Fix for stroke rendering instability with stroke geometry shaders.

* Stroke::Resample(int nPoints) was not properly working when a wrong
value was returned from Stroke::getLength2D(), resulting in repeated
warning messages "Warning: incorrect points number" during stroke
rendering.  The main cause was that stroke geometry shaders did not
update the two-dimensional (2D) length (also referred to as curvilinear
abscissa) after they modified the 2D points of stroke vertices.  Now
all stroke geometry shaders make explicit calls for Stroke::UpdateLength()
that has been introduced for recomputing the 2D length.  Many thanks to
Josef who reported the problem together with sample .blend files for
reproducing the issue.

* Missing Python wrapper of Stroke::getLength2D() was added.

3 files changed, 18 insertions, 24 deletions

diff --git a/source/blender/freestyle/intern/stroke/BasicStrokeShaders.cpp b/source/blender/freestyle/intern/stroke/BasicStrokeShaders.cpp
index bc9edcef057..ec9f887d533 100755
--- a/source/blender/freestyle/intern/stroke/BasicStrokeShaders.cpp
+++ b/source/blender/freestyle/intern/stroke/BasicStrokeShaders.cpp
@@ -586,6 +586,8 @@ namespace StrokeShaders {
     (v0)->setPoint(newFirst[0], newFirst[1]);
     Vec2d newLast(last+_amount*dn);
     (vn)->setPoint(newLast[0], newLast[1]);
+
+	stroke.UpdateLength();
 	return 0;
   }
 
@@ -611,6 +613,7 @@ namespace StrokeShaders {
 	sv->setPoint(newPoint[0], newPoint[1]);
 	++it;
       }
+	stroke.UpdateLength();
 	return 0;
   }
 
@@ -726,6 +729,7 @@ namespace StrokeShaders {
 	++it;
 	++n;
       }
+	stroke.UpdateLength();
 	return 0;
   }
 
@@ -844,6 +848,7 @@ namespace StrokeShaders {
 	++p;
 	++n;
       }
+	stroke.UpdateLength();
 
     // Deal with extra vertices:
     if(nExtraVertex == 0)
@@ -931,6 +936,7 @@ namespace StrokeShaders {
 	sv->setPoint(newPoint[0], newPoint[1]);
 	++it;
       }
+	stroke.UpdateLength();
 	return 0;
   }
 
@@ -1038,6 +1044,7 @@ namespace StrokeShaders {
 	//    u.normalize();
 	//    (*a)->setPoint((*a)->x()-u.x()*10, (*a)->y()-u.y()*10);
       }
+	stroke.UpdateLength();
 
     // delete stuff
     for(cp=_results.begin(), cpend=_results.end();
@@ -1076,6 +1083,7 @@ namespace StrokeShaders {
       {
 	v->setPoint(piece.A.x()+v->u()*u.x()+n.x()*offset, piece.A.y()+v->u()*u.y()+n.y()*offset);
       }
+	stroke.UpdateLength();
 	return 0;
   }
 
diff --git a/source/blender/freestyle/intern/stroke/Stroke.cpp b/source/blender/freestyle/intern/stroke/Stroke.cpp
index f6cefdfee34..0c852d0e209 100755
--- a/source/blender/freestyle/intern/stroke/Stroke.cpp
+++ b/source/blender/freestyle/intern/stroke/Stroke.cpp
@@ -674,28 +674,7 @@ void Stroke::RemoveVertex(StrokeVertex *iVertex)
       break;
     }
   }
-  // recompute various values (length, curvilign abscissa)
-  float curvabsc = 0.f;
-  it=_Vertices.begin();
-  itend=_Vertices.end();
-  vertex_container::iterator previous=it;
-  for(;
-  (it!=itend);
-  ++it)
-  {
-    if(it != previous)
-      curvabsc += ((*it)->point2d()-(*previous)->point2d()).norm();
-    (*it)->setCurvilinearAbscissa(curvabsc);
-    previous = it;
-  }
-  _Length = curvabsc;
-  it=_Vertices.begin();
-  for(;
-  (it!=itend);
-  ++it)
-  {
-    (*it)->setStrokeLength(_Length);
-  }
+  UpdateLength();
 }
 
 void Stroke::InsertVertex(StrokeVertex *iVertex, StrokeInternal::StrokeVertexIterator next)
@@ -704,10 +683,14 @@ void Stroke::InsertVertex(StrokeVertex *iVertex, StrokeInternal::StrokeVertexIte
 
   vertex_container::iterator itnext = next.getIt();
   _Vertices.insert(itnext, iVertex);
+  UpdateLength();
+}
+
+void Stroke::UpdateLength()
+{
   // recompute various values (length, curvilign abscissa)
   float curvabsc = 0.f;
-  it=_Vertices.begin();
-  itend=_Vertices.end();
+  vertex_container::iterator it=_Vertices.begin(), itend=_Vertices.end();
   vertex_container::iterator previous=it;
   for(;
   (it!=itend);
diff --git a/source/blender/freestyle/intern/stroke/Stroke.h b/source/blender/freestyle/intern/stroke/Stroke.h
index 5e0974edea7..1b1084b54c2 100755
--- a/source/blender/freestyle/intern/stroke/Stroke.h
+++ b/source/blender/freestyle/intern/stroke/Stroke.h
@@ -466,6 +466,9 @@ public:
    */
   void InsertVertex(StrokeVertex *iVertex, StrokeInternal::StrokeVertexIterator next);
 
+  /*! Updates the 2D length of the Stroke */
+  void UpdateLength();
+
   /* Render method */
   void Render(const StrokeRenderer *iRenderer );
   void RenderBasic(const StrokeRenderer *iRenderer );