用 SDL2 平铺背景并显示前景

环境：SDL2 + VC++2015

下面的代码将打开background.bmp和image.bmp，将background平铺背景，将image作为前景呈现

  1 #include <iostream>
  2 #include "SDL.h"
  3
  4 //屏幕宽度
  5 const int SCREEN_WIDTH = 640;
  6 const int SCREEN_HEIGHT = 480;
  7
  8 //全局窗口和渲染器
  9 SDL_Window *window = nullptr;
 10 SDL_Renderer *renderer = nullptr;
 11
 12 //加载图片
 13 SDL_Texture* LoadImage(std::string file)
 14 {
 15     SDL_Surface *loadedImage = nullptr;
 16     SDL_Texture *texture = nullptr;
 17
 18     loadedImage = SDL_LoadBMP(file.c_str());
 19     if (loadedImage != nullptr)
 20     {
 21         texture = SDL_CreateTextureFromSurface(renderer, loadedImage);
 22         SDL_FreeSurface(loadedImage);
 23     }
 24     else
 25         std::cout << SDL_GetError() << std::endl;
 26     return texture;
 27 }
 28
 29 //将表面应用到渲染器
 30 void ApplySurface(int x, int y, SDL_Texture *tex, SDL_Renderer *rend)
 31 {
 32     SDL_Rect pos;
 33     pos.x = x;
 34     pos.y = y;
 35     SDL_QueryTexture(tex, NULL, NULL, &pos.w, &pos.h);
 36     SDL_RenderCopy(rend, tex, NULL, &pos);
 37 }
 38
 39 int main(int argc, char** argv)
 40 {
 41     //初始化SDL
 42     if (SDL_Init(SDL_INIT_EVERYTHING) == -1)
 43     {
 44         std::cout << SDL_GetError() << std::endl;
 45         return 1;
 46     }
 47
 48     //创建窗口
 49     window = SDL_CreateWindow("Lesson 2",
 50         SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
 51         SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
 52     if (window == nullptr)
 53     {
 54         std::cout << SDL_GetError() << std::endl;
 55         return 2;
 56     }
 57
 58     //创建渲染器
 59     renderer = SDL_CreateRenderer(window, -1,
 60         SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
 61     if (renderer == nullptr)
 62     {
 63         std::cout << SDL_GetError() << std::endl;
 64         return 3;
 65     }
 66
 67     //创建背景和前景纹理
 68     SDL_Texture *background = nullptr, *image = nullptr;
 69     background = LoadImage("background.bmp");
 70     image = LoadImage("image.bmp");
 71     if (background == nullptr || image == nullptr)
 72         return 4;
 73
 74     //清空渲染器
 75     SDL_RenderClear(renderer);
 76
 77     //在渲染器内平铺背景
 78     int bW, bH;
 79     SDL_QueryTexture(background, NULL, NULL, &bW, &bH);
 80     ApplySurface(0, 0, background, renderer);
 81     ApplySurface(bW, 0, background, renderer);
 82     ApplySurface(0, bH, background, renderer);
 83     ApplySurface(bW, bH, background, renderer);
 84
 85     //在渲染器中央放置前景
 86     int iW, iH;
 87     SDL_QueryTexture(image, NULL, NULL, &iW, &iH);
 88     int x = SCREEN_WIDTH / 2 - iW / 2;
 89     int y = SCREEN_HEIGHT / 2 - iH / 2;
 90     ApplySurface(x, y, image, renderer);
 91
 92     //呈现渲染器
 93     SDL_RenderPresent(renderer);
 94     SDL_Delay(2000);
 95
 96     //释放资源
 97     SDL_DestroyTexture(background);
 98     SDL_DestroyTexture(image);
 99     SDL_DestroyRenderer(renderer);
100     SDL_DestroyWindow(window);
101
102     SDL_Quit();
103
104     return 0;
105 }

彩蛋：

如果窗口变成了1920*1080呢？上面的平铺方法就不够灵活了。试下：

1     int bW, bH;
2     SDL_QueryTexture(background, NULL, NULL, &bW, &bH);
3     for (int y = 0; y <= SCREEN_HEIGHT; y += bH)
4         for (int x = 0; x <= SCREEN_WIDTH; x += bW)
5             ApplySurface(x, y, background, renderer);