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Input processing architecture diagram flow


Input Processing#


  • PlayerInput Uobject exists within PlayerController class that manages player input state

  • Handles mouse smoothing, custom debug , gesture recognition, etc

  • Spawned only on clients

  • Contains input *mappings* e.g. FInputActionKeyMapping & FInputAxisKeyMapping map friendly names to Keys e.g. 'W' to MoveForward

  • As an exception, contains debug function *bindings* that can be executed through console.

  • Bindings to actual functions (e.g. what happens when MoveForward is pressed) should be placed in UInputComponent

  • InputCoreTypes.cpp contains the hardware button definition mappings to keys


  • Contains all the input delegate *bindings* for an Actor

  • Links AxisMappings/ActionMappings to game actions/functions

Input Processing Loop:#

  1. FEngineLoop::Tick() process input
  • FPlatformMisc::PumpMessages() processes mouse & keyboard while SlateApp.PollGameDeviceState() process gamepad

  • The Windows MsgPump happens during the main engine loop (at least on Windows, controlled by GPumpingMessagesOutsideOfMainLoop)

  • Gamepad input always happens inside the main loop

  • Actual Input keys are recorded in a side band channel through WindowsMsgPmp->SceneViewport->GameViewport

  • Calls into PlayerController::InputKey() to give PlayerController a chance to add logic around input capture (e.g. execute custom debug binds)

    • We use PlayerController::InputKey() to execute our custom debug input binds before normal engine Input processing

    • PlayerInput::InputKey() - record the key events in PlayerInput::KeyStateMap. This is where you can add smoothing or custom input history

  • Input is polled in FEngineLoop.Tick() by calling which is before GEngine->Tick()

  1. World::Tick()=> Process Input & Fire Bindings on components (during PlayerController's tick group, default PrePhysics
  • PlayerController::TickActor() calls PlayerController::PlayerTick() only on local PlayerController that has PlayerInput object so not servers. Won't be called on servers for nonlocal PCs

  • PlayerController::PlayerTick()

  • PlayerController::TickPlayerInput()

  • PlayerInput::Tick()

  • PlayerController::ProcessPlayerInput

  • PlayerController::BuildInputStack() => Adds InputComponents in a stack that defines priority of what components get access to inputs first. Order from lowest priority to highest:

    • ControlledPawn (if input enabled)

    • any components inside ControlledPawn with InputComponent

    • LevelScriptActors with InputEnabled

    • PlayerController

    • All other Actors that have called Aactor::EnableInput(PlayerController) where PlayerController is this player controller

  • PlayerInput::ProcessInputStack() - Process the frame input's events with Input stack from BuildInputStack

    • virtual PlayerController::PreProcessInput() - can be overridden for work before firing input delegates

    • PlayerInput::ProcessInputStack() => Processes all the input delegate binds

    • virtual PlayerController::PostProcessInput() - can be overridden for work post firing input delegates

  1. Tick Player Controller Actor