sbasis-to-bezier. avoid ill-conditioned behavior for anti-symmetric case. (Bug 1428267)

Fixed bugs:
  - https://launchpad.net/bugs/1428267

(bzr r14161)

1 files changed, 6 insertions, 0 deletions

diff --git a/src/2geom/sbasis-to-bezier.cpp b/src/2geom/sbasis-to-bezier.cpp
index a2e4253d2..98c400197 100644
--- a/src/2geom/sbasis-to-bezier.cpp
+++ b/src/2geom/sbasis-to-bezier.cpp
@@ -245,6 +245,8 @@ void sbasis_to_cubic_bezier (std::vector<Point> & bz, D2<SBasis> const& sb)
 
     midx = 8*midx - 4*bz[0][X] - 4*bz[3][X];  // re-define relative to center
     midy = 8*midy - 4*bz[0][Y] - 4*bz[3][Y];
+    if ((std::abs(midx) < EPSILON) && (std::abs(midy) < EPSILON))
+        return;
 
     if ((std::abs(xprime[0]) < EPSILON) && (std::abs(yprime[0]) < EPSILON)
     && ((std::abs(xprime[1]) > EPSILON) || (std::abs(yprime[1]) > EPSILON)))  { // degenerate handle at 0 : use distance of closest approach
@@ -264,6 +266,10 @@ void sbasis_to_cubic_bezier (std::vector<Point> & bz, D2<SBasis> const& sb)
         dely[1] = 0;
     } else if  (std::abs(xprime[1]*yprime[0] - yprime[1]*xprime[0]) >  // general case : fit mid fxn value
         0.002 * std::abs(xprime[1]*xprime[0] + yprime[1]*yprime[0])) { // approx. 0.1 degree of angle
+        double test1 = (bz[1][Y] - bz[0][Y])*(bz[3][X] - bz[0][X]) - (bz[1][X] - bz[0][X])*(bz[3][Y] - bz[0][Y]);
+        double test2 = (bz[2][Y] - bz[0][Y])*(bz[3][X] - bz[0][X]) - (bz[2][X] - bz[0][X])*(bz[3][Y] - bz[0][Y]);
+        if (test1*test2 < 0) // reject anti-symmetric case, LP Bug 1428267 & Bug 1428683
+            return;
         denom = xprime[1]*yprime[0] - yprime[1]*xprime[0];
         for (int i = 0; i < 2; ++i) {
             numer = xprime[1 - i]*midy - yprime[1 - i]*midx;