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。

 #include <stdexcept>
 #include <string>
 #include <iostream>
 #include "SDL.h"
 #include "SDL_image.h"

 //屏幕宽度
 const int SCREEN_WIDTH = ;
 const int SCREEN_HEIGHT = ;

 //全局窗口和渲染器
 SDL_Window *window = nullptr;
 SDL_Renderer *renderer = nullptr;

 //加载图片
 SDL_Texture* LoadImage(std::string file)
 {
     SDL_Texture* tex = nullptr;
     tex = IMG_LoadTexture(renderer, file.c_str());
     if (tex == nullptr)
         throw std::runtime_error("Failed to load image: " + file + IMG_GetError());
     return tex;
 }

 //将表面应用到渲染器
 void ApplySurface(int x, int y, SDL_Texture *tex, SDL_Renderer *rend)
 {
     SDL_Rect pos;
     pos.x = x;
     pos.y = y;
     SDL_QueryTexture(tex, NULL, NULL, &pos.w, &pos.h);
     SDL_RenderCopy(rend, tex, NULL, &pos);
 }

 int main(int argc, char** argv)
 {
     //初始化SDL
     if (SDL_Init(SDL_INIT_EVERYTHING) == -)
     {
         std::cout << SDL_GetError() << std::endl;
         return ;
     }

     //创建窗口
     window = SDL_CreateWindow("Lesson 3",
         SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
         SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
     if (window == nullptr)
     {
         std::cout << SDL_GetError() << std::endl;
         return ;
     }

     //创建渲染器
     renderer = SDL_CreateRenderer(window, -,
         SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
     if (renderer == nullptr)
     {
         std::cout << SDL_GetError() << std::endl;
         return ;
     }

     //创建背景和前景纹理
     SDL_Texture *background = nullptr, *image = nullptr;
     try {
         background = LoadImage("background.png");
         image = LoadImage("image.png");
     }
     catch (const std::runtime_error &e) {
         std::cout << e.what() << std::endl;
         return ;
     }

     //清空渲染器
     SDL_RenderClear(renderer);

     //在渲染器内平铺背景
     int bW, bH;
     SDL_QueryTexture(background, NULL, NULL, &bW, &bH);
     for (int y = ; y <= SCREEN_HEIGHT; y += bH)
         for (int x = ; x <= SCREEN_WIDTH; x += bW)
             ApplySurface(x, y, background, renderer);

     //在渲染器中央放置前景
     int iW, iH;
     SDL_QueryTexture(image, NULL, NULL, &iW, &iH);
     int x = SCREEN_WIDTH /  - iW / ;
     int y = SCREEN_HEIGHT /  - iH / ;
     ApplySurface(x, y, image, renderer);

     //呈现渲染器
     SDL_RenderPresent(renderer);
     SDL_Delay();

     //释放资源
     SDL_DestroyTexture(background);
     SDL_DestroyTexture(image);
     SDL_DestroyRenderer(renderer);
     SDL_DestroyWindow(window);

     SDL_Quit();

     return ;
 }