Learn to Make an Alien Farm Game With C++ SDL2 From Scratch

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Creating a game from scratch is an exciting journey that involves multiple aspects of programming, from understanding the basics of a language to mastering game development libraries. In this tutorial, we will walk through the steps to create a simple "Alien Farm" game using C++ and the Simple DirectMedia Layer 2 (SDL2) library.

Prerequisites

Before we start, ensure you have the following installed on your system:

A C++ compiler (GCC, Clang, or MSVC)
SDL2 library
SDL2_image library (for handling images)
A text editor or an IDE like Visual Studio Code

Setting Up Your Development Environment

Install SDL2 and SDL2_image:
- On Windows, you can download the development libraries from the SDL website and follow the installation instructions.
- On macOS, you can use Homebrew:
```
sh
brew install sdl2 sdl2_image
```
- On Linux, you can install them using your package manager. For example, on Ubuntu:
```
sh
sudo apt-get install libsdl2-dev libsdl2-image-dev
```

Set Up Your Project Structure: Create a directory for your project and inside it, create the following structure:

css
AlienFarm/
├── src/
│   ├── main.cpp
├── assets/
│   ├── alien.png
│   ├── farm.png
└── Makefile

Writing the Game

Initialize SDL2:

In main.cpp, start by including the necessary headers and initializing SDL2.

cpp
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <iostream>

const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;

bool initSDL(SDL_Window** window, SDL_Renderer** renderer) {
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        std::cerr << "SDL could not initialize! SDL_Error: " << SDL_GetError() << std::endl;
        return false;
    }

    *window = SDL_CreateWindow("Alien Farm", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
    if (!*window) {
        std::cerr << "Window could not be created! SDL_Error: " << SDL_GetError() << std::endl;
        return false;
    }

    *renderer = SDL_CreateRenderer(*window, -1, SDL_RENDERER_ACCELERATED);
    if (!*renderer) {
        std::cerr << "Renderer could not be created! SDL_Error: " << SDL_GetError() << std::endl;
        return false;
    }

    int imgFlags = IMG_INIT_PNG;
    if (!(IMG_Init(imgFlags) & imgFlags)) {
        std::cerr << "SDL_image could not initialize! IMG_Error: " << IMG_GetError() << std::endl;
        return false;
    }

    return true;
}

void closeSDL(SDL_Window* window, SDL_Renderer* renderer) {
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    IMG_Quit();
    SDL_Quit();
}

int main(int argc, char* args[]) {
    SDL_Window* window = nullptr;
    SDL_Renderer* renderer = nullptr;

    if (!initSDL(&window, &renderer)) {
        std::cerr << "Failed to initialize!" << std::endl;
        return -1;
    }

    bool quit = false;
    SDL_Event e;

    while (!quit) {
        while (SDL_PollEvent(&e) != 0) {
            if (e.type == SDL_QUIT) {
                quit = true;
            }
        }

        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderClear(renderer);

        // Render game objects here

        SDL_RenderPresent(renderer);
    }

    closeSDL(window, renderer);
    return 0;
}

Loading and Rendering Images:

Next, load and render images. Add the following functions to main.cpp to load textures and render them.

cpp
SDL_Texture* loadTexture(const std::string &path, SDL_Renderer* renderer) {
    SDL_Texture* newTexture = nullptr;
    SDL_Surface* loadedSurface = IMG_Load(path.c_str());
    if (!loadedSurface) {
        std::cerr << "Unable to load image " << path << "! SDL_image Error: " << IMG_GetError() << std::endl;
        return nullptr;
    }
    newTexture = SDL_CreateTextureFromSurface(renderer, loadedSurface);
    if (!newTexture) {
        std::cerr << "Unable to create texture from " << path << "! SDL Error: " << SDL_GetError() << std::endl;
    }
    SDL_FreeSurface(loadedSurface);
    return newTexture;
}

void renderTexture(SDL_Texture* texture, SDL_Renderer* renderer, int x, int y) {
    SDL_Rect renderQuad = { x, y, 100, 100 }; // Adjust width and height as needed
    SDL_RenderCopy(renderer, texture, NULL, &renderQuad);
}

