3b1b-manim/manim_docs/modules/event_handler.md

Event Handler Module README

Overview

The event handler module manages user interactions and events in Manim. It provides a system for handling keyboard and mouse events, allowing for interactive animations and user input.

Key Components

1. Event Dispatcher (event_dispatcher.py)

• Purpose: Central event management system
• Key Features:
  • Registers and manages event listeners
  • Dispatches events to appropriate handlers
  • Handles event propagation
• Usage:

  dispatcher = EventDispatcher()
  dispatcher.add_listener(event_type, handler)
  

2. Event Listener (event_listner.py)

• Purpose: Handles individual event subscriptions
• Key Features:
  • Manages event callbacks
  • Handles event priority
  • Controls event propagation
• Usage:

  listener = EventListener(handler, priority=0)
  

3. Event Types (event_type.py)

• Purpose: Defines different types of events
• Key Features:
  • Keyboard events
  • Mouse events
  • Custom event types
• Usage:

  class CustomEvent(EventType):
      pass
  

Event Types

1. Keyboard Events

• Key press events
• Key release events
• Special key combinations

2. Mouse Events

• Mouse movement
• Mouse clicks
• Mouse drag
• Mouse wheel

3. Custom Events

• Scene-specific events
• Animation events
• State change events

Interaction with Other Modules

1. Scene Module:

   • Scenes register event handlers
   • Events can trigger scene changes
   • Interactive scenes use event system

2. Animation Module:

   • Events can control animations
   • Animation state changes trigger events
   • Interactive animations use event system

3. Mobject Module:

   • Mobjects can respond to events
   • Events can modify mobject properties
   • Interactive mobjects use event system

Best Practices

1. Event Handling:

   • Keep handlers focused and simple
   • Use appropriate event priorities
   • Handle event propagation carefully

2. Performance:

   • Minimize event handler complexity
   • Use event filtering when possible
   • Consider event frequency

3. Code Organization:

   • Group related event handlers
   • Use event types appropriately
   • Document event dependencies

Example Usage

class InteractiveExample(Scene):
    def construct(self):
        # Create interactive mobject
        circle = Circle()
        self.add(circle)
        
        # Define event handlers
        def on_key_press(event):
            if event.key == "LEFT":
                circle.shift(LEFT)
            elif event.key == "RIGHT":
                circle.shift(RIGHT)
        
        # Register event handler
        self.add_key_press_handler(on_key_press)
        
        # Interactive loop
        self.wait()