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  3. UInputBehavior

UInputBehavior

An InputBehavior implements a state machine for a user interaction.

API > API/Runtime > API/Runtime/InteractiveToolsFramework

Inheritance Hierarchy

References

   
Module InteractiveToolsFramework
Header /Engine/Source/Runtime/InteractiveToolsFramework/Public/InputBehavior.h
Include #include "InputBehavior.h"

Syntax

class UInputBehavior : public UObject

Remarks

An InputBehavior implements a state machine for a user interaction. The InputRouter maintains a set of active Behaviors, and when new input events occur, it calls WantsCapture() to check if the Behavior would like to begin capturing the applicable input event stream (eg for a mouse, one or both VR controllers, etc). If the Behavior acquires capture, UpdateCapture() is called until the Behavior indicates that it wants to release the device, or until the InputRouter force-terminates the capture via ForceEndCapture().

For example, something like ButtonSetClickBehavior might work as follows:

  • in WantsCapture(), if left mouse is pressed and a button is under cursor, return Begin, otherwise Ignore
  • in BeginCapture(), save identifier for button that is under cursor
  • in UpdateCapture()
  • if left mouse is down, return Continue
  • if left mouse is released:
  • if saved button is still under cursor, call button.Clicked()
  • return End

Written sufficiently generically, the above Behavior doesn't need to know about buttons, it just needs to know how to hit-test the clickable object(s). Similarly separate Behaviors can be written for mouse, VR, touch, gamepad, etc.

Implementing interactions in this way allows the input handling to be separated from functionality.

Variables

  Type Name Description
Protected variable FInputCapturePriority DefaultPriority Priority returned by GetPriority()

Constructors

  Type Name Description
Public function    

Functions

  Type Name Description
Public function Virtual FInputCaptureUpdate

BeginCapture ( const FInputDeviceState& InputState,
EInputCaptureSide eSide
)

 Called after WantsCapture() returns a capture request that was accepted
Public function Virtual FInputCaptureUpdate

BeginHoverCapture ( const FInputDeviceState& InputState,
EInputCaptureSide eSide
)

 Called after WantsHoverCapture() returns a capture request that was accepted
Public function Virtual void If a different hover capture begins, focus is lost, a tool starts, etc, any active hover visualization needs to terminate
Public function Virtual void

ForceEndCapture ( const FInputCaptureData& CaptureData
)

 If this is called, the Behavior has forcibly lost capture (eg due to app losing focus for example) and needs to clean up accordingly
Public function Virtual FInputCapturePriority The priority is used to resolve situations where multiple behaviors want the same capture
Public function Virtual EInputDevices Which device types does this Behavior support
Public function Virtual void Configure the default priority of an instance of this behavior
Public function Virtual FInputCaptureUpdate

UpdateCapture ( const FInputDeviceState& InputState,
const FInputCaptureData& CaptureData
)

 Called for each new input event during a capture sequence.
Public function Virtual FInputCaptureUpdate

UpdateHoverCapture ( const FInputDeviceState& InputState
)

 Called on each new hover input event, ie if no other behavior is actively capturing input
Public function Virtual FInputCaptureRequest

WantsCapture ( const FInputDeviceState& InputState
)

 Given the input state, does this Behavior want to begin capturing some input devices?
Public function Virtual FInputCaptureRequest

WantsHoverCapture ( const FInputDeviceState& InputState
)

 Given the input state, does this Behavior want to begin capturing some input devices for hover
Public function Virtual bool Hover support (optional)return true if this Behavior supports hover (ie passive input events)

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