用 SDL2 加载PNG平铺背景并显示前景

上一篇中加载的是BMP，这次可以引用 SDL2_image.lib，加载更多格式的图像。

LoadImage函数做了改动，区别在于不用将surface转换成texture了。

环境：SDL2 + VC++2015

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

  1 #include <stdexcept>
  2 #include <string>
  3 #include <iostream>
  4 #include "SDL.h"
  5 #include "SDL_image.h"
  6
  7 //屏幕宽度
  8 const int SCREEN_WIDTH = 1600;
  9 const int SCREEN_HEIGHT = 900;
 10
 11 //全局窗口和渲染器
 12 SDL_Window *window = nullptr;
 13 SDL_Renderer *renderer = nullptr;
 14
 15 //加载图片
 16 SDL_Texture* LoadImage(std::string file)
 17 {
 18     SDL_Texture* tex = nullptr;
 19     tex = IMG_LoadTexture(renderer, file.c_str());
 20     if (tex == nullptr)
 21         throw std::runtime_error("Failed to load image: " + file + IMG_GetError());
 22     return tex;
 23 }
 24
 25 //将表面应用到渲染器
 26 void ApplySurface(int x, int y, SDL_Texture *tex, SDL_Renderer *rend)
 27 {
 28     SDL_Rect pos;
 29     pos.x = x;
 30     pos.y = y;
 31     SDL_QueryTexture(tex, NULL, NULL, &pos.w, &pos.h);
 32     SDL_RenderCopy(rend, tex, NULL, &pos);
 33 }
 34
 35 int main(int argc, char** argv)
 36 {
 37     //初始化SDL
 38     if (SDL_Init(SDL_INIT_EVERYTHING) == -1)
 39     {
 40         std::cout << SDL_GetError() << std::endl;
 41         return 1;
 42     }
 43
 44     //创建窗口
 45     window = SDL_CreateWindow("Lesson 3",
 46         SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
 47         SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
 48     if (window == nullptr)
 49     {
 50         std::cout << SDL_GetError() << std::endl;
 51         return 2;
 52     }
 53
 54     //创建渲染器
 55     renderer = SDL_CreateRenderer(window, -1,
 56         SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
 57     if (renderer == nullptr)
 58     {
 59         std::cout << SDL_GetError() << std::endl;
 60         return 3;
 61     }
 62
 63     //创建背景和前景纹理
 64     SDL_Texture *background = nullptr, *image = nullptr;
 65     try {
 66         background = LoadImage("background.png");
 67         image = LoadImage("image.png");
 68     }
 69     catch (const std::runtime_error &e) {
 70         std::cout << e.what() << std::endl;
 71         return 4;
 72     }
 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     for (int y = 0; y <= SCREEN_HEIGHT; y += bH)
 81         for (int x = 0; x <= SCREEN_WIDTH; x += bW)
 82             ApplySurface(x, y, background, renderer);
 83
 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 }