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Building a Game Engine

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Introduction

Building a game engine is a complex but rewarding task that involves integrating various components such as rendering, physics, input handling, and more. In this section, we will guide you through the fundamental steps required to create a basic game engine using DirectX. By the end of this module, you will have a solid understanding of how to structure a game engine and implement essential features.

Key Concepts

  1. Game Loop: The core loop that drives the game, handling updates and rendering.
  2. Subsystems: Different components like rendering, physics, input, and audio.
  3. Entity-Component System (ECS): A design pattern for organizing game objects.
  4. Resource Management: Handling assets like textures, models, and shaders.
  5. Scene Management: Organizing and managing different scenes or levels in the game.

Step-by-Step Guide

  1. Setting Up the Game Loop

The game loop is the heart of any game engine. It continuously updates the game state and renders the scene.

#include <windows.h>
#include <d3d11.h>
#include <chrono>

// Global Declarations
HWND hwnd;
ID3D11Device* device = nullptr;
ID3D11DeviceContext* context = nullptr;
IDXGISwapChain* swapChain = nullptr;
ID3D11RenderTargetView* renderTargetView = nullptr;

// Function Prototypes
void InitializeDirectX(HWND hwnd);
void Render();
void Update();
void Cleanup();

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
    switch (uMsg) {
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
        default:
            return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    // Window Initialization
    WNDCLASSEX wc = { sizeof(WNDCLASSEX), CS_CLASSDC, WindowProc, 0L, 0L, GetModuleHandle(NULL), NULL, NULL, NULL, NULL, _T("DirectXWindow"), NULL };
    RegisterClassEx(&wc);
    hwnd = CreateWindow(wc.lpszClassName, _T("DirectX Game Engine"), WS_OVERLAPPEDWINDOW, 100, 100, 800, 600, NULL, NULL, wc.hInstance, NULL);
    ShowWindow(hwnd, nCmdShow);

    // DirectX Initialization
    InitializeDirectX(hwnd);

    // Game Loop
    MSG msg = { 0 };
    auto previousTime = std::chrono::high_resolution_clock::now();
    while (msg.message != WM_QUIT) {
        if (PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE)) {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        } else {
            auto currentTime = std::chrono::high_resolution_clock::now();
            std::chrono::duration<float> deltaTime = currentTime - previousTime;
            previousTime = currentTime;

            Update();
            Render();
        }
    }

    // Cleanup
    Cleanup();
    UnregisterClass(wc.lpszClassName, wc.hInstance);
    return 0;
}

void InitializeDirectX(HWND hwnd) {
    // DirectX Initialization Code
    // ...
}

void Render() {
    // Rendering Code
    // ...
}

void Update() {
    // Update Game State
    // ...
}

void Cleanup() {
    // Cleanup Code
    // ...
}

  1. Implementing Subsystems

Rendering Subsystem

The rendering subsystem is responsible for drawing objects on the screen.

void InitializeDirectX(HWND hwnd) {
    // Create Device and SwapChain
    DXGI_SWAP_CHAIN_DESC scd = {};
    scd.BufferCount = 1;
    scd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
    scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
    scd.OutputWindow = hwnd;
    scd.SampleDesc.Count = 4;
    scd.Windowed = TRUE;

    D3D11CreateDeviceAndSwapChain(NULL, D3D_DRIVER_TYPE_HARDWARE, NULL, 0, NULL, 0, D3D11_SDK_VERSION, &scd, &swapChain, &device, NULL, &context);

    // Create Render Target View
    ID3D11Texture2D* backBuffer;
    swapChain->GetBuffer(0, __uuidof(ID3D11Texture2D), (LPVOID*)&backBuffer);
    device->CreateRenderTargetView(backBuffer, NULL, &renderTargetView);
    backBuffer->Release();

    context->OMSetRenderTargets(1, &renderTargetView, NULL);

    // Set Viewport
    D3D11_VIEWPORT viewport = {};
    viewport.Width = 800;
    viewport.Height = 600;
    viewport.MinDepth = 0.0f;
    viewport.MaxDepth = 1.0f;
    context->RSSetViewports(1, &viewport);
}

void Render() {
    // Clear the back buffer
    float clearColor[4] = { 0.0f, 0.2f, 0.4f, 1.0f };
    context->ClearRenderTargetView(renderTargetView, clearColor);

    // Present the back buffer to the screen
    swapChain->Present(1, 0);
}

Input Handling Subsystem

The input handling subsystem captures and processes user inputs.

void Update() {
    // Example: Simple Input Handling
    if (GetAsyncKeyState(VK_ESCAPE)) {
        PostQuitMessage(0);
    }
}

  1. Entity-Component System (ECS)

An ECS is a design pattern that helps manage game objects in a flexible and efficient way.

Entity

An entity is a unique identifier for a game object.

struct Entity {
    int id;
};

Component

Components are data structures that hold the properties of entities.

struct TransformComponent {
    float x, y, z;
};

struct RenderComponent {
    // Rendering properties
};

System

Systems operate on entities with specific components.

class RenderSystem {
public:
    void Update(std::vector<Entity>& entities, std::vector<TransformComponent>& transforms, std::vector<RenderComponent>& renders) {
        for (size_t i = 0; i < entities.size(); ++i) {
            // Render logic
        }
    }
};

  1. Resource Management

Efficiently managing resources like textures, models, and shaders is crucial for performance.

class ResourceManager {
public:
    ID3D11ShaderResourceView* LoadTexture(const std::string& filename) {
        // Load texture from file
    }
};

  1. Scene Management

Organizing and managing different scenes or levels in the game.

class Scene {
public:
    void Load() {
        // Load scene resources
    }

    void Update() {
        // Update scene
    }

    void Render() {
        // Render scene
    }
};

Practical Exercise

Exercise: Create a Basic Game Engine Structure

  1. Objective: Implement a basic game engine structure with a game loop, rendering subsystem, and input handling.
  2. Steps:
    • Set up a window and initialize DirectX.
    • Implement a game loop that updates and renders the game.
    • Add a simple input handling mechanism to close the window when the ESC key is pressed.
    • Create a basic rendering subsystem that clears the screen with a color.

Solution

Refer to the code snippets provided in the step-by-step guide above.

Conclusion

In this section, we covered the fundamental steps required to build a basic game engine using DirectX. We discussed the importance of the game loop, subsystems, ECS, resource management, and scene management. By following the provided examples and exercises, you should now have a solid foundation to expand and enhance your game engine further. In the next module, we will delve into integrating physics into your game engine.

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