Handling Input Focus Changes Triggered by Keyboard Shortcuts

Yes, SDL can handle input focus changes triggered by keyboard shortcuts. You can use SDL's event handling system to capture keyboard shortcuts and then manage the window focus accordingly. Here's how you can achieve this:

First, you need to capture the keyboard shortcuts using SDL's event loop. Here's an example of how you can capture a specific keyboard shortcut (e.g., Ctrl + Tab) to switch focus between windows:

1#include <SDL.h>
2#include <iostream>
3
4class Window {
5public:
6  Window(const char* title,
7    int x, int y, int w, int h) {
8    SDL_Init(SDL_INIT_VIDEO);
9
10    SDLWindow = SDL_CreateWindow(
11      title,
12      x, y, w, h,
13      SDL_WINDOW_SHOWN
14    );
15  }
16
17  ~Window() {
18    SDL_DestroyWindow(SDLWindow);
19    SDL_Quit();
20  }
21
22  SDL_Window* SDLWindow{nullptr};
23};
24
25void HandleKeyboardEvent(
26  SDL_KeyboardEvent& E,
27  Window& window1,
28  Window& window2
29) {
30  const Uint8* state = SDL_GetKeyboardState(nullptr);
31  if (state[SDL_SCANCODE_LCTRL]
32    && state[SDL_SCANCODE_TAB]) {
33    static bool focusOnWindow1 = true;
34    focusOnWindow1 = !focusOnWindow1;
35    std::cout << "Shifting focus to window "
36      << (focusOnWindow1 ? '1' : '2') << '\n';
37    SDL_RaiseWindow(focusOnWindow1
38      ? window1.SDLWindow : window2.SDLWindow); 
39  }
40}
41
42int main(int argc, char** argv) {
43  Window window1("Window 1", 100, 100, 800, 600);
44  Window window2("Window 2", 200, 200, 800, 600);
45  SDL_Event Event;
46
47  while (true) {
48    while (SDL_PollEvent(&Event)) {
49      if (Event.type == SDL_QUIT) {
50        return 0;
51      }
52      if (Event.type == SDL_KEYDOWN) {
53        HandleKeyboardEvent(
54          Event.key, window1, window2);
55      }
56    }
57  }
58  
59  return 0;
60}

1Shifting focus to window 2
2Shifting focus to window 1

Explanation

• Event Loop: The event loop captures all SDL events, including keyboard events.
• Keyboard State: SDL_GetKeyboardState() is used to get the current state of the keyboard. We check if both the Ctrl and Tab keys are pressed.
• Switch Focus: SDL_RaiseWindow() is called to bring the selected window to the front and give it input focus.

You can handle multiple keyboard shortcuts by extending the HandleKeyboardEvent() function to check for different key combinations:

1void HandleKeyboardEvent(
2  SDL_KeyboardEvent& E,
3  Window& window1, Window& window2
4) {
5  const Uint8* state = SDL_GetKeyboardState(nullptr);
6
7  if (state[SDL_SCANCODE_LCTRL]
8    && state[SDL_SCANCODE_TAB]) {
9    static bool focusOnWindow1 = true;
10    focusOnWindow1 = !focusOnWindow1;
11    SDL_RaiseWindow(focusOnWindow1
12      ? window1.SDLWindow
13      : window2.SDLWindow);
14  }
15
16  if (state[SDL_SCANCODE_LALT]
17    && state[SDL_SCANCODE_RETURN]) {
18    SDL_SetWindowFullscreen(
19      window1.SDLWindow,
20      SDL_WINDOW_FULLSCREEN_DESKTOP);  
21  }
22}

• Capture Shortcuts: Use SDL's event loop to capture keyboard shortcuts.
• Get Keyboard State: Use SDL_GetKeyboardState() to check the current state of the keyboard.
• Switch Focus: Use SDL_RaiseWindow() to switch focus between windows.
• Handle Multiple Shortcuts: Extend the event handler to manage multiple keyboard shortcuts.

By capturing and handling keyboard shortcuts, you can effectively manage input focus changes in SDL applications, providing a responsive and user-friendly experience.