Bug fixes from Stéphane Grabli, one of the coauthors of the

original Freestyle:

* Fix for making the stroke construction more robust to nearly
overlapping vertices.

* Fix for a bug in the computation of the occluded surfaces.

These changes make the visibility computation more robust and
the line quality generally higher.

2 files changed, 31 insertions, 8 deletions

diff --git a/source/blender/freestyle/intern/stroke/Operators.cpp b/source/blender/freestyle/intern/stroke/Operators.cpp
index ef1b2662998..ea996c67785 100755
--- a/source/blender/freestyle/intern/stroke/Operators.cpp
+++ b/source/blender/freestyle/intern/stroke/Operators.cpp
@@ -938,10 +938,18 @@ Stroke* createStroke(Interface1D& inter) {
       stroke_vertex = new StrokeVertex(cp);
     current = stroke_vertex->point2d();
     Vec3r vec_tmp(current - previous);
-    currentCurvilignAbscissa += vec_tmp.norm();
-    stroke_vertex->setCurvilinearAbscissa(currentCurvilignAbscissa);
-    stroke->push_back(stroke_vertex);
-    previous = current;
+    real vec_tmp_norm = vec_tmp.norm();
+    if((stroke->strokeVerticesSize() > 0) && (vec_tmp_norm < 1.e-06)){
+      // The point we just created is superimposed with the 
+      // previous one. We remove it to avoid having to deal
+      // with this kind of singularities in the strip creation
+      delete stroke_vertex;
+    }else{
+      currentCurvilignAbscissa += vec_tmp.norm();
+      stroke_vertex->setCurvilinearAbscissa(currentCurvilignAbscissa);
+      stroke->push_back(stroke_vertex);
+      previous = current;
+    }
     ++it;
   } while((it != itend) && (it != itfirst));
 
@@ -959,9 +967,17 @@ Stroke* createStroke(Interface1D& inter) {
       stroke_vertex = new StrokeVertex(cp);
     current = stroke_vertex->point2d();
     Vec3r vec_tmp(current - previous);
-    currentCurvilignAbscissa += vec_tmp.norm();
-    stroke_vertex->setCurvilinearAbscissa(currentCurvilignAbscissa);
-    stroke->push_back(stroke_vertex);
+    real vec_tmp_norm = vec_tmp.norm();
+    if((stroke->strokeVerticesSize() > 0) && (vec_tmp_norm < 1.e-06)){
+      // The point we just created is superimposed with the 
+      // previous one. We remove it to avoid having to deal
+      // with this kind of singularities in the strip creation
+      delete stroke_vertex;
+    }else{
+      currentCurvilignAbscissa += vec_tmp.norm();
+      stroke_vertex->setCurvilinearAbscissa(currentCurvilignAbscissa);
+      stroke->push_back(stroke_vertex);
+    }
   }
   stroke->setLength(currentCurvilignAbscissa);
   return stroke;
diff --git a/source/blender/freestyle/intern/stroke/StrokeRep.cpp b/source/blender/freestyle/intern/stroke/StrokeRep.cpp
index fbe1273bac0..6ae15c71833 100755
--- a/source/blender/freestyle/intern/stroke/StrokeRep.cpp
+++ b/source/blender/freestyle/intern/stroke/StrokeRep.cpp
@@ -254,7 +254,14 @@ Strip::createStrip (const vector<StrokeVertex*>& iStrokeVertices)
       else 
         _vertices.push_back(new StrokeVertexRep(p-thickness[0]*stripDir));
       ++i;
-		
+
+      if((stripDir+stripDirPrev).norm() <= 1.e-06){
+        // the strip is most likely doing a U-turn, we can't compute the average vector.
+        // We just continue and hope it's ok
+        vPrev = v;
+        continue;
+      }
+      
       // if the angle is obtuse, we simply average the directions to avoid the singularity
       stripDir=stripDir+stripDirPrev;
       if ((dirNorm<ZERO) || (dirPrevNorm<ZERO) || (stripDir.norm() < ZERO)) {