Your first game in C++

This is the shortest path from an empty main.cpp to something moving on screen. It takes about ten minutes and introduces the four pieces every game has: an application, a plugin, an entity, and a system.

1. The application

Create main.cpp:

#include "Core/Application.hpp"

int main() {
    Engine::ApplicationConfig config;
    config.windowTitle = "My First Game";
    config.windowWidth = 1280;
    config.windowHeight = 720;
    config.targetFPS = 60;

    Engine::Application app(config);
    app.Run();
    return 0;
}

Application owns the window, the registry, and the loop. Run() blocks until the window closes. At this point you have a black window: nothing is registered and nothing is drawn.

2. A plugin

Plugins register components, systems, and resources. Add the shape plugin so we can draw a rectangle without loading an asset:

#include "Plugins/ShapePlugin.hpp"

Engine::ShapePlugin shapes;
shapes.Init(app.GetRegistry());

ShapePlugin::Init() registers ShapeComponent and ShapeSystem, along with the Position component and the opacity component. Registration order inside the plugin is already correct.

3. An entity

Engine::Registry& registry = app.GetRegistry();
Engine::Entity player = registry.CreateEntity();

Engine::ShapeComponent body;
body.type = Engine::ShapeType::RECTANGLE;
body.width = 48.0f;
body.height = 32.0f;
body.color = SKYBLUE;

Engine::ShapePlugin::AttachToEntity(registry, player, body);
registry.RequireComponent<Engine::Position>(player) =
    Engine::Position(220.0f, 320.0f, 10);

CreateEntity() gives every entity a default Position and Rotation. RequireComponent<T>() returns a reference and throws ErrorEcs if the component is missing; GetComponent<T>() returns an std::optional when you want to check first.

Run it: a blue rectangle appears at (220, 320). It is drawn by ShapeSystem, which looks for entities with a Position and a ShapeComponent.

4. A system

Static rectangles are not a game. A system moves things:

#include "Components/Position.hpp"
#include "ECS/System.hpp"

class MoveSystem : public Engine::System {
  public:
    void Update(Engine::Registry& registry, float dt) override {
        for (auto& [entity, position] : *registry.GetComponentArray<Engine::Position>()) {
            position.x += 140.0f * dt;

            if (position.x > 1200.0f) {
                position.x = -48.0f; // wrap around
            }
        }
    }
};

Register it after the shape plugin:

registry.RegisterSystem<MoveSystem>();

Systems update in registration order, once per fixed step. dt is the step length in seconds, so the speed is the same at 30, 60, or 144 FPS.

5. The complete main.cpp

#include "Components/Position.hpp"
#include "Components/ShapeComponent.hpp"
#include "Core/Application.hpp"
#include "ECS/System.hpp"
#include "Plugins/ShapePlugin.hpp"

class MoveSystem : public Engine::System {
  public:
    void Update(Engine::Registry& registry, float dt) override {
        for (auto& [entity, position] : *registry.GetComponentArray<Engine::Position>()) {
            position.x += 140.0f * dt;
            if (position.x > 1200.0f) {
                position.x = -48.0f;
            }
        }
    }
};

int main() {
    Engine::ApplicationConfig config;
    config.windowTitle = "My First Game";
    config.windowWidth = 1280;
    config.windowHeight = 720;
    config.targetFPS = 60;

    Engine::Application app(config);
    Engine::Registry& registry = app.GetRegistry();

    Engine::ShapePlugin shapes;
    shapes.Init(registry);

    Engine::Entity player = registry.CreateEntity();

    Engine::ShapeComponent body;
    body.type = Engine::ShapeType::RECTANGLE;
    body.width = 48.0f;
    body.height = 32.0f;
    body.color = SKYBLUE;
    Engine::ShapePlugin::AttachToEntity(registry, player, body);
    registry.RequireComponent<Engine::Position>(player) =
        Engine::Position(220.0f, 320.0f, 10);

    registry.RegisterSystem<MoveSystem>();

    app.Run();
    return 0;
}

Build it as part of the project, or add it to Games/CMakeLists.txt, run it, and the rectangle crosses the window.

Where to go next

I want to…	Read
Understand the model	Core concepts and Registry
Add sprites and text	Rendering
React to the keyboard	Input
Play sounds	Audio
Detect hits and triggers	Collisions
Build and edit scenes visually	Interface