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Snake Game Core Components

Introducing the foundational components for our game and setting up the project

Ryan McCombe
Updated

In this series, we'll build a fully functional Snake game from scratch, combining all the concepts we've covered so far.

As with our previous project, we'll separate our code into two main parts:

  1. An "Engine" module containing components that are generally useful across a wide range of projects, not specific to Snake.
  2. A Snake-specific module that builds upon our engine to create the actual game.

For example, we'll create a general Button class in our engine that can be used across various projects. The cells of our Snake grid will then inherit from this Button class, expanding it with Snake-specific logic.

The Globals.h File

Similar to our previous project, we'll create a header file to store configuration options for our game. This will include things like sizes, positions, colors, and the fonts and images we want to use.

We'll also include a helper function that checks and logs out if there are any SDL errors, as well as a CHECK_ERRORS preprocessor definition which we can turn off to disable this behavior.

src/Globals.h

#pragma once
#define CHECK_ERRORS

#include <iostream>
#include <SDL3/SDL.h>
#include <string>

namespace Config {
  // Game Settings
  inline const std::string GAME_NAME{"Snake"};
  inline constexpr int WINDOW_HEIGHT{400};
  inline constexpr int WINDOW_WIDTH{800};

  // Colors
  inline constexpr SDL_Color BACKGROUND_COLOR{
    85, 138, 52, 255};
  inline constexpr SDL_Color FONT_COLOR{
    255, 255, 255, 255};

  // Asset Paths
  inline const std::string BASE_PATH{
    SDL_GetBasePath()};
  inline const std::string APPLE_IMAGE{
    BASE_PATH + "apple.png"};
  inline const std::string FONT{
    BASE_PATH + "Rubik-SemiBold.ttf"};
}

inline void CheckSDLError(const std::string& Msg) {
#ifdef CHECK_ERRORS
  const char* error = SDL_GetError();
  if (*error != '\0') {
    std::cerr << Msg << " Error: "
      << error << '\n';
    SDL_ClearError();
  }
#endif
}

The Engine/Window.h File

Within the Engine directory, we'll include some generic helpers that our game can use. First, we'll have a Window class which we'll use to create and manage our SDL_Window:

src/Engine/Window.h

#pragma once
#include <SDL3/SDL.h>
#include "Globals.h"

namespace Engine {
class Window {
 public:
  Window() {
    SDLWindow = SDL_CreateWindow(
      Config::GAME_NAME.c_str(),
      Config::WINDOW_WIDTH,
      Config::WINDOW_HEIGHT,
      0
    );
    CheckSDLError("Creating Window");
  }

  ~Window() {
    if (SDLWindow && SDL_WasInit(SDL_INIT_VIDEO)) {
      SDL_DestroyWindow(SDLWindow);
    }
  }

  Window(const Window&) = delete;
  Window& operator=(const Window&) = delete;

  void Render() {
    const auto* Fmt = SDL_GetPixelFormatDetails(
      GetSurface()->format);
    SDL_FillSurfaceRect(
      GetSurface(), nullptr,
      SDL_MapRGB(
        Fmt, nullptr,
        Config::BACKGROUND_COLOR.r,
        Config::BACKGROUND_COLOR.g,
        Config::BACKGROUND_COLOR.b)
    );
  }

  void Update() {
    SDL_UpdateWindowSurface(SDLWindow);
  }

  SDL_Surface* GetSurface() {
    return SDL_GetWindowSurface(SDLWindow);
  }

 private:
  SDL_Window* SDLWindow{nullptr};
};
}

This Window class is similar to what we created in our earlier lesson on .

The Engine/Random.h File

Our game needs the ability to place apples in random cells. To support this, we'll include a Random namespace which includes the ability to generate random integers within a range defined by Min and Max arguments:

src/Engine/Random.h

#pragma once
#include <random>

namespace Engine::Random {
  inline std::random_device SEEDER;
  inline std::mt19937 ENGINE{SEEDER()};

  inline int Int(int Min, int Max) {
    std::uniform_int_distribution Get{Min, Max};
    return Get(ENGINE);
  }
}

This file uses techniques we covered in our introductory lesson on .

