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Fix #693 issues. 

This set of changes covers all triangulation errors in issue 693. A point coincident with a triangle vertex is OK and needed for bridges, but sometimes the middle point has edges cutting through the triangle that make it a non-ear. We fix that and a couple of off-by-one error (that fixes one of the test cases).
pull/697/head
phkahler 2020-09-08 13:20:12 -04:00
parent 0413c1b926
commit 705249627a
1 changed files with 39 additions and 3 deletions
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42
src/srf/triangulate.cpp
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@ -124,7 +124,7 @@ bool SContour::BridgeToContour(SContour *sc,
// to the leftmost point of the new segment.
int thiso = 0;
double dmin = 1e10;
for(i = 0; i < l.n; i++) {
for(i = 0; i < l.n-1; i++) {
Vector p = l[i].p;
double d = (p.Minus(sc->xminPt)).MagSquared();
if(d < dmin) {
@ -140,7 +140,7 @@ bool SContour::BridgeToContour(SContour *sc,
// First check if the contours share a point; in that case we should
// merge them there, without a bridge.
for(i = 0; i < l.n; i++) {
thisp = WRAP(i+thiso, l.n);
thisp = WRAP(i+thiso, l.n-1);
a = l[thisp].p;
for(f = avoidPts->First(); f; f = avoidPts->NextAfter(f)) {
@ -256,6 +256,28 @@ bool SContour::IsEmptyTriangle(int ap, int bp, int cp, double scaledEPS) const {
return true;
}
// Test if ray b->d passes through triangle a,b,c
static bool RayIsInside(Vector a, Vector c, Vector b, Vector d) {
// coincident edges are not considered to intersect the triangle
if (d.Equals(a)) return false;
if (d.Equals(c)) return false;
// if d and c are on opposite sides of ba, we are ok
// likewise if d and a are on opposite sides of bc
Vector ba = a.Minus(b);
Vector bc = c.Minus(b);
Vector bd = d.Minus(b);
// perpendicular to (x,y) is (x,-y) so dot that with the two points. If they
// have opposite signs their product will be negative. If bd and bc are on
// opposite sides of ba the ray does not intersect. Likewise for bd,ba and bc.
if ( (bd.x*(ba.y) + (bd.y * (-ba.x))) * ( bc.x*(ba.y) + (bc.y * (-ba.x))) < LENGTH_EPS)
return false;
if ( (bd.x*(bc.y) + (bd.y * (-bc.x))) * ( ba.x*(bc.y) + (ba.y * (-bc.x))) < LENGTH_EPS)
return false;
return true;
}
bool SContour::IsEar(int bp, double scaledEps) const {
int ap = WRAP(bp-1, l.n),
cp = WRAP(bp+1, l.n);
@ -294,8 +316,19 @@ bool SContour::IsEar(int bp, double scaledEps) const {
// and therefore makes it a non-ear; but a point on the vertex is
// "outside", since that's necessary to make bridges work.
if(p.EqualsExactly(tr.a)) continue;
if(p.EqualsExactly(tr.b)) continue;
if(p.EqualsExactly(tr.c)) continue;
// points coincident with bp have to be allowed for bridges but edges
// from that other point must not cross through our triangle.
if(p.EqualsExactly(tr.b)) {
int j = WRAP(i-1, l.n);
int k = WRAP(i+1, l.n);
Vector jp = l[j].p;
Vector kp = l[k].p;
// check both edges from the point in question
if (!RayIsInside(tr.a, tr.c, p,jp) && !RayIsInside(tr.a, tr.c, p,kp))
continue;
}
if(tr.ContainsPointProjd(n, p)) {
return false;
@ -349,6 +382,9 @@ void SContour::UvTriangulateInto(SMesh *m, SSurface *srf) {
l[i].tag = 1;
}
}
if( (l[0].p).Equals(l[l.n-1].p) ) {
l[l.n-1].tag = 1;
}
l.RemoveTagged();
// Handle simple triangle fans all at once. This pass is optional.