Introduction
Prerequisites
Setting Up the Project
Implementation
Testing and Debugging
Conclusion

In this tutorial, we will build a basic real-time physics engine using C++. This engine will handle rigid body dynamics, collision detection, and real-time updates. By the end, you’ll have a simple but functional physics engine ready for further development.

Introduction

A physics engine simulates real-world physics for objects in a game or simulation. It involves understanding forces, motion, and collisions. This guide will cover setting up a simple engine with basic functionality.

Prerequisites

Ensure you have:

Basic knowledge of C++ programming
Understanding of fundamental physics concepts (e.g., Newton's Laws, forces)
A C++ development environment (e.g., Visual Studio, CLion)

Setting Up the Project

Create a New Project: Set up a new C++ project in your IDE.
Add Necessary Libraries: You might need libraries for math operations, such as GLM for vector mathematics.

Implementation

Vector2 Class

The Vector2 class represents 2D vectors and includes basic operations.

// Vector2.h
#ifndef VECTOR2_H
#define VECTOR2_H
 
class Vector2 {
public:
    float x, y;
 
    Vector2(float x = 0.0f, float y = 0.0f) : x(x), y(y) {}
 
    Vector2 operator+(const Vector2& v) const {
        return Vector2(x + v.x, y + v.y);
    }
 
    Vector2 operator-(const Vector2& v) const {
        return Vector2(x - v.x, y - v.y);
    }
 
    Vector2 operator*(float scalar) const {
        return Vector2(x * scalar, y * scalar);
    }
 
    Vector2& operator+=(const Vector2& v) {
        x += v.x;
        y += v.y;
        return *this;
    }
 
    float length() const {
        return sqrt(x * x + y * y);
    }
};
 
#endif // VECTOR2_H

RigidBody Class

The RigidBody class represents an object in the simulation, including its position, velocity, and mass.

// RigidBody.h
#ifndef RIGIDBODY_H
#define RIGIDBODY_H
 
#include "Vector2.h"
 
class RigidBody {
public:
    Vector2 position;
    Vector2 velocity;
    float mass;
 
    RigidBody(Vector2 pos = Vector2(), Vector2 vel = Vector2(), float m = 1.0f) 
        : position(pos), velocity(vel), mass(m) {}
 
    void applyForce(const Vector2& force, float deltaTime) {
        Vector2 acceleration = force * (1.0f / mass);
        velocity += acceleration * deltaTime;
    }
 
    void update(float deltaTime) {
        position += velocity * deltaTime;
    }
};
 
#endif // RIGIDBODY_H

PhysicsEngine Class

The PhysicsEngine class manages the simulation, updating all RigidBody instances.

// PhysicsEngine.h
#ifndef PHYSICSENGINE_H
#define PHYSICSENGINE_H
 
#include <vector>
#include "RigidBody.h"
 
class PhysicsEngine {
private:
    std::vector<RigidBody*> bodies;
 
public:
    void addBody(RigidBody* body) {
        bodies.push_back(body);
    }
 
    void update(float deltaTime) {
        for (auto& body : bodies) {
            body->update(deltaTime);
        }
    }
};
 
#endif // PHYSICSENGINE_H

Collision Detection

For simplicity, we'll use a basic collision detection mechanism that checks if two circles overlap.

// CollisionDetection.h
#ifndef COLLISIONDETECTION_H
#define COLLISIONDETECTION_H
 
#include "RigidBody.h"
#include <cmath>
 
bool checkCollision(const RigidBody& a, const RigidBody& b, float radius) {
    Vector2 distance = a.position - b.position;
    return distance.length() < (2 * radius);
}
 
#endif // COLLISIONDETECTION_H

Main Function

Combine everything in the main function to set up and run the simulation.

// main.cpp
#include <iostream>
#include "PhysicsEngine.h"
#include "RigidBody.h"
#include "CollisionDetection.h"
 
int main() {
    PhysicsEngine engine;
 
    RigidBody body1(Vector2(0.0f, 0.0f), Vector2(1.0f, 1.0f), 1.0f);
    RigidBody body2(Vector2(10.0f, 10.0f), Vector2(-1.0f, -1.0f), 1.0f);
 
    engine.addBody(&body1);
    engine.addBody(&body2);
 
    const float deltaTime = 0.016f; // 60 FPS
 
    for (int i = 0; i < 100; ++i) {
        engine.update(deltaTime);
 
        if (checkCollision(body1, body2, 1.0f)) {
            std::cout << "Collision detected!\n";
        }
    }
 
    return 0;
}

Testing and Debugging

Test the engine by running the simulation and observing the output. Use logging or visualization tools to check if the objects interact as expected.

Conclusion

In this tutorial, we created a basic real-time physics engine in C++. We implemented key components such as vector operations, rigid body dynamics, and collision detection. This foundation can be expanded with more advanced features and optimizations.

Feel free to experiment with the code and add new functionalities to fit your needs. Happy coding!

Creating a Real-Time Physics Engine with C++

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