Managing Window Input Focus

Creating an Overlay Window in SDL

How can I create an overlay window that always stays on top of other windows?

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Creating an overlay window in SDL that always stays on top of other SDL windows involves a combination of SDL window flags and platform-specific techniques.

SDL itself doesn't directly support "always on top" windows, but you can achieve this effect with a few tricks.

Creating the Overlay Window

First, create the window with the appropriate SDL flags. Typically, you would want the window to be borderless to give it an overlay-like appearance:

#include <SDL.h>

class OverlayWindow {
public:
  OverlayWindow() {
    SDL_Init(SDL_INIT_VIDEO);

    SDLWindow = SDL_CreateWindow(
      "Overlay Window",
      SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
      400, 300,
      SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALWAYS_ON_TOP 
    );
  }

  ~OverlayWindow() {
    SDL_DestroyWindow(SDLWindow);
    SDL_Quit();
  }

  SDL_Window* SDLWindow{nullptr};
};

int main(int argc, char** argv) {
  OverlayWindow overlay;
  SDL_Event Event;

  while (true) {
    while (SDL_PollEvent(&Event)) {
      if (Event.type == SDL_QUIT) {
        return 0;
      }
    }
  }
  
  return 0;
}

Platform-Specific Adjustments

To make the window stay on top, you might need to use platform-specific APIs. Here's how you can achieve this on Windows using the Win32 API:

#include <SDL.h>
#include <SDL_syswm.h>
#include <windows.h>

class OverlayWindow {
 public:
  OverlayWindow() {
    SDL_Init(SDL_INIT_VIDEO);

    SDLWindow = SDL_CreateWindow(
      "Overlay Window",
      SDL_WINDOWPOS_CENTERED,
      SDL_WINDOWPOS_CENTERED,
      400, 300,
      SDL_WINDOW_BORDERLESS
    );

    HWND hwnd = GetSDLWindowHandle(SDLWindow);
    SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0,
                 SWP_NOMOVE | SWP_NOSIZE);  
  }

  ~OverlayWindow() {
    SDL_DestroyWindow(SDLWindow);
    SDL_Quit();
  }

  SDL_Window* SDLWindow{nullptr};

 private:
  HWND GetSDLWindowHandle(SDL_Window* window) {
    SDL_SysWMinfo wmInfo;
    SDL_VERSION(&wmInfo.version);
    SDL_GetWindowWMInfo(window, &wmInfo);
    return wmInfo.info.win.window;
  }
};

int main(int argc, char** argv) {
  OverlayWindow overlay;
  SDL_Event Event;

  while (true) {
    while (SDL_PollEvent(&Event)) {
      if (Event.type == SDL_QUIT) {
        return 0;
      }
    }
  }
  
  return 0;
}

In this example, SetWindowPos() is used to set the window as always on top (HWND_TOPMOST).

Considerations

  • Cross-Platform: For a cross-platform solution, you would need to implement similar logic using respective platform-specific APIs for macOS and Linux.
  • User Experience: Always-on-top windows can be intrusive. Ensure this behavior is appropriate for your application's use case.
  • Focus Management: Handle focus and input appropriately. Overlay windows should not disrupt the main application's usability.

Creating an overlay window in SDL involves combining SDL's window creation functions with platform-specific code to achieve the desired always-on-top behavior.

This Question is from the Lesson:

Managing Window Input Focus

Learn how to manage and control window input focus in SDL applications, including how to create, detect, and manipulate window focus states.

Answers to questions are automatically generated and may not have been reviewed.

This Question is from the Lesson:

Managing Window Input Focus

Learn how to manage and control window input focus in SDL applications, including how to create, detect, and manipulate window focus states.

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