SDL2笔记05_SDL2透明背景窗口_windows10_使用sdl_texture绘图

1. 本节课学习使用SDL2封装一个透明背景的window，并在window上使用SDL_Renderer和SDL_Texture进行绘图
   1. 圆形没有反走样
   2. 计算机几何算法B站有个孔令德老师讲课挺好的，建议看看
      （我只看了两节课，后面工作不忙了再认真看，图论与网络流还没开始看，把SDL和GTK大致学一下再去看把，档期可能要排到明年才能开始看了）

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2. 在windows上要想让SDL_Window和linux不太一样（linux可以直接读取css设置）

   1. 经过多次google终于在这个网址找到了做法http://5.9.10.113/67609916/fully-transparent-window-with-opaque-elements-in-sdl-2链接
   2. 以下为代码网址上copy的代码

               #include <stdio.h>
               #include <SDL.h>
               #include <SDL_image.h>
               #include <SDL_syswm.h>
               #include <iostream>
               #include <Windows.h>
               #include <string>
   
               SDL_Window *window;
               SDL_Renderer *renderer;
   
               SDL_Texture *image;
               int imageWidth = 0;
               int imageHeight = 0;
   
               bool init() {
        
                   //Initialize SDL
                   if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        
                       printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
                       return false;
                   }
   
                   //Set texture filtering to linear
                   if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1")) {
        
                       printf("Warning: Linear texture filtering not enabled!");
                   }
   
                   //Create window
                   window = SDL_CreateWindow("SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 500, 300,
                                                SDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS);
                   if (window == NULL) {
        
                       printf("Window could not be created! SDL Error: %s\n", SDL_GetError());
                       return false;
                   }
   
                   //Create renderer for window
                   renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
                   if (renderer == NULL) {
        
                       printf("Renderer could not be created! SDL Error: %s\n", SDL_GetError());
                       return false;
                   }
   
                   //Initialize renderer color
                   SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
   
                   //Initialize PNG loading
                   int imgFlags = IMG_INIT_PNG;
                   if (!(IMG_Init(imgFlags) & imgFlags)) {
        
                       printf("SDL_image could not initialize! SDL_image Error: %s\n", IMG_GetError());
                       return false;
                   }
                   return true;
               }
   
               bool loadImage(const std::string &path) {
        
                   //The final texture
                   SDL_Texture *newImage = NULL;
   
                   //Load image at specified path
                   SDL_Surface *loadedSurface = IMG_Load(path.c_str());
                   if (!loadedSurface) {
        
                       printf("Unable to load image %s! SDL_image Error: %s\n", path.c_str(), IMG_GetError());
                       return false;
                   }
   
                   //Create texture from surface pixels
                   newImage =