基于 SDL2 的事件驱动编程

Posted 2020-07-21

其实没必要说得太复杂...就是读取用户输入啦。

沿用上一篇的代码，加入事件轮询。

环境：SDL2 + VC++2015

下面的代码将打开background.png和event.png，将background平铺背景，将event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 4 - Event Driven Programming",
 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("event.png");
 68     }
 69     catch (const std::runtime_error &e) {
 70         std::cout << e.what() << std::endl;
 71         return 4;
 72     }
 73 
 74     bool quit = false;
 75     SDL_Event e;
 76     //主循环（CPU高占用）
 77     while (!quit) 
 78     {
 79         //轮询事件栈e
 80         while (SDL_PollEvent(&e))
 81         {
 82             //用户关闭窗口
 83             if (e.type == SDL_QUIT) quit = true;
 84 
 85             //用户按下键盘
 86             if (e.type == SDL_KEYDOWN) quit = true;
 87 
 88             //用户点击鼠标
 89             if (e.type == SDL_MOUSEBUTTONDOWN) quit = true;
 90 
 91             //清空渲染器
 92             SDL_RenderClear(renderer);
 93 
 94             //在渲染器内平铺背景
 95             int bW, bH;
 96             SDL_QueryTexture(background, NULL, NULL, &bW, &bH);
 97             for (int y = 0; y <= SCREEN_HEIGHT; y += bH)
 98                 for (int x = 0; x <= SCREEN_WIDTH; x += bW)
 99                     ApplySurface(x, y, background, renderer);
100 
101 
102             //在渲染器中央放置前景
103             int iW, iH;
104             SDL_QueryTexture(image, NULL, NULL, &iW, &iH);
105             int x = SCREEN_WIDTH / 2 - iW / 2;
106             int y = SCREEN_HEIGHT / 2 - iH / 2;
107             ApplySurface(x, y, image, renderer);
108 
109             //呈现渲染器
110             SDL_RenderPresent(renderer);
111         }
112     }
113 
114     //释放资源
115     SDL_DestroyTexture(background);
116     SDL_DestroyTexture(image);
117     SDL_DestroyRenderer(renderer);
118     SDL_DestroyWindow(window);
119 
120     SDL_Quit();
121 
122     return 0;
123 }