Initial functionality to write VTK FieldData

include/lean_vtk.hpp

@@ -9,6 +9,7 @@
 #include <iostream>
 #include <string>
 #include <vector>
+#include <tuple>
 
 namespace leanvtk {
 inline int index(int N, int i, int j) {
@@ -82,6 +83,14 @@ template <typename T> class VTKDataNode {
 
 class VTUWriter {
 public:
+
+  void add_field_data(const std::string& type,
+                      const std::string& name,
+                      const int& value);
+  void add_field_data(const std::string& type,
+                      const std::string& name,
+                      const double& value);
+
   /**
    * Write surface mesh to a file
    * const string& path             filename to store vtk mesh (ending with .vtu)
@@ -341,6 +350,9 @@ class VTUWriter {
   void clear();
 
 private:
+  typedef std::tuple<std::string,std::string,int,double> FieldDataTuple;
+
+  std::vector<FieldDataTuple> field_data_;
   std::vector<VTKDataNode<double>> point_data_;
   std::vector<VTKDataNode<double>> cell_data_;
   std::string current_scalar_point_data_;
@@ -356,6 +368,8 @@ class VTUWriter {
   void write_header(const int n_vertices, const int n_elements,
                     std::ostream &os);
 
+  void write_field_data(std::ostream &os);
+
   void write_footer(std::ostream &os);
 
   bool write_mesh(std::ostream &os, const int dim, const int cell_size,

src/lean_vtk.cpp

@@ -71,10 +71,62 @@ void VTUWriter::write_header(const int n_vertices, const int n_elements,
                              std::ostream &os) {
   os << "<VTKFile type=\"UnstructuredGrid\" version=\"1.0\">\n";
   os << "<UnstructuredGrid>\n";
+  write_field_data(os);
   os << "<Piece NumberOfPoints=\"" << n_vertices << "\" NumberOfCells=\""
      << n_elements << "\">\n";
 }
 
+//
+// per the VTK wiki, at https://vtk.org/Wiki/VTK/Tutorials/DataStorage
+//
+// "Arrays attached to the FieldData of a dataset describe global properties of
+//  the data. That is, if you want to save the time at which the data were
+//  recorded, you would put that value in the FieldData. If you wanted to name
+//  the data set, you would also put that in the FieldData. There are no
+//  restrictions about the length of arrays that are added to the FieldData."
+//
+void VTUWriter::add_field_data(const std::string& type,
+                               const std::string& name,
+                               const int& value) {
+    VTUWriter::FieldDataTuple t;
+    std::get<0>(t)=type;
+    std::get<1>(t)=name;
+    std::get<2>(t)=value;
+    field_data_.push_back(t);
+}
+void VTUWriter::add_field_data(const std::string& type,
+                               const std::string& name,
+                               const double& value) {
+    VTUWriter::FieldDataTuple t;
+    std::get<0>(t)=type;
+    std::get<1>(t)=name;
+    std::get<3>(t)=value;
+    field_data_.push_back(t);
+}
+void VTUWriter::write_field_data(std::ostream &os) {
+  if (field_data_.size()==0) {
+    return;
+  }
+  os << "<FieldData>\n";
+  for (auto t: field_data_) {
+    os << "<DataArray ";
+    std::string type=std::get<0>(t);
+    os << "type=\"" << type << "\" ";
+    os << "Name=\"" << std::get<1>(t) << "\" ";
+    os << "NumberOfTuples=\"1\" format=\"ascii\">\n";
+    // the data itself
+    if (type.find("Int")!=std::string::npos) {
+        os << std::get<2>(t) << "\n";
+    } else if (type.find("Float")!=std::string::npos) {
+        os << std::get<3>(t) << "\n";
+    } else {
+        os << "ERROR: field data type does not contain \"Int\" or \"Float\"\n";
+    }
+    os << "</DataArray>\n";
+  }
+  os << "</FieldData>\n";
+}
+
 void VTUWriter::write_footer(std::ostream &os) {
   os << "</Piece>\n";
   os << "</UnstructuredGrid>\n";
@@ -180,6 +232,7 @@ void VTUWriter::write_cell_data(std::ostream &os) {
   os << "</CellData>\n";
 }
 void VTUWriter::clear() {
+  field_data_.clear();
   point_data_.clear();
   cell_data_.clear();
 }

tests/test_lean_vtk.cpp

@@ -21,6 +21,9 @@ TEST_CASE("Single elements", "[single]"){
     int cell_size;
     std::string filename;
     bool is_volume_mesh = false;
+
+    VTUWriter writer;
+
     SECTION("Triangle 2D"){
         points = {
              1.,  1.,
@@ -112,6 +115,8 @@ TEST_CASE("Single elements", "[single]"){
         filename = "single_quad.vtu";
     }
     SECTION("Hex element"){
+        writer.add_field_data("Int32","CYCLE",123);
+        writer.add_field_data("Float64","TIME",4.56);
         points = {
              1.,  1., 1.,
              1., -1., 1.,
@@ -156,7 +161,6 @@ TEST_CASE("Single elements", "[single]"){
         filename = "single_tet.vtu";
         is_volume_mesh = true;
     }
-    VTUWriter writer;
 
     writer.add_scalar_field("scalar_field", scalar_field);
     writer.add_vector_field("vector_field", vector_field, dim);