UInputBehavior

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.