Filter out degenerated triangles in STL export hotfix

See issue OpenFlipper-Free/OpenFlipper-Free#175

src/OpenMesh/Core/IO/writer/STLWriter.cc

@@ -134,6 +134,19 @@ write(std::ostream& _os, BaseExporter& _be, Options _opt, std::streamsize _preci
 
 //-----------------------------------------------------------------------------
 
+bool
+_STLWriter_::
+isDegeneratedTriangle(Vec3f& a, Vec3f& b, Vec3f& c) const {
+  Vec3f c1, c2;
+  for (int i=0;i<3;i++) {
+    if (i==0)      { c1=a; c2=b; }
+    else if (i==1) { c1=c;       }
+    else if (i==2) {       c2=a; }
+
+    if (c1[0] == c2[0] && c1[1] == c2[1] && c1[2] == c2[2]) return true;
+  }
+  return false;
+}
 
 bool
 _STLWriter_::
@@ -178,6 +191,11 @@ write_stla(const std::string& _filename, BaseExporter& _be, Options /* _opt */)
      _be.normal(fh) :
      ((c-b) % (a-b)).normalize());
 
+     if (isDegeneratedTriangle(a,b,c)) {
+       omlog() << "[STLWriter] : omitting degenerated triangle\n";
+       continue;
+     }
+
       fprintf(out, "facet normal %f %f %f\nouter loop\n", n[0], n[1], n[2]);
       fprintf(out, "vertex %.10f %.10f %.10f\n", a[0], a[1], a[2]);
       fprintf(out, "vertex %.10f %.10f %.10f\n", b[0], b[1], b[2]);

src/OpenMesh/Core/IO/writer/STLWriter.hh

@@ -102,6 +102,8 @@ private:
   bool write_stla(std::ostream&, BaseExporter&, Options, std::streamsize _precision = 6) const;
   bool write_stlb(const std::string&, BaseExporter&, Options) const;
   bool write_stlb(std::ostream&, BaseExporter&, Options, std::streamsize _precision = 6) const;
+
+  bool isDegeneratedTriangle(Vec3f& a, Vec3f& b, Vec3f& c) const;
 };