The following source code sample demonstrates how to synchronize the basic material color of an object with the display color of the object. If the object does not have a material assigned to it, a new material is created and assigned to the object.

C++

  CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
  {
    int num_modified = 0;
    CRhinoObjectIterator it( CRhinoObjectIterator::normal_objects, 
                             CRhinoObjectIterator::active_objects );
    it.IncludeLights( FALSE );


    CRhinoObject* obj = 0;
    for( obj = it.First(); obj; obj = it.Next() )
    {
      // If the object gets its color from its layer, then we will
      // let the layer handle its material color as well.
      ON::object_color_source color_source = obj->Attributes().ColorSource();
      if( color_source != ON::color_from_object ) 
        continue;


      int material_index = obj->Attributes().m_material_index;
      if( material_index < 0 )
      {
        // If material_index < 0, then the object does not have a 
        // material assigned to it. So, we will create a new material
        // that is based on Rhino's default material, and add it
        // to the material table.
        ON_Material material( RhinoApp().AppSettings().DefaultMaterial() );
        material_index = context.m_doc.m_material_table.AddMaterial( material );
        if( material_index >= 0 )
        {
          // Now that we have added the new material,
          // assign it to the object.
          CRhinoObjectAttributes new_attributes( obj->Attributes() );
          new_attributes.m_material_index = material_index;
          // Make sure to set the material source to "from object"
          new_attributes.SetMaterialSource( ON::material_from_object );
          obj->ModifyAttributes( new_attributes );
        }
      }
      if( material_index < 0 )
        continue;


      const CRhinoMaterial& material = context.m_doc.m_material_table[material_index];
      if( obj->Attributes().DrawColor() == material.Diffuse() )
        continue;


      // Modify the material's basic,or diffuse, color
      ON_Material new_material( material );
      new_material.SetDiffuse( obj->Attributes().DrawColor() );
      context.m_doc.m_material_table.ModifyMaterial( new_material,
                                                     material.MaterialIndex(),
                                                     FALSE );
      num_modified++;
    }


    if( num_modified > 0 )
      context.m_doc.Regen();


    return CRhinoCommand::success;
  }

VB.NET (Rhino 4)

  Public Overrides Function RunCommand(ByVal context As IRhinoCommandContext) _
    As RMA.Rhino.IRhinoCommand.result


    Dim num_modified As Integer = 0
    Dim it As New MRhinoObjectIterator( _
        IRhinoObjectIterator.object_state.normal_objects, _
        IRhinoObjectIterator.object_category.active_objects)
    it.IncludeLights(False)


    For Each obj As MRhinoObject In it
      ' If the object gets its color from its layer, then we will
      ' let the layer handle its material color as well.
      Dim color_source As IOn.object_color_source = obj.Attributes().ColorSource()
      If (color_source <> IOn.object_color_source.color_from_object) Then
        Continue For
      End If


      Dim material_index As Integer = obj.Attributes().m_material_index
      If (material_index < 0) Then
        ' If material_index < 0, then the object does not have a 
        ' material assigned to it. So, we will create a new material
        ' that is based on Rhino's default material, and add it
        ' to the material table.
        Dim mat As New OnMaterial(RhUtil.RhinoApp().AppSettings().DefaultMaterial())
        material_index = context.m_doc.m_material_table.AddMaterial(mat)
        If (material_index >= 0) Then
          ' Now that we have added the new material, assign it to the object.
          Dim new_attributes As New MRhinoObjectAttributes(obj.Attributes())
          new_attributes.m_material_index = material_index
          ' Make sure to set the material source to "from object"
          new_attributes.SetMaterialSource(IOn.object_material_source.material_from_object)
          obj.ModifyAttributes(new_attributes)
        End If
      End If


      If (material_index < 0) Then Continue For


      Dim material As IRhinoMaterial = context.m_doc.m_material_table(material_index)
      If (obj.Attributes().DrawColor().Compare(material.m_diffuse) = 0) Then Continue For


      ' Modify the material's basic,or diffuse, color
      Dim new_material As New OnMaterial(material)
      new_material.m_diffuse = obj.Attributes().DrawColor()
      context.m_doc.m_material_table.ModifyMaterial( new_material, _
                                                     material.m_material_index, _
                                                     False)
      num_modified = num_modified + 1
    Next


    If (num_modified > 0) Then context.m_doc.Regen()
    Return IRhinoCommand.result.success
  End Function

C# (Rhino 4)

  public override IRhinoCommand.result RunCommand(IRhinoCommandContext context)
  {
    int num_modified = 0;
    MRhinoObjectIterator it = new MRhinoObjectIterator(
        IRhinoObjectIterator.object_state.normal_objects, 
        IRhinoObjectIterator.object_category.active_objects);
    it.IncludeLights(false);


    foreach (MRhinoObject obj in it)
    {
      // If the object gets its color from its layer, then we will
      // let the layer handle its material color as well.
      IOn.object_color_source color_source = obj.Attributes().ColorSource();
      if(color_source != IOn.object_color_source.color_from_object)
        continue;


      int material_index = obj.Attributes().m_material_index;
      if(material_index < 0)
      {
        // If material_index < 0, then the object does not have a 
        // material assigned to it. So, we will create a new material
        // that is based on Rhino's default material, and add it
        // to the material table.
        OnMaterial mat = new OnMaterial(RhUtil.RhinoApp().AppSettings().DefaultMaterial());
        material_index = context.m_doc.m_material_table.AddMaterial(mat);
        if(material_index >= 0)
        {
          // Now that we have added the new material, assign it to the object.
          MRhinoObjectAttributes new_attrib = 
                  new MRhinoObjectAttributes(obj.Attributes());
          new_attrib.m_material_index = material_index;
          // Make sure to set the material source to "from object"
          new_attrib.SetMaterialSource(IOn.object_material_source.material_from_object);
          obj.ModifyAttributes(new_attrib);
        }
      }


      if(material_index < 0)
        continue;


      IRhinoMaterial material = context.m_doc.m_material_table[material_index];
      if(obj.Attributes().DrawColor().Compare(material.m_diffuse) == 0)
        continue;


      // Modify the material's basic,or diffuse, color
      OnMaterial new_material = new OnMaterial(material);
      new_material.m_diffuse = obj.Attributes().DrawColor();
      context.m_doc.m_material_table.ModifyMaterial(new_material,
                                                    material.m_material_index,
                                                    false);
      num_modified++;
    }


    if (num_modified > 0)
      context.m_doc.Regen();
    return IRhinoCommand.result.success;
  }