Input System

Source: client/engine/systems/systems_functions/InputSystem.cpp

Purpose: Read logical action state from the InputManager and populate the Inputs component for player-controlled entities.

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Overview

The Input System bridges the gap between the Input Abstraction Layer and the ECS. It queries the InputManager for action states and updates Inputs components accordingly.

This system uses logical actions (e.g., MoveLeft, Shoot) instead of physical keys, making the game code independent of the underlying input backend (SFML, SDL, etc.).

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Components Used

Component	Access	Description
Inputs	Write	Stores movement direction and shoot state

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Dependencies

Dependency	Type	Description
InputManager<Game::Action>	Reference	Provides action state queries

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Behavior

1. Focus Check: Returns immediately if the window doesn't have focus
2. Action Queries: For each entity with Inputs:
   • Uses GetAxis() for smooth movement values (-1.0 to +1.0)
   • Uses IsActionActive() for discrete actions (shoot)
3. State Tracking: Preserves last_shoot_state for edge detection

Action to Input Mapping

Component Field	Negative Action	Positive Action
horizontal	MoveLeft	MoveRight
vertical	MoveUp	MoveDown
shoot	-	Shoot

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Function Signature

void InputSystem(
    Engine::registry &reg,
    Engine::Input::InputManager<Game::Action> &input_manager,
    Engine::sparse_array<Component::Inputs> &inputs);

Parameters

Parameter	Description
reg	Engine registry (unused but required for system signature)
input_manager	The input manager configured with game bindings
inputs	Sparse array of Inputs components to update

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Implementation

void InputSystem(Engine::registry &reg,
    Engine::Input::InputManager<Game::Action> &input_manager,
    Engine::sparse_array<Component::Inputs> &inputs) {
    
    // Ignore input when window loses focus
    if (!input_manager.HasFocus())
        return;

    for (auto &&[i, input] : make_indexed_zipper(inputs)) {
        // Track previous shoot state for edge detection
        input.last_shoot_state = input.shoot;

        // Use logical actions via GetAxis helper
        // Returns -1.0, 0.0, or +1.0 based on action state
        input.horizontal = input_manager.GetAxis(
            Game::Action::MoveLeft, 
            Game::Action::MoveRight);
        
        input.vertical = input_manager.GetAxis(
            Game::Action::MoveUp, 
            Game::Action::MoveDown);

        // Discrete action for shooting
        input.shoot = input_manager.IsActionActive(Game::Action::Shoot);
    }
}

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Default Key Bindings

The InputManager is configured with these default bindings (set in GameInputBindings.hpp):

Movement

Action	Primary	Secondary	Tertiary
MoveUp	Z	W	↑ Arrow
MoveDown	S	-	↓ Arrow
MoveLeft	Q	A	← Arrow
MoveRight	D	-	→ Arrow

Combat

Action	Primary	Secondary
Shoot	Space	Left Mouse Button

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Network Integration

The Inputs component is converted to a bitfield for network transmission:

uint8_t InputToBitfield(const Component::Inputs &input) {
    uint8_t bitfield = 0;

    if (input.vertical < 0.0f)   bitfield |= (1 << 0);  // Up
    if (input.vertical > 0.0f)   bitfield |= (1 << 1);  // Down
    if (input.horizontal < 0.0f) bitfield |= (1 << 2);  // Left
    if (input.horizontal > 0.0f) bitfield |= (1 << 3);  // Right
    if (input.shoot)             bitfield |= (1 << 4);  // Shoot

    return bitfield;
}

This follows the RFC Section 6.1 (PLAYER_INPUT) specification.

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Notes

• No Physical Keys: This system never checks sf::Keyboard directly
• Focus Handling: Prevents unintended input when alt-tabbed
• Backend Agnostic: Works with any IInputBackend implementation
• Key Remapping: Change bindings at runtime via InputManager::BindKey()

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Related Documentation

• Input Abstraction Layer - Full architecture documentation
• Button Click System - UI input handling
• Protocol RFC - Network input packet format