Finding an Annotation object's font

This guide demonstrates how to get an Annotation object's font using openNURBS.


There are many changes to ONX_Model in openNURBS. In prior versions, I was getting the font and its id information for ON_Leader2 with:

ONX_Model model = ...
const ON_Leader2* leader = ...
const ON_Font& font = model.m_font_table[leader->Index()];

How can I do this with the current openNURBS?


In openNURBS, the the dimension style, or ON_DimStyle, specifies all appearance properties like the text font, size, and alignment, arrow head shape, and so on. To obtain the font used by an Annotation object, such as an ON_Leader, you just need to query the object’s effective dimension style.


The following example code can be used to get the ON_Font used by an ON_Leader using the openNURBS toolkit:

ONX_Model model = ...

// Create a model geometry interator
ONX_ModelComponentIterator it(model, ON_ModelComponent::Type::ModelGeometry);
const ON_ModelComponent* model_component = nullptr;
for (model_component = it.FirstComponent(); nullptr != model_component; model_component = it.NextComponent())
  // Get the model geometry
  const ON_ModelGeometryComponent* model_geometry = ON_ModelGeometryComponent::Cast(model_component);
  if (nullptr == model_geometry)

  // Try getting an annotation leader
  const ON_Leader* leader = ON_Leader::Cast(model_geometry->Geometry(nullptr));
  if (nullptr == leader)

  // Get the parent dimension style
  const ON_ModelComponentReference& parent_dim_style_ref = model.DimensionStyleFromId(leader->DimensionStyleId());
  const ON_DimStyle* parent_dim_style = ON_DimStyle::Cast(parent_dim_style_ref.ModelComponent());
  if (nullptr == parent_dim_style)
  // Get the effective dimension style
  const ON_DimStyle& dim_style = leader->DimensionStyle(*parent_dim_style);

  // Get the font
  const ON_Font& font = dim_style.Font();

  // TODO...