Question

Is it possible to replace the pattern of existing hatch objects without just deleting them and rehatching?

Answer

Yes it is possible. The following code demonstrates this:

  CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
  {
    CRhinoGetObject go;
    go.SetCommandPrompt( L"Select hatches to replace pattern" );
    go.SetGeometryFilter( CRhinoGetObject::hatch_object );
    go.GetObjects( 1, 0 );
    if( go.CommandResult() != success )
      return go.CommandResult();


    CRhinoGetString gs;
    gs.SetCommandPrompt( L"Name of replacement hatch pattern" );
    gs.GetString();
    if( gs.CommandResult() != success )
      return gs.CommandResult();


    ON_wString pattern_name = gs.String();
    pattern_name.TrimLeftAndRight();
    if( pattern_name.IsEmpty() )
      return nothing;


    int hatch_index = context.m_doc.m_hatchpattern_table.FindHatchPattern( pattern_name );
    if( hatch_index < 0 )
    {
      RhinoApp().Print( L"Specified hatch pattern not found in the document.\n" );
      return nothing;
    }


    int i, replaced = 0;
    for( i = 0; i < go.ObjectCount(); i++ )
    {
      const CRhinoHatch* hatch_obj = CRhinoHatch::Cast( go.Object(i).Object() );
      if( 0 == hatch_obj )
        continue;


      if( hatch_index == hatch_obj->PatternIndex() )
        continue;


      const ON_Hatch* hatch = hatch_obj->Hatch();
      if( 0 == hatch )
        continue;


      ON_Hatch* dup_hatch = hatch->DuplicateHatch();
      if( 0 == dup_hatch )
        continue;


      dup_hatch->SetPatternIndex( hatch_index );


      CRhinoHatch* dup_obj = hatch_obj->Duplicate();
      if( 0 == dup_obj )
      {
        delete dup_hatch;
        continue;
      }


      dup_obj->SetHatch( dup_hatch );
      if( !context.m_doc.ReplaceObject(CRhinoObjRef(hatch_obj), dup_obj) )
      {
        delete dup_obj;
        continue;
      }


      replaced++;
    }


    if( replaced > 0 )
    {
      context.m_doc.Redraw();
      if( 1 == replaced )
        RhinoApp().Print( L"1 hatch pattern replaced.\n" );
      else
        RhinoApp().Print( L"%d hatch patterns replaced.\n", replaced );
    }
    else
      RhinoApp().Print( L"0 hatch patterns replaced.\n" );


    return success;
  }