Projects:ARRA:SlicerEM:Developer:WorkflowManager

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Summary

• EMSegmenter has a fairly complicated workflow
• Need a mechanism to validate user input and transition appropriately between steps of the workflow
• Should be dependent on Qt only (and not VTK)
• Current plan (subject to change) = use Qt's state machine implementation, with our own workflow manager on top (Qt Wizard doesn't quite work in harmony with the Qt state machine framework, and the UI itself can't be embedded in a pre-existing top-level)

Previous workflow manager implementation in KWWidgets

• Please see the documentation here, as it is already well described

Uses:

• KWWidgets state machines - incorporates states (ex. user interaction within a workflow step, validation of the user input within a workflow step), transitions (between states), and inputs (pushed onto a queue to trigger transitions)
• KWWidgets wizard workflow - provides additional functionality to manage workflow using a state machine (ex. bundles pairs of user interaction and validation states into a workflow "step", handles a navigation stack of steps encountered along the way that triggers updates of widgets and/or dialogs)

Transition from KWWidgets state machines to Qt state machines

• Core functionality in KWWidgets state machines and equivalent (if available) in Qt (In Progress):

KWWidgets functionality	Present in Qt?
States have enter/leave events	yes
Transitions have start/stop events	only one event per transition ("triggered")
Ordering of state and transition events: transition - start origin state - leave destination state - enter transition - end	... different: origin state - exit transition - triggered destination state - enter
Clusters of states	yes - use hierarchy of states
Can save history of encountered steps and/or transitions	???
Can define custom inputs	???

• If some of these components are not available in Qt's state machine framework, it means some more refactoring/restructuring work

Transition from KWWidgets workflow manager to a workflow manager using Qt's state machines

• Will likely need to reimplement the four KWWidget workflow manager classes:
  • vtkKWWizardStep: a wizard step
  • vtkKWWizardWorkflow : a wizard workflow
  • vtkKWWizardWidget : a wizard widget, embedding UI (buttons) and a wizard workflow engine
  • vtkKWWizardDialog : a wizard dialog, embedding a wizard widget in a toplevel/dialog window.

Important classes

• ctkWorkflowStep - defines a step, in terms of both the widgets shown and the criteria for successful transition to the next step
• ctkWorkflow - manages transitions between steps
• ctkWorkflowWidget - provides a clientArea onto which a step's widgets should be placed
  • ctkWorkflowWidget - clientArea is a QWidget
  • ctkWorkflowStackedWidget - client area is a QStackedWidget
  • ctkWorkflowTabWidget - client area is a QTabWidget

To create a new workflow step

• derive ctkWorkflowStep
• implement validate(): evaluates user input and returns true if valid, false if not
• implement showUserInterface(): shows or enables the widgets associated with each step
• implement hideUserInterface(): hides or disables the widgets associated with each step

Overview of ctkWorkflow

<graphviz>

digraph workflow { subgraph cluster_0 { style=filled; color=lightgrey; node [style=filled,color=white]; "Processing 1" -> "Validation 1" [label="validationTransition"];

               "Validation 1" -> "Processing 1" [label="validationFailedTransition"];

label = "ctkWorkflowStep* step1"; }

subgraph cluster_1 {

               style=filled;

color=lightgrey; node [style=filled,color=white]; "Processing 2" -> "Validation 2" [label="validationTransition"];

               "Validation 2" -> "Processing 2" [label="validationFailedTransition"];

label = "ctkWorkflowStep* step2"; }

       "Validation 1" -> "Processing 2" [label="validationSucceededTransition"];
       "Processing 2" -> "Processing 1" [label="goBackToSelfTransition"];

} </graphviz>

Signal/slot mechanism to transition to the next step

• ex. user enters parameter values, and then clicks "Next" to go to the next step

<graphviz> digraph signalsAndSlotsNext {

       "SIGNAL: pushButton->clicked()" -> "SLOT: workflow->triggerValidationTransition()"
       "SLOT: workflow->triggerValidationTransition()" -> "posts ValidationTransition event" -> "SIGNAL: validationState->onEntry()" -> "SLOT: workflow->attemptToGoToNextStep()" -> "step1->validate()"

"step1->validate()" -> "posts ValidationSucceededTransition event" [label="true"]

       "posts ValidationSucceededTransition event" -> "SIGNAL: validationSucceededTransition->triggered()" -> "SLOT: workflow->showAndHideUserInterface()"
       "step1->validate()" -> "posts ValidationFailedTransition event" [label="false"]

       "SLOT: workflow->showAndHideUserInterface()" -> "step1->hideUserInterface()"
       "SLOT: workflow->showAndHideUserInterface()" -> "step2->showUserInterface()"

} </graphviz>

Signal/slot mechanism to trigger transition to the previous step

• ex. user clicks "Back" to go to the previous step

<graphviz> digraph signalsAndSlotsBack {

       "SIGNAL: pushButton->clicked()" -> "SLOT: workflow->triggerGoBackToSelfTransition()"
       "SLOT: workflow->triggerGoBackToSelfTransition()" -> "posts GoBackToSelfTransition event" -> "SIGNAL: goBackToSelfTransition->triggered()" -> "SLOT: workflow->showAndHideUserInterface()"
       "SLOT: workflow->showAndHideUserInterface()" -> "step2->hideUserInterface()"
       "SLOT: workflow->showAndHideUserInterface()" -> "step1->showUserInterface()

} </graphviz>

GUI implementation in Qt

• qStackedWidget (and/or qTabWidget)
• simply connect signal to the stacked widget's setCurrentIndex(int) slot to change the displayed widget
• plus qDialog as well
• in Qt Designer - could have one .ui file for the entire stacked widget, or, for widgets representing complicated steps, could have a separate .ui

Concepts to keep in mind

• Undo / redo and forward/back transitions
• Branching workflows / skipped states ("GoToSelf" in KWWidgets)
• Design / output of state machines in a graphical format
• Logging state transitions, user actions, inputs and results thoughout (logging states?)

Additional ideas and questions

• Image processing throughout - need to deal with failures in image processing that are unrelated to the GUI
• Would be a good idea to make the workflow manager as general as possible for CTK - ex. use for management of IGT workflows in Slicer, where you may be coordinating several modules (ex. calibration module -> registration module -> tracking module), and may need to notify other components of current state (ex. over OpenIGTLink) (ex see this IJ paper)
  • Ex. make a workflow step more generic: instead of an "interaction" state and a "validation" state, could think about a "do stuff" state and a "validation" state, where "do stuff" can be user interaction, image processing, etc.
  • In validation states, could also have "borderline" success, where you may want to warn the user and allow them to choose whether to go ahead to the next step or to redo the current step with different inputs
• May even like to provide the option to save the MRML tree at the end of each step (to restore state if there is a crash, for example