Documentation/4.0/Developers/Modules

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.

• Shared lib or executable
• GUI automatically generated
• Links:
  • Slicer3 execution model (Slicer4 is very similar)
  • CLI in Slicer4 (presentation of 2012 NAMIC AHM)

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.

• C++ shared library
• Full control over the GUI (Qt) and Slicer internals (MRML, logics, display managers...)
• Optimized for heavy computations
• Links:
  • Loadable modules (presentation of 2012 NAMIC AHM)
  • How to write a loadable module

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:
  • Scripting

Module Factory

Loading modules into slicer happens in multiple steps:

• module factories must be registered into the factory manager:

qSlicerModuleFactoryManager* factoryManager = app->moduleManager()->factoryManager();
factoryManager->registerFactory(new qSlicerLoadableModuleFactory);
...

• directories where the modules to load are located must be passed to the factory manager

factoryManager->addSearchPath(app->slicerHome() + "/" +  Slicer_QTSCRIPTEDMODULES_LIB_DIR + "/" );
factoryManager->addSearchPath(app->slicerHome() + "/" + Slicer_CLIMODULES_LIB_DIR + "/" );
...

• Optionally specify module names to ignore

For startup speed-up and memory consummation, it can be useful to not load some modules

factoryManager->setModulesToSkip(QStringList(QString("Data")));

• scan the directories and test which file is a module and register it (not instantiated yet)

For each file in the search paths, the factory manager asks each registered factory if they can load the file. If there is a factory that supports the file, the manager associates the factory to the file path, otherwise the file is discarded.

factoryManager->registerModules();

• Instantiate all the register modules

factoryManager->instantiateModules();

• Connect each module with the scene and the application

The application logic and the scene are passed to each module. The order of initialization is defined with the dependencies of the modules. If module B depends of module A, it is assured that module B is initialized/setup after A.

factoryManager->loadModules();

ToDo

• 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 are in QTCl that depends on QTGUI
  • Proposed architecture

Base
  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
     Loadable
     CLI
     Scripted
  Scripted -> all that is python specific
     Cxx
     Python
  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.