1. Introduction

This tutorial aims to guide you through implementing game physics in 2D games. Physics can add a layer of realism and interactivity to your games, making them more engaging for players.

By the end of this tutorial, you will have learned:

• Basic concepts of game physics, such as gravity, friction, and collision detection.
• How to implement these concepts into your 2D games.

Please note, this tutorial assumes you have a basic understanding of programming languages, preferably JavaScript, and some familiarity with game development.

2. Step-by-Step Guide

Understanding Game Physics

Game physics refers to the simulation of the laws of physics in a game environment. This includes gravity, which pulls objects downwards; friction, which slows down moving objects; and collision detection, which determines when objects bump into each other.

Implementing Gravity

Gravity can be implemented by continuously applying a downward force to your game objects. In a 2D game, you can achieve this by steadily increasing your object's Y-coordinate.

Implementing Friction

Friction can be simulated by applying a force that opposes your object's direction of movement. This usually involves slightly reducing the object's speed over time.

Implementing Collision Detection

Collision detection involves determining whether two game objects are overlapping. There are several ways to do this, but a common method is to check if the bounding boxes of two objects intersect.

3. Code Examples

Implementing Gravity

Here's an example of how you could implement gravity in JavaScript:

class GameObject {
  // constructor
  constructor(x, y, speed) {
    this.x = x;
    this.y = y;
    this.speed = speed;
    this.gravity = 0.5;
    this.velocity = 0;
  }
  // method to update the object's position
  update() {
    this.velocity += this.gravity; // increase the vertical speed by the gravity value
    this.y += this.velocity; // increase the y-coordinate by the current vertical speed
  }
}

In the above code, we define a GameObject class with an update method. This method uses a gravity value to steadily increase the object's vertical speed (velocity), and then uses this speed to update the object's Y-coordinate.

Implementing Friction

Here's an example of how you could implement friction:

class GameObject {
  // constructor
  constructor(x, y, speed) {
    this.x = x;
    this.y = y;
    this.speed = speed;
    this.friction = 0.9;
  }
  // method to update the object's position
  update() {
    this.speed *= this.friction; // reduce the speed by the friction value
    this.x += this.speed; // increase the x-coordinate by the current speed
  }
}

In this code, the update method applies friction by multiplying the object's speed (speed) by a friction factor, which is less than 1. This reduces the object's speed over time. The object's X-coordinate is then updated based on its new speed.

Implementing Collision Detection

One way to implement collision detection is by checking for bounding box overlap:

function checkCollision(object1, object2) {
  // check for overlap
  if (object1.x < object2.x + object2.width &&
      object1.x + object1.width > object2.x &&
      object1.y < object2.y + object2.height &&
      object1.y + object1.height > object2.y) {
    return true;
  }
  return false;
}

In the above function checkCollision, we check whether two objects' bounding boxes overlap. If they do, the function returns true; otherwise, it returns false.

4. Summary

In this tutorial, we've covered the basics of how to implement game physics in 2D games. We've learned about gravity, friction, and collision detection, and how to code these concepts in JavaScript.

To further your understanding, consider exploring more complex physics concepts, like momentum and angular velocity. You can also check out game development libraries such as Phaser.js, which have built-in physics engines that can handle a lot of this for you.

5. Practice Exercises

1. Create a game object that falls to the bottom of the screen due to gravity.
2. Add friction to the game object so that it gradually slows down as it moves horizontally.
3. Implement collision detection so that the game object stops when it hits the bottom of the screen.

Solutions:

1. Gravity: This involves creating a GameObject instance and using a loop to continuously call its update method.
2. Friction: This involves modifying the GameObject class to include a friction attribute, and then applying this friction in the update method.
3. Collision Detection: This involves adding a checkCollision function and using it to stop the game object when it hits the bottom of the screen.

Remember, practice is key in mastering these concepts, so try to apply them in your own projects!