for (size_t i=0; i<sz; i++) {
if (i>0) {
cerr << " L ";
}
cerr << (path[i].X / 1e7) << ", " << (path[i].Y / 1e7);
}
cerr << " Z\"/>" << endl;
}
static void dehole_polytree_worker(PolyNode &ptree, Paths &out, queue<PolyTree> &todo) {
for (int i=0; i<ptree.ChildCount(); i++) {
PolyNode *nod = ptree.Childs[i];
@ -127,21 +185,21 @@ static void dehole_polytree_worker(PolyNode &ptree, Paths &out, queue<PolyTree>
* until we find a point that has a different X coordinate than our starting point. If we can't find one
* because the polygon only consists only of points on a vertical line, we can safely discard it and do
* nothing since it has zero area anyway. */
for (size_t i=0; i<nod->Childs[0]->Contour.size(); i++) {
if (nod->Childs[0]->Contour[i].X == nod->Childs[0]->Contour[0].X) {
for (size_t i=1; i<nod->Childs[0]->Contour.size(); i++) {
if (nod->Childs[0]->Contour[i].X == nod->Childs[0]->Contour[i-1].X) {
continue;
}
/* We now have found that Contour[0] - Contour[i] has a non-zero horizontal component, and is a
/* We now have found that Contour[i-1] - Contour[i] has a non-zero horizontal component, and is a
* candidate for our cut. However, we have to make sure that the first point is left (lower X
* coordinate) of the second point, or the cutting polygon we create here would have a
* self-intersection, which with high likelihood would lead to a new hole being created when cutting.
*/
int a=0, b=i;
if (nod->Childs[0]->Contour[i].X < nod->Childs[0]->Contour[0].X) {
int a=i-1, b=i;
if (nod->Childs[0]->Contour[i].X < nod->Childs[0]->Contour[i-1].X) {
/* Swap points */
a = i;
b = 0;
b = i-1;
}
Path tri = { { bbox.left, bbox.top }, nod->Childs[0]->Contour[a], nod->Childs[0]->Contour[b], { bbox.right, bbox.top } };
c.AddPath(tri, ptClip, true);