ENH: improvements for vtkWrite function object (issue #926)

- parallel output.

  The output is now postProcessing/<name> for similar reasoning as
  mentioned in #866 - better alignment with other function objects, no
  collision with foamToVTK output.

- align the input parameters with those of vtkCloud so that we can
  specify the ASCII precision and the padding width for the output
  file names as well.

- emit TimeValue field, support file series generation

- support internal or boundary meshes, combining the result into a vtm
  file.

- can restrict conversion based on zone names, enclosing volumes,
  bounding box

tutorials/heatTransfer/chtMultiRegionFoam/multiRegionHeater/system/controlDict

@@ -52,4 +52,9 @@ maxDi           10.0;
 
 adjustTimeStep  yes;
 
+functions
+{
+    #include "vtkWrite"
+}
+
 // ************************************************************************* //

tutorials/heatTransfer/chtMultiRegionFoam/multiRegionHeater/system/vtkWrite

@@ -0,0 +1,62 @@
+// -*- C++ -*-
+// Use the vtkWrite function object
+
+vtkWrite
+{
+    type    vtkWrite;
+    libs    ("libutilityFunctionObjects.so");
+    log     true;
+
+    writeControl    writeTime;
+    writeInterval   1;
+
+    // Fields to output (words or regex)
+    regions (".*");
+
+    internal    true;
+
+    boundary    true;
+
+    single      false;
+
+    interpolate true;
+
+    // Fields to output (words or regex)
+    fields  (".*");
+
+    //- Output format (ascii | binary) - Default=binary
+    // format  binary;
+
+    //- Use legacy output format - Default=false
+    // legacy  false;
+
+    //- Output directory name - Default="postProcessing/<name>"
+    // directory   "VTK";
+
+    //- Write cell ids as field - Default=true
+    writeIds    false;
+}
+
+
+// Solid walls only
+walls
+{
+    type    vtkWrite;
+    libs    ("libutilityFunctionObjects.so");
+    log     true;
+
+    writeControl    writeTime;
+    writeInterval   1;
+
+    internal    false;
+
+    // single      true;
+
+    regions     ( heater "(?i).*solid" );
+    patches     ( "(?i).*solid_to.*" "heater.*(Air|Water)" );
+
+    fields      (T);
+}
+
+
+// ************************************************************************* //