Oops, was computing numerical by perturbing a point in uv; but the

xyz point that I subtracted off had been refined to lie exactly on
our edge's curve, and the uv point that I started with had not. So
normals got randomly screwed up.

[git-p4: depot-paths = "//depot/solvespace/": change = 1978]

solvespace.cpp

@@ -57,7 +57,7 @@ void SolveSpace::Init(char *cmdLine) {
     lightDir[1].y = CnfThawFloat( 0.0f, "LightDir_1_Up"        );
     lightDir[1].z = CnfThawFloat( 0.0f, "LightDir_1_Forward"   );
     // Chord tolerance
-    chordTol = CnfThawFloat(1.5f, "ChordTolerance");
+    chordTol = CnfThawFloat(2.0f, "ChordTolerance");
     // Max pwl segments to generate
     maxSegments = CnfThawDWORD(10, "MaxSegments");
     // View units

srf/boolean.cpp

@@ -276,7 +276,6 @@ void SSurface::EdgeNormalsWithinSurface(Point2d auv, Point2d buv,
     Point2d enuv = abuv.Normal();
 
     *pt    = PointAt(muv);
-    *surfn = NormalAt(muv.x, muv.y);
 
     // If this edge just approximates a curve, then refine our midpoint so
     // so that it actually lies on that curve too. Otherwise stuff like
@@ -288,8 +287,11 @@ void SSurface::EdgeNormalsWithinSurface(Point2d auv, Point2d buv,
         double t;
         sc->exact.ClosestPointTo(*pt, &t, false);
         *pt = sc->exact.PointAt(t);
+        ClosestPointTo(*pt, &muv);
     }
 
+    *surfn = NormalAt(muv.x, muv.y);
+
     // Compute the inner and outer normals of this edge (within the srf),
     // in xyz space. These are not necessarily antiparallel, if the
     // surface is curved.
@@ -487,7 +489,6 @@ void SShell::MakeIntersectionCurvesAgainst(SShell *agnst, SShell *into) {
             // list for into.
             sa->IntersectAgainst(sb, this, agnst, into);
         }
-        FLAG++;
     }
 }
 

util.cpp

@@ -510,8 +510,11 @@ Vector Vector::ScaledBy(double v) {
 Vector Vector::WithMagnitude(double v) {
     double m = Magnitude();
     if(m == 0) {
-        dbp("Vector::WithMagnitude of zero vector!");
-        return From(v, 0, 0);
+        // We can do a zero vector with zero magnitude, but not any other cases.
+        if(fabs(v) > 1e-100) {
+            dbp("Vector::WithMagnitude of zero vector!");
+        }
+        return From(0, 0, 0);
     } else {
         return ScaledBy(v/m);
     }