From 0f320aa6710d60e2940432d07757ef91d835e19c Mon Sep 17 00:00:00 2001
From: alemuntoni <muntoni.alessandro@gmail.com>
Date: Tue, 6 Jul 2021 16:43:22 +0200
Subject: [PATCH] fix off polygon export

---
 vcg/complex/algorithms/polygon_support.h | 7 +++++--
 wrap/io_trimesh/export_off.h             | 9 ++++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/vcg/complex/algorithms/polygon_support.h b/vcg/complex/algorithms/polygon_support.h
index bce0d219..801a35bb 100644
--- a/vcg/complex/algorithms/polygon_support.h
+++ b/vcg/complex/algorithms/polygon_support.h
@@ -24,6 +24,9 @@
 #ifndef __VCGLIB_POLYGON_SUPPORT
 #define __VCGLIB_POLYGON_SUPPORT
 
+#include <vcg/complex/allocate.h>
+#include <vcg/complex/base.h>
+#include <vcg/complex/algorithms/update/flag.h>
 #include <vcg/simplex/face/jumping_pos.h>
 #include <vcg/space/planar_polygon_tessellation.h>
 
@@ -141,8 +144,8 @@ namespace tri {
         {
             std::vector<typename TriMeshType::VertexPointer> vs;// vertices of the polygon
             ExtractPolygon(&*tfi,vs);
-			if (vs.size() > 3)
-				std::reverse(vs.begin(), vs.end());
+            if (vs.size() > 3)
+              std::reverse(vs.begin(), vs.end());
             //now vs  contains all the vertices of the polygon (still in the trimesh)
             if (vs.size()==0)continue;
             typename PolyMeshType::FaceIterator pfi =  tri::Allocator<PolyMeshType>::AddFaces(pm,1);
diff --git a/wrap/io_trimesh/export_off.h b/wrap/io_trimesh/export_off.h
index 3a9fec97..d4b8435b 100644
--- a/wrap/io_trimesh/export_off.h
+++ b/wrap/io_trimesh/export_off.h
@@ -104,10 +104,17 @@ public:
       tri::UpdateFlags<SaveMeshType>::FaceClearV(m);
       for(FaceIterator fi=m.face.begin();fi!=m.face.end();++fi) if (!fi->IsD()) if (!fi->IsV()) {
         vcg::tri::PolygonSupport<SaveMeshType,SaveMeshType>::ExtractPolygon(&*fi,polygon);
+        //not sure why this std::reverse is needed. ExtractPolygon is used in
+        //many other functions, and nobody complained. however, this list is
+        //clockwise wrt fi normal.
+        std::reverse(polygon.begin(), polygon.end());
         if(!polygon.empty())
         {
           fprintf(fpout,"%d ", int(polygon.size()) );
-          for (size_t i=0; i<polygon.size(); i++) fprintf(fpout,"%d ", polygon[i]->Flags() );
+          for (size_t i=0; i<polygon.size(); i++)
+            fprintf(fpout,"%lu ", tri::Index(m,polygon[i]));
+          if( tri::HasPerFaceColor(m)  && (mask & io::Mask::IOM_FACECOLOR) )
+            fprintf(fpout,"%i %i %i", fi->C()[0],fi->C()[1],fi->C()[2] );
           fprintf(fpout,"\n");
         }
       }