[笔记]音视频学习之SDL篇《五》裁剪图片成子图片（裁剪精灵表）

//Start up SDL and make sure it went ok
  if (SDL_Init(SDL_INIT_VIDEO) != 0) {
    logSDLError(std::cout, "SDL_Init");
    return 1;
  }
  //Setup our window and renderer
  SDL_Window* window = SDL_CreateWindow("Lesson 5", SDL_WINDOWPOS_CENTERED,
    SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
  if (window == nullptr) {
    logSDLError(std::cout, "CreateWindow");
    SDL_Quit();
    return 1;
  }
  SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
  if (renderer == nullptr) {
    logSDLError(std::cout, "CreateRenderer");
    cleanup(window);
    SDL_Quit();
    return 1;
  }
  const std::string resPath = getResourcePath("Lesson5");
  SDL_Texture* image = loadTexture("..\\..\\res\\05sdl_learn\\image.png", renderer);
  if (image == nullptr) {
    cleanup(image, renderer, window);
    IMG_Quit();
    SDL_Quit();
    return 1;
  }

int iW = 100, iH = 100;
  int x = SCREEN_WIDTH / 2 - iW / 2;
  int y = SCREEN_HEIGHT / 2 - iH / 2;

//Setup the clips for our image
  SDL_Rect clips[4];
  //Since our clips our uniform in size we can generate a list of their
  //positions using some math (the specifics of this are covered in the lesson)
  for (int i = 0; i < 4; ++i) {
    clips[i].x = i / 2 * iW;
    clips[i].y = i % 2 * iH;
    clips[i].w = iW;
    clips[i].h = iH;
    SDL_Log("(%d,%d)", clips[i].x, clips[i].y);
  }

//Specify a default clip to start with
  int useClip = 0;
  SDL_Event e;
  bool quit = false;
  while (!quit) {
    //Event Polling
    while (SDL_PollEvent(&e)) {
      if (e.type == SDL_QUIT) {
        quit = true;
      }
      //Use number input to select which clip should be drawn
      if (e.type == SDL_KEYDOWN) {
        switch (e.key.keysym.sym) {
        case SDLK_1:
        case SDLK_KP_1:
          useClip = 0;
          break;
        case SDLK_2:
        case SDLK_KP_2:
          useClip = 1;
          break;
        case SDLK_3:
        case SDLK_KP_3:
          useClip = 2;
          break;
        case SDLK_4:
        case SDLK_KP_4:
          useClip = 3;
          break;
        case SDLK_ESCAPE:
          quit = true;
          break;
        default:
          break;
        }
      }
    }
    //Rendering
    SDL_RenderClear(renderer);
    //Draw the image
    renderTexture(image, renderer, x, y, &clips[useClip]);
    //Update the screen
    SDL_RenderPresent(renderer);
  }
  //Clean up
  cleanup(image, renderer, window);
  IMG_Quit();
  SDL_Quit();