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Home < Documentation < 4.0 < Developers < Modules

For the latest Slicer developers documentation, visit the Nightly page.

Slicer 4 supports 3 types of modules. While the developer has to choose between one of the 3 types to implement its module, the end user won't notice a difference as they all share the look&feel. The choice for a given type of module is usually based on the type of inputs/parameters for a given module.

Command Line Interface (CLI)

CLIs are standalone executables with a limited input/output arguments complexity (simple argument types, no user interactions...). They are typically implemented using ITK. The recommended way to write your own CLI is to copy an existing module.

Loadable Modules

Loadable modules are C++ plugins that are built against Slicer. They define custom GUIs for their specific behavior as they have full control over the application.

Scripted Modules

Scripted modules are written in Python and typically but not necessarily use the high level API of Slicer and toolkits.

  • Python Console
  • Full access to the API: VTK, ITK, MRML, Qt and Slicer are fully wrapped
  • Recommended for fast prototyping
  • Links:

Module Factory

Loading modules into slicer happens in multiple steps:

  • module factories must be registered into the factory manager
  • directories where the modules to load are located must be passed to the factory manager
  • Optionally specify module names to ignore
  • scan the directories and test which file is a module and register it (not instantiated yet)
  • Instantiate all the register modules
  • Connect each module with the scene and the application

More details can be found in the online doc


  • Transform all core modules into Loadable modules.
    • the factory manager only support file based modules, core modules are not file based (linked into the core factory itself)
  • Move factory registration in qSlicerApplication (or a general application library) to support module discovery/loading without needing to instantiate Slicer.
    • Currently can't be moved into qSlicerApplication as the CLI factories that are in QTCLI depend on QTGUI
    • QtTesting is also limited with the QTCLI dependency on QtGUI (->qSlicerApplication would need to access QtTesting code from QtCli)
    • Proposed architecture
  Application -> classes that are useful to build an application (mix of qSlicerCoreApplication, qSlicerApplication, Main.cxx...)
  Core -> formally QtCore
  Modules -> contains the factories and module specific code
  Scripted -> all that is python specific
  Widgets -> formally QtGUI
  • Add category hierarchy in the Settings module panel
  • Register factory settings/command-options(e.g. disable-loadable-modules) when registering module factories
    • To have the settings panel be generic but have the code proper of each registered factory somewhere else
  • Add mechanism for modules to register dialogs (toolbars that open dialogs), e.g. the sceneview module needs to register the sceneView dialog into an icon.
  • Ignore modules from the launcher command line.