Preventing a Window from Losing Input Focus in SDL

Preventing a window from losing input focus in SDL can be challenging because focus management is typically handled by the operating system.

However, there are some techniques you can use to minimize focus loss or regain focus quickly.

Using SDL_RaiseWindow()

One way to regain focus quickly is to use the SDL_RaiseWindow() function when the window loses focus. This brings the window to the front and attempts to grab input focus:

1void HandleWindowEvent(SDL_WindowEvent& E) {
2  if (E.event == SDL_WINDOWEVENT_FOCUS_LOST) {
3    std::cout << "Window lost input focus\\n";
4    SDL_RaiseWindow(SDL_GetWindowFromID(E.windowID)); 
5  }
6}

Example Implementation

Here's a full example of how you might implement this in an SDL application:

1#include <SDL.h>
2#include <iostream>
3#include <chrono>
4#include <thread>
5
6class FocusWindow {
7public:
8  FocusWindow() {
9    SDL_Init(SDL_INIT_VIDEO);
10
11    SDLWindow = SDL_CreateWindow(
12      "Focus Window",
13      SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
14      800, 600,
15      SDL_WINDOW_SHOWN
16    );
17  }
18
19  ~FocusWindow() {
20    SDL_DestroyWindow(SDLWindow);
21    SDL_Quit();
22  }
23
24  SDL_Window* SDLWindow{nullptr};
25};
26
27void HandleWindowEvent(SDL_WindowEvent& E) {
28  using namespace std::chrono;
29  if (E.event == SDL_WINDOWEVENT_FOCUS_LOST) {
30    std::cout << "Window lost input focus\n";
31    std::this_thread::sleep_for(milliseconds(500)); 
32    SDL_RaiseWindow(SDL_GetWindowFromID(E.windowID));
33    std::cout << "Input focus restored\n";
34  }
35}
36
37int main(int argc, char** argv) {
38  FocusWindow focusWindow;
39  SDL_Event Event;
40
41  while (true) {
42    while (SDL_PollEvent(&Event)) {
43      if (Event.type == SDL_QUIT) {
44        return 0;
45      }
46      if (Event.type == SDL_WINDOWEVENT) {
47        HandleWindowEvent(Event.window);
48      }
49    }
50  }
51  
52  return 0;
53}

1Window lost input focus
2Input focus restored

Considerations

• User Experience: Constantly regaining focus can be intrusive and frustrating for users. Use this technique sparingly and only when necessary.
• Platform Differences: The effectiveness of regaining focus can vary across different operating systems. Test your application on multiple platforms to ensure consistent behavior.
• Event Throttling: To avoid rapid focus changes, consider adding a delay before regaining focus, as shown in the example above.

Using SDL_Hint

You can set the hint SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS to "0" to prevent a full screen window from being minimized when it loses focus:

1SDL_SetHint(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS, "0");

Summary

• Regain Focus: Use SDL_RaiseWindow() to regain focus when it is lost.
• User Experience: Be mindful of the user experience and avoid intrusive behavior.
• Platform Testing: Ensure consistent behavior across different operating systems.
• Hints: Use SDL hints to adjust focus behavior, such as preventing window minimization.

While preventing focus loss entirely is not feasible, these techniques can help you manage focus more effectively in your SDL application.