Size Changed vs Resized Events

Both SDL_WINDOWEVENT_SIZE_CHANGED and SDL_WINDOWEVENT_RESIZED are window events related to size changes, but they differ in when and how they are triggered.

SDL_WINDOWEVENT_SIZE