# Pong

Complete two-player game in ~150 lines.

```{raw} html
<a class="example-run-button" href="../demos/demos_pong.html">▶ Run in browser</a>

```

**Tags:** `game` `input-actions` `signals` `collision`

A classic Pong demonstrating input actions, signals, collision detection,
and game-state management. Player 1 uses W/S, player 2 uses Up/Down arrows.


## What you will learn

- **Input actions**: Bind keys to named actions with `InputMap.add_action()`.
- **Input.get_strength()**: Read analogue input strength for smooth movement.
- **Signals**: Decouple game events (the ball emits `scored` when it passes a paddle).
- **Collision**: Manual AABB overlap for paddle-ball bouncing.
- **Game state**: Track and display scores.

## How it works

Three node types compose the game:

- `Paddle` reads two input actions (up/down) and clamps position to the screen.
- `Ball` moves at a velocity, bounces off top/bottom edges, and emits a
  `scored` signal when it exits left or right.
- `PongGame` (root) declares `input_actions = {...}` at class scope, creates
  paddles and ball in `on_ready()`, connects the `scored` signal to update
  the score, and handles paddle-ball collision in `on_process()` by
  reflecting the ball's velocity based on where it hits the paddle.

The `input_actions` class attribute is the canonical registration path: the
scene tree consumes it at mount and re-applies on every `change_scene` swap.
It also works correctly under the web exporter, which instantiates the root
class directly without invoking `main()`.

## Source

```{literalinclude} ../../examples/demos/pong.py
:language: python
:linenos:
```