Manage Input Focus for Windows from Other Libraries

SDL is primarily designed to manage windows and input for windows it creates itself.

However, it is not straightforward to manage input focus for windows created by other libraries or frameworks using SDL. SDL's functions for window and input management typically expect windows that were created through SDL itself.

Challenges

• Window Handles: SDL manages windows using its own SDL_Window structure. Windows created by other libraries or frameworks do not have this structure.
• Platform-Specific APIs: You would need to use platform-specific APIs to interact with windows created by other libraries. For instance, on Windows, you might use the Win32 API, while on macOS and Linux, you would use their respective APIs.

Interoperability Solutions

While SDL cannot directly manage input focus for non-SDL windows, you can work around this by using native APIs to control focus. Here’s how you might do it on Windows:

1#include <windows.h>
2
3#include <iostream>
4
5int main() {
6  // Assume `hwnd` is the handle to a window
7  // created by another library
8  HWND hwnd = FindWindow(
9    nullptr, "Non-SDL Window Title");
10
11  if (hwnd != nullptr) {
12    SetForegroundWindow(hwnd);  
13    SetFocus(hwnd);             
14  } else {
15    std::cout << "Window not found";
16  }
17}

Integrating with SDL

If you need to integrate such functionality with an SDL application, you might create a hybrid system where SDL manages some windows while others are managed by different libraries.

For example, you could use SDL for rendering and input for your main application window, but manage overlay or auxiliary windows using platform-specific code. Here’s an example:

1#include <SDL.h>
2#include <windows.h>
3#include <iostream>
4
5class SDLWindow {
6 public:
7  SDLWindow() {
8    SDL_Init(SDL_INIT_VIDEO);
9    MainWindow = SDL_CreateWindow(
10      "SDL Window",
11      100, 100, 800, 600,
12      SDL_WINDOW_SHOWN
13    );
14  }
15
16  ~SDLWindow() {
17    SDL_DestroyWindow(MainWindow);
18    SDL_Quit();
19  }
20
21  void SetFocusToOtherWindow(const char* title) {
22    HWND hwnd = FindWindow(nullptr, title);
23    if (hwnd != nullptr) {
24      SetForegroundWindow(hwnd);  
25      SetFocus(hwnd);             
26    } else {
27      std::cout << "Window not found";
28    }
29  }
30
31  SDL_Window* MainWindow{nullptr};
32};
33
34int main(int argc, char** argv) {
35  SDLWindow sdlWindow;
36  SDL_Event Event;
37
38  while (true) {
39    while (SDL_PollEvent(&Event)) {
40      if (Event.type == SDL_QUIT) {
41        return 0;
42      }
43    }
44
45    // Set focus to another window every 5 seconds
46    SDL_Delay(5000);
47    sdlWindow.SetFocusToOtherWindow(
48      "Other Window Title");  
49  }
50  
51  return 0;
52}

Summary

• Limitations: SDL cannot directly manage windows created by other libraries.
• Workarounds: Use platform-specific APIs to interact with non-SDL windows.
• Hybrid Systems: Combine SDL with native API calls for advanced window management scenarios.

Managing input focus for windows created by other libraries requires careful integration of SDL and platform-specific APIs.