Creating an Overlay Window in SDL

1#include <SDL.h>
2
3class OverlayWindow {
4public:
5  OverlayWindow() {
6    SDL_Init(SDL_INIT_VIDEO);
7
8    SDLWindow = SDL_CreateWindow(
9      "Overlay Window",
10      SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
11      400, 300,
12      SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALWAYS_ON_TOP 
13    );
14  }
15
16  ~OverlayWindow() {
17    SDL_DestroyWindow(SDLWindow);
18    SDL_Quit();
19  }
20
21  SDL_Window* SDLWindow{nullptr};
22};
23
24int main(int argc, char** argv) {
25  OverlayWindow overlay;
26  SDL_Event Event;
27
28  while (true) {
29    while (SDL_PollEvent(&Event)) {
30      if (Event.type == SDL_QUIT) {
31        return 0;
32      }
33    }
34  }
35  
36  return 0;
37}

1#include <SDL.h>
2#include <SDL_syswm.h>
3#include <windows.h>
4
5class OverlayWindow {
6 public:
7  OverlayWindow() {
8    SDL_Init(SDL_INIT_VIDEO);
9
10    SDLWindow = SDL_CreateWindow(
11      "Overlay Window",
12      SDL_WINDOWPOS_CENTERED,
13      SDL_WINDOWPOS_CENTERED,
14      400, 300,
15      SDL_WINDOW_BORDERLESS
16    );
17
18    HWND hwnd = GetSDLWindowHandle(SDLWindow);
19    SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0,
20                 SWP_NOMOVE | SWP_NOSIZE);  
21  }
22
23  ~OverlayWindow() {
24    SDL_DestroyWindow(SDLWindow);
25    SDL_Quit();
26  }
27
28  SDL_Window* SDLWindow{nullptr};
29
30 private:
31  HWND GetSDLWindowHandle(SDL_Window* window) {
32    SDL_SysWMinfo wmInfo;
33    SDL_VERSION(&wmInfo.version);
34    SDL_GetWindowWMInfo(window, &wmInfo);
35    return wmInfo.info.win.window;
36  }
37};
38
39int main(int argc, char** argv) {
40  OverlayWindow overlay;
41  SDL_Event Event;
42
43  while (true) {
44    while (SDL_PollEvent(&Event)) {
45      if (Event.type == SDL_QUIT) {
46        return 0;
47      }
48    }
49  }
50  
51  return 0;
52}