Introduction to SDL_Image

Implementing an Image Caching System with SDL_Image

How do I implement a basic image caching system using SDL_Image to improve performance?

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Implementing a basic image caching system using SDL_Image can significantly improve performance, especially when you're frequently loading the same images. Here's a step-by-step guide to create an efficient image caching system:

1. Create a Cache Structure

First, let's define a structure to hold our cached images. We'll use an std::unordered_map for fast lookups:

#include <SDL.h>
#include <SDL_image.h>

#include <iostream>
#include <string>
#include <unordered_map>

struct ImageCache {
  std::unordered_map<std::string, SDL_Surface*>
  surfaces;
  std::unordered_map<std::string, SDL_Texture*>
  textures;
};

2. Implement Cache Functions

Now, let's create functions to load images into the cache and retrieve them:

SDL_Surface* getCachedSurface(
  ImageCache& cache,
  const std::string& filename) {
  auto it = cache.surfaces.find(filename);
  if (it != cache.surfaces.end()) {
    return it->second;
  }

  SDL_Surface* surface = IMG_Load(
    filename.c_str());
  if (surface) {
    cache.surfaces[filename] = surface;
  } else {
    std::cout << "Failed to load image: " <<
      filename << '\n';
  }
  return surface;
}

SDL_Texture* getCachedTexture(
  ImageCache& cache, SDL_Renderer* renderer,
  const std::string& filename) {
  auto it = cache.textures.find(filename);
  if (it != cache.textures.end()) {
    return it->second;
  }

  SDL_Surface* surface = getCachedSurface(
    cache, filename);
  if (!surface) { return nullptr; }

  SDL_Texture* texture =
    SDL_CreateTextureFromSurface(
      renderer, surface);
  if (texture) {
    cache.textures[filename] = texture;
  } else {
    std::cout << "Failed to create texture: " <<
      SDL_GetError() << '\n';
  }
  return texture;
}

3. Implement Cache Cleanup

To prevent memory leaks, we need a function to clean up our cache:

void clearImageCache(ImageCache& cache) {
  for (auto& pair : cache.surfaces) {
    SDL_FreeSurface(pair.second);
  }
  cache.surfaces.clear();

  for (auto& pair : cache.textures) {
    SDL_DestroyTexture(pair.second);
  }
  cache.textures.clear();
}

4. Using the Cache

Now we can use our cache in our main program:

int main() {
  SDL_Init(SDL_INIT_VIDEO);
  IMG_Init(IMG_INIT_PNG | IMG_INIT_JPG);

  SDL_Window* window =
    SDL_CreateWindow("Image Cache Example",
                     SDL_WINDOWPOS_UNDEFINED,
                     SDL_WINDOWPOS_UNDEFINED,
                     640, 480, 0);
  SDL_Renderer* renderer = SDL_CreateRenderer(
    window, -1, 0);

  ImageCache cache;

  // Load and render images
  SDL_Texture* texture1 = getCachedTexture(
    cache, renderer, "image1.png");
  SDL_Texture* texture2 = getCachedTexture(
    cache, renderer, "image2.png");

  SDL_RenderClear(renderer);
  SDL_RenderCopy(renderer, texture1, nullptr,
                 nullptr);
  SDL_RenderPresent(renderer);

  SDL_Delay(2000); // Display for 2 seconds

  SDL_RenderClear(renderer);
  SDL_RenderCopy(renderer, texture2, nullptr,
                 nullptr);
  SDL_RenderPresent(renderer);
  
  // Display for 2 seconds
  SDL_Delay(2000);
  
  // Cleanup
  clearImageCache(cache);
  SDL_DestroyRenderer(renderer);
  SDL_DestroyWindow(window);
  IMG_Quit();
  SDL_Quit();

  return 0;
}

5. Optimizations and Considerations

  • Texture Format: Consider converting surfaces to a consistent texture format when caching to optimize rendering.
  • Cache Size Limit: Implement a maximum cache size and an eviction policy (e.g., least recently used) to prevent excessive memory usage.
  • Thread Safety: If your application is multi-threaded, make sure to add proper synchronization to the cache access functions.
  • Error Handling: Implement more robust error handling and logging for production use.
This Question is from the Lesson:

Introduction to SDL_Image

Learn to load, manipulate, and save various image formats using SDL_Image.

Answers to questions are automatically generated and may not have been reviewed.

This Question is from the Lesson:

Introduction to SDL_Image

Learn to load, manipulate, and save various image formats using SDL_Image.

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