The Engine/Text.h File

We'll include a Text class that uses SDL3_ttf to load a font and render text onto an SDL_Surface:

src/Engine/Text.h

#pragma once
#include <SDL3/SDL.h>
#include <SDL3_ttf/SDL_ttf.h>
#include <string>
#include "Globals.h"

namespace Engine {
class Text {
 public:
  Text(const std::string& InitialText, int FontSize)
    : Content(InitialText),
      Font(nullptr),
      TextSurface(nullptr)
  {
    Font = TTF_OpenFont(
      Config::FONT.c_str(), (float)FontSize
    );
    CheckSDLError("Opening Font");
    SetText(InitialText);
  }

  ~Text() {
    if (TextSurface) {
      SDL_DestroySurface(TextSurface);
    }
    if (TTF_WasInit() && Font) {
      TTF_CloseFont(Font);
    }
  }

  Text(const Text&) = delete;
  Text& operator=(const Text&) = delete;

  void SetText(const std::string& NewText) {
    Content = NewText;

    if (TextSurface) {
      SDL_DestroySurface(TextSurface);
    }
    TextSurface = TTF_RenderText_Blended(
      Font, Content.c_str(), 0, Config::FONT_COLOR
    );
    CheckSDLError("Creating Text Surface");
  }

  void Render(SDL_Surface* Surface, SDL_Rect* Rect) {
    if (TextSurface) {
      SDL_BlitSurface(
        TextSurface, nullptr, Surface, Rect
      );
    }
  }

 private:
  std::string Content;
  TTF_Font* Font{nullptr};
  SDL_Surface* TextSurface{nullptr};
};
}

This Text class uses the techniques we covered in our introduction to .

The Engine/Image.h File

The last file in our Engine directory contains an Image class that uses SDL3_image to render an image onto an SDL_Surface:

src/Engine/Image.h

#pragma once
#include <SDL3/SDL.h>
#include <SDL3_image/SDL_image.h>
#include <string>
#include "Globals.h"

namespace Engine {
class Image {
 public:
  Image(const std::string& Path) {
    ImageSurface = IMG_Load(Path.c_str());
    CheckSDLError("Loading Image");
  }

  ~Image() {
    if (ImageSurface) {
      SDL_DestroySurface(ImageSurface);
    }
  }

  void Render(SDL_Surface* Surface, SDL_Rect* Rect) {
    SDL_BlitSurfaceScaled(
      ImageSurface, nullptr,
      Surface, Rect,
      SDL_SCALEMODE_LINEAR
    );
  }

  // Prevent copying
  Image(const Image&) = delete;
  Image& operator=(const Image&) = delete;

 private:
  SDL_Surface* ImageSurface{nullptr};
};
}

This Image class uses the techniques we covered in our introduction to images, surface blitting, and .

The Assets.h File

We'll create an asset manager class to make our shared assets available to any component that needs them. In this project, we'll only need to share our apple image, but we'll create an Assets class to take care of this and give us an easy way to expand our asset collection as needed:

src/Assets.h

#pragma once
#include "Globals.h"
#include "Engine/Image.h"

struct Assets {
  Engine::Image Apple{Config::APPLE_IMAGE};
};

The SnakeUI.h File

To manage our UI elements, we'll create a SnakeUI class. It includes our standard set of game loop methods, HandleEvent(), Tick() and Render().

It will forward these calls to the UI elements it manages, once we create them.

src/SnakeUI.h

#pragma once
#include <SDL3/SDL.h>
#include "Assets.h"

class SnakeUI {
 public:
  void HandleEvent(const SDL_Event& E) {}
  void Tick(Uint64 DeltaTime) {}
  void Render(SDL_Surface* Surface) {}

 private:
  Assets AssetList;
};

The main.cpp File

Let's hook everything up in our main() function. It implements the standard game loop and event loop setup we've used throughout the course. We'll forward events, tick, and render our Window and SnakeUI as appropriate.

