For a editor VP solution see Custom show flag

Component Visualizer

There is a struct called FComponentVisualizer that seems to be used to draw/debug whatever you want for a specific component class.

See FConstraintComponentVisualizer::DrawVisualization and FComponentVisualizersModule::StartupModule for an example.

See zomg’s post for the base setup.

About GUnrealEd in StartupModule

As I found here GUnrealEd is null in StartupModule if you are loading it to early. Load your module at PostEngineInit phase to correct that. Or use the following delegate: FCoreDelegates::OnPostEngineInit.AddRaw(this, &FMyModule::OnPostEngineInit);

More details about it (with an example on Unity box collider 6 faces maker) here

Component visualizer’s are used in UUnrealEdEngine::DrawComponentVisualizers, see also FSCSEditorViewportClient::Draw