How Window IDs Work

When you create a window in SDL using SDL_CreateWindow(), SDL automatically assigns a unique integer ID to that window. This ID, accessible via SDL_GetWindowID(), is crucial for managing multi-window applications.

Why Use Window IDs?

• Event Association: Most events, such as SDL_WINDOWEVENT or SDL_KEYDOWN, include a windowID field. This tells you which window triggered the event.
• Efficient Lookups: With a windowID, you can quickly retrieve the associated SDL_Window* using SDL_GetWindowFromID().
• Multi-Window Management: IDs let you distinguish between windows when handling input, rendering, or custom events.

Example: Retrieve a Window Using an ID

Here’s how to handle an event with its window ID:

1if (event.type == SDL_WINDOWEVENT) {
2  SDL_Window* window = SDL_GetWindowFromID(
3    event.window.windowID);
4  if (window) {
5    std::cout << "Event for window: "
6      << SDL_GetWindowTitle(window) << '\n';
7  }
8}

Multi-Window Use Case

Imagine a painting application with two windows: one for tools and another for the canvas. When a mouse event occurs, the windowID helps determine which window it belongs to:

1void HandleMouseEvent(
2  SDL_MouseButtonEvent& event) {
3  SDL_Window* window = SDL_GetWindowFromID(
4    event.windowID);
5  if (window) {
6    if (SDL_GetWindowTitle(window) ==
7      "Canvas") {
8      std::cout << "Drawing on canvas\n";
9    } else {
10      std::cout << "Clicked on tools window\n";
11    }
12  }
13}

Window IDs make SDL powerful and flexible for applications that require multiple windows.