We'll also calculate the time delta between frames to help our Tick() functions. We'll provide these time deltas in milliseconds:

src/main.cpp

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>
#include <SDL3_image/SDL_image.h>
#include <SDL3_ttf/SDL_ttf.h>

#include "Globals.h"
#include "Engine/Window.h"
#include "SnakeUI.h"

int main(int, char**) {
  SDL_Init(SDL_INIT_VIDEO);
  CheckSDLError("Initializing SDL");

  TTF_Init();
  CheckSDLError("Initializing SDL_ttf");

  Engine::Window GameWindow{};
  SnakeUI UI{};

  Uint64 PreviousTick{SDL_GetTicks()};
  Uint64 CurrentTick;
  Uint64 DeltaTime;

  SDL_Event Event;
  bool IsRunning = true;
  while (IsRunning) {
    CurrentTick = SDL_GetTicks();
    DeltaTime = CurrentTick - PreviousTick;

    // Events
    while (SDL_PollEvent(&Event)) {
      UI.HandleEvent(Event);
      if (Event.type == SDL_EVENT_QUIT) {
        IsRunning = false;
      }
    }

    // Tick
    UI.Tick(DeltaTime);

    // Render
    GameWindow.Render();
    UI.Render(GameWindow.GetSurface());

    // Swap
    GameWindow.Update();

    PreviousTick = CurrentTick;
  }

  TTF_Quit();
  SDL_Quit();
  return 0;
}

Assets and Dependencies

This project requires a font to render text, and an image to represent the apples that our snake eats. Our implementation assumes that the apple image is an approximately square .png file with a transparent background. The screenshot and code examples in this chapter are using the following assets:

As before, we'll store our font and image in the same directory as our program executable to ensure SDL_ttf and SDL_image can find them at run time.

The CMakeLists.txt File

Those using the CMake build automation tool may find the following CMakeLists.txt file helpful. It assumes we're building the SDL libraries (SDL3, SDL3_image, and SDL3_ttf) from a subdirectory called /vendor, consistent with our earlier setup lessons:

CMakeLists.txt

cmake_minimum_required(VERSION 3.23)

project(
  Minesweeper
  VERSION 1.0
  DESCRIPTION "Snake"
  LANGUAGES CXX
)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(
  CMAKE_RUNTIME_OUTPUT_DIRECTORY
  "${CMAKE_BINARY_DIR}/$<CONFIGURATION>"
)

set(
  CMAKE_LIBRARY_OUTPUT_DIRECTORY
  "${CMAKE_BINARY_DIR}/$<CONFIGURATION>"
)

add_executable(Snake
  src/main.cpp
  
  # This will be added later
  # src/Snake/Cell.cpp
)

target_include_directories(Snake
  PRIVATE ${PROJECT_SOURCE_DIR}/src
)

if(APPLE)
  set_target_properties(Snake PROPERTIES
    INSTALL_RPATH "@executable_path;@loader_path"
    BUILD_WITH_INSTALL_RPATH TRUE
    MACOSX_RPATH TRUE
  )
elseif(UNIX)
  set_target_properties(Snake PROPERTIES
    INSTALL_RPATH "$ORIGIN"
    BUILD_WITH_INSTALL_RPATH TRUE
  )
endif()

set(SDLTTF_VENDORED ON)
set(VENDOR_DIR "${PROJECT_SOURCE_DIR}/vendor")
add_subdirectory(${VENDOR_DIR}/SDL)
add_subdirectory(${VENDOR_DIR}/SDL_image)
add_subdirectory(${VENDOR_DIR}/SDL_ttf)

target_link_libraries(Snake
  SDL3::SDL3
  SDL3_image::SDL3_image
  SDL3_ttf::SDL3_ttf
)

We covered this approach to setting up an SDL project in a dedicated chapter .

Running the Project

Our project should compile and run successfully. We should see a window with the title, width, height, and background color we defined in Globals.h:

Summary

This lesson covered the essential building blocks of our Snake game, implementing the core game loop and supporting features. Key components:

  • The Globals.h header file stores configuration variables that will control our game's logic and presentation.
  • The Engine::Window class is responsible for managing our window, including the underlying SDL_Window pointer.
  • The Engine::Random namespace allows us to generate random integers, which we'll need to dynamically position the apples our snake needs to eat.
  • The Engine::Text and Engine::Image classes manage the rendering of fonts and image files, providing the content in the form of an SDL_Surface.
  • The Assets class manages our image assets, allowing them to be shared across multiple components later in our game.
  • The SnakeUI class is where we will construct and orchestrate all of our UI elements as we build them in future lessons.
  • The main function in main.cpp pulls everything together by initializing the core components and implementing a standard application loop to manage our systems.
Next Lesson
Lesson 59 of 61

Building the Snake Grid

Build the foundational grid structure that will power our Snake game's movement and collision systems.

Continue to Next Lesson
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