Creating an Overlay Window in SDL

1#include <SDL.h>
2
3class OverlayWindow {
4public:
5  OverlayWindow() {
6    SDLWindow = SDL_CreateWindow(
7      "Overlay Window",
8      SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
9      400, 300,
10      SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALWAYS_ON_TOP 
11    );
12  }
13
14  ~OverlayWindow() {
15    SDL_DestroyWindow(SDLWindow);
16  }
17
18  SDL_Window* SDLWindow{nullptr};
19};
20
21int main(int argc, char** argv) {
22  SDL_Init(SDL_INIT_VIDEO);
23  OverlayWindow overlay;
24  SDL_Event Event;
25
26  while (true) {
27    while (SDL_PollEvent(&Event)) {
28      if (Event.type == SDL_QUIT) {
29        return 0;
30      }
31    }
32  }
33  
34  SDL_Quit();
35  return 0;
36}

1#include <SDL.h>
2#include <SDL_syswm.h>
3#include <windows.h>
4
5class OverlayWindow {
6 public:
7  OverlayWindow() {
8    SDLWindow = SDL_CreateWindow(
9      "Overlay Window",
10      SDL_WINDOWPOS_CENTERED,
11      SDL_WINDOWPOS_CENTERED,
12      400, 300,
13      SDL_WINDOW_BORDERLESS
14    );
15
16    HWND hwnd = GetSDLWindowHandle(SDLWindow);
17    SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0,
18                 SWP_NOMOVE | SWP_NOSIZE);  
19  }
20
21  ~OverlayWindow() {
22    SDL_DestroyWindow(SDLWindow);
23  }
24
25  SDL_Window* SDLWindow{nullptr};
26
27 private:
28  HWND GetSDLWindowHandle(SDL_Window* window) {
29    SDL_SysWMinfo wmInfo;
30    SDL_VERSION(&wmInfo.version);
31    SDL_GetWindowWMInfo(window, &wmInfo);
32    return wmInfo.info.win.window;
33  }
34};
35
36int main(int argc, char** argv) {
37  SDL_Init(SDL_INIT_VIDEO);
38  OverlayWindow overlay;
39  SDL_Event Event;
40
41  while (true) {
42    while (SDL_PollEvent(&Event)) {
43      if (Event.type == SDL_QUIT) {
44        return 0;
45      }
46    }
47  }
48  
49  SDL_Quit();
50  return 0;
51}