Event System (EventBus)

Overview

The EventBus is FreeWorld OS's central event system, similar to OS message queues. It enables completely decoupled communication between components, allowing them to work together without direct dependencies.

Key Features

• Decoupled Communication: Components communicate via events, not direct calls
• Event Types: Structured event types (e.g., input.mousedown, drag.start)
• Priority System: Events can have priorities for ordered processing
• Async Processing: Events are queued and processed asynchronously
• Event Cancellation: Events can be cancelled or propagation stopped
• Global Listeners: Listen to all events for debugging/monitoring

Event Types

Input Events

• input.mousedown - Mouse button pressed
• input.mouseup - Mouse button released
• input.mousemove - Mouse moved
• input.click - Mouse clicked
• input.dblclick - Mouse double-clicked
• input.contextmenu - Right-click context menu
• input.keydown - Key pressed
• input.keyup - Key released

Drag & Drop Events

• drag.start - Drag operation started
• drag.begin - Drag threshold crossed (actual drag)
• drag.move - Element being dragged
• drag.enter - Entered drop target
• drag.leave - Left drop target
• drag.drop - Dropped on target
• drag.end - Drag operation ended

Window Events

• window.create - Window created
• window.close - Window closed
• window.focus - Window focused
• window.blur - Window lost focus

Usage

Initialization

const eventBus = new EventBus();
window.freeworldEventBus = eventBus; // Make globally available

Subscribing to Events

// Subscribe to an event type
const unsubscribe = eventBus.on('input.mousedown', (event) => {
    console.log('Mouse down at:', event.data.x, event.data.y);
});

// Subscribe with options
eventBus.on('drag.start', (event) => {
    // Handle drag start
}, {
    priority: 10,  // Higher priority = processed first
    once: false    // Remove after first call
});

// Unsubscribe
unsubscribe();

Emitting Events

// Emit an event
eventBus.emit('input.mousedown', {
    x: 100,
    y: 200,
    button: 'left',
    target: element
}, {
    source: 'InputManager',
    cancelable: true
});

Global Listeners

// Listen to all events (for debugging)
eventBus.onAll((event) => {
    console.log('Event:', event.type, event.data);
});

Integration with Components

InputManager

The InputManager captures all mouse/keyboard input and emits standardized events to the EventBus.

DragDropSystem

The DragDropSystem subscribes to input events and emits drag/drop events, completely decoupled from other components.

GUI Server

The GUI server subscribes to events it needs (drag events, context menu events) and responds accordingly.

Benefits

• Modularity: Components can be added/removed without breaking others
• Testability: Components can be tested in isolation
• Debugging: All events flow through one system, easy to monitor
• Extensibility: New components can subscribe to existing events
• OS-like Architecture: Similar to how real OSes handle messages/events