Code Notes made by Vaibhav Rathod

SDL2 (Simple DirectMedia Layer)

4 min read

Written by Vaibhav Rathod

History

  • Who: Created by Sam Lantinga while working at Loki Software.
  • Why: To provide a cross-platform abstraction layer for graphics, audio, and input — enabling games to run on Windows, Linux, macOS, and consoles from a single codebase.
  • When: SDL 1.0 released in 1998. SDL2 (major rewrite) released in 2013. SDL3 released in 2024.

Introduction

What is SDL2?

  • A cross-platform multimedia library providing low-level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL/Direct3D.
  • Used by thousands of games and emulators. Powers many indie games on Steam.
  • Website: libsdl.org

Advantages

  • Cross-platform: Windows, Linux, macOS, iOS, Android, consoles.
  • Simple, C-based API — easy to use from C++.
  • Hardware-accelerated 2D rendering.
  • Excellent ecosystem: SDL_image, SDL_mixer, SDL_ttf, SDL_net.
  • Widely used — large community and documentation.

Disadvantages

  • 2D only in core SDL (need OpenGL/Vulkan for 3D).
  • C API — not object-oriented (wrap it yourself or use SDL2pp).
  • SDL3 is a breaking change from SDL2.

Installation & Setup

Linux (apt)

sudo apt install libsdl2-dev libsdl2-image-dev libsdl2-mixer-dev libsdl2-ttf-dev

macOS (Homebrew)

brew install sdl2 sdl2_image sdl2_mixer sdl2_ttf

Windows (vcpkg)

vcpkg install sdl2 sdl2-image sdl2-mixer sdl2-ttf

CMake

find_package(SDL2 REQUIRED)
target_link_libraries(MyGame SDL2::SDL2 SDL2::SDL2main)

Core Concepts

Initialization & Window

#include <SDL2/SDL.h>
 
int main(int argc, char* argv[]) {
    // Initialize SDL subsystems
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0) {
        SDL_Log("Init failed: %s", SDL_GetError());
        return 1;
    }
 
    // Create window
    SDL_Window* window = SDL_CreateWindow(
        "My Game",           // title
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        800, 600,            // width, height
        SDL_WINDOW_SHOWN     // flags
    );
 
    if (!window) {
        SDL_Log("Window failed: %s", SDL_GetError());
        SDL_Quit();
        return 1;
    }
 
    // ... game loop ...
 
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

Renderer & Drawing

// Create hardware-accelerated renderer
SDL_Renderer* renderer = SDL_CreateRenderer(
    window, -1,
    SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC
);
 
// Game loop
bool running = true;
SDL_Event event;
 
while (running) {
    // Handle events
    while (SDL_PollEvent(&event)) {
        if (event.type == SDL_QUIT) running = false;
    }
 
    // Clear screen (black)
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
    SDL_RenderClear(renderer);
 
    // Draw a red rectangle
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
    SDL_Rect rect = {100, 100, 200, 150};
    SDL_RenderFillRect(renderer, &rect);
 
    // Draw a blue line
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, 255);
    SDL_RenderDrawLine(renderer, 0, 0, 800, 600);
 
    // Present frame
    SDL_RenderPresent(renderer);
}
 
SDL_DestroyRenderer(renderer);

Input Handling

Keyboard

SDL_Event event;
while (SDL_PollEvent(&event)) {
    if (event.type == SDL_KEYDOWN) {
        switch (event.key.keysym.sym) {
            case SDLK_ESCAPE: running = false; break;
            case SDLK_LEFT:   player.x -= 5; break;
            case SDLK_RIGHT:  player.x += 5; break;
            case SDLK_UP:     player.y -= 5; break;
            case SDLK_DOWN:   player.y += 5; break;
        }
    }
}
 
// Continuous key state (for smooth movement)
const Uint8* keys = SDL_GetKeyboardState(nullptr);
if (keys[SDL_SCANCODE_LEFT])  player.x -= speed;
if (keys[SDL_SCANCODE_RIGHT]) player.x += speed;

Mouse

SDL_Event event;
while (SDL_PollEvent(&event)) {
    if (event.type == SDL_MOUSEBUTTONDOWN) {
        if (event.button.button == SDL_BUTTON_LEFT) {
            int x = event.button.x;
            int y = event.button.y;
            SDL_Log("Clicked at %d, %d", x, y);
        }
    }
    if (event.type == SDL_MOUSEMOTION) {
        int mx = event.motion.x;
        int my = event.motion.y;
    }
}

Textures & Images (SDL_image)

#include <SDL2/SDL_image.h>
 
// Initialize SDL_image
IMG_Init(IMG_INIT_PNG | IMG_INIT_JPG);
 
// Load image as texture
SDL_Surface* surface = IMG_Load("player.png");
SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, surface);
SDL_FreeSurface(surface);
 
// Draw texture
SDL_Rect src = {0, 0, 64, 64};   // source rect (sprite sheet)
SDL_Rect dst = {100, 100, 64, 64}; // destination on screen
SDL_RenderCopy(renderer, texture, &src, &dst);
 
// Rotate & flip
SDL_RenderCopyEx(renderer, texture, &src, &dst,
    45.0,              // rotation angle (degrees)
    nullptr,           // rotation center (nullptr = center)
    SDL_FLIP_NONE      // SDL_FLIP_HORIZONTAL, SDL_FLIP_VERTICAL
);
 
SDL_DestroyTexture(texture);
IMG_Quit();

Audio (SDL_mixer)

#include <SDL2/SDL_mixer.h>
 
// Initialize mixer
Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 2048);
 
// Load and play music (loops)
Mix_Music* music = Mix_LoadMUS("background.ogg");
Mix_PlayMusic(music, -1); // -1 = loop forever
 
// Load and play sound effect
Mix_Chunk* sfx = Mix_LoadWAV("jump.wav");
Mix_PlayChannel(-1, sfx, 0); // -1 = first free channel
 
// Volume (0-128)
Mix_VolumeMusic(64);
 
// Cleanup
Mix_FreeChunk(sfx);
Mix_FreeMusic(music);
Mix_CloseAudio();

Delta Time & Frame Rate

Uint32 lastTime = SDL_GetTicks();
 
while (running) {
    Uint32 currentTime = SDL_GetTicks();
    float deltaTime = (currentTime - lastTime) / 1000.0f; // seconds
    lastTime = currentTime;
 
    // Move at 200 pixels/second regardless of frame rate
    player.x += 200.0f * deltaTime;
 
    // Cap to ~60 FPS
    SDL_Delay(16);
}

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