Load and render the alien and farm images in the main game loop.

cpp
int main(int argc, char* args[]) {
    SDL_Window* window = nullptr;
    SDL_Renderer* renderer = nullptr;

    if (!initSDL(&window, &renderer)) {
        std::cerr << "Failed to initialize!" << std::endl;
        return -1;
    }

    SDL_Texture* alienTexture = loadTexture("assets/alien.png", renderer);
    SDL_Texture* farmTexture = loadTexture("assets/farm.png", renderer);
    if (!alienTexture || !farmTexture) {
        std::cerr << "Failed to load textures!" << std::endl;
        return -1;
    }

    bool quit = false;
    SDL_Event e;

    while (!quit) {
        while (SDL_PollEvent(&e) != 0) {
            if (e.type == SDL_QUIT) {
                quit = true;
            }
        }

        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderClear(renderer);

        renderTexture(farmTexture, renderer, 0, 0); // Background
        renderTexture(alienTexture, renderer, 350, 250); // Alien

        SDL_RenderPresent(renderer);
    }

    SDL_DestroyTexture(alienTexture);
    SDL_DestroyTexture(farmTexture);
    closeSDL(window, renderer);
    return 0;
}

Handling User Input:

To make the game interactive, we need to handle user input. Modify the event loop to handle key presses.

cpp
int main(int argc, char* args[]) {
    SDL_Window* window = nullptr;
    SDL_Renderer* renderer = nullptr;

    if (!initSDL(&window, &renderer)) {
        std::cerr << "Failed to initialize!" << std::endl;
        return -1;
    }

    SDL_Texture* alienTexture = loadTexture("assets/alien.png", renderer);
    SDL_Texture* farmTexture = loadTexture("assets/farm.png", renderer);
    if (!alienTexture || !farmTexture) {
        std::cerr << "Failed to load textures!" << std::endl;
        return -1;
    }

    bool quit = false;
    SDL_Event e;

    int alienX = 350;
    int alienY = 250;

    while (!quit) {
        while (SDL_PollEvent(&e) != 0) {
            if (e.type == SDL_QUIT) {
                quit = true;
            } else if (e.type == SDL_KEYDOWN) {
                switch (e.key.keysym.sym) {
                    case SDLK_UP:
                        alienY -= 10;
                        break;
                    case SDLK_DOWN:
                        alienY += 10;
                        break;
                    case SDLK_LEFT:
                        alienX -= 10;
                        break;
                    case SDLK_RIGHT:
                        alienX += 10;
                        break;
                }
            }
        }

        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderClear(renderer);

        renderTexture(farmTexture, renderer, 0, 0); // Background
        renderTexture(alienTexture, renderer, alienX, alienY); // Alien

        SDL_RenderPresent(renderer);
    }

    SDL_DestroyTexture(alienTexture);
    SDL_DestroyTexture(farmTexture);
    closeSDL(window, renderer);
    return 0;
}

Adding Game Logic:

Finally, let's add some simple game logic. For example, you can add collision detection between the alien and certain objects on the farm.

cpp
bool checkCollision(SDL_Rect a, SDL_Rect b) {
    int leftA = a.x;
    int rightA = a.x + a.w;
    int topA = a.y;
    int bottomA = a.y + a.h;

    int leftB = b.x;
    int rightB = b.x + b.w;
    int topB = b.y;
    int bottomB = b.y + b.h;

    if (bottomA <= topB) {
        return false;
    }

    if (topA >= bottomB) {
        return false;

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Learn to Make an Alien Farm Game With C++ SDL2 From Scratch

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Prerequisites

Setting Up Your Development Environment

Writing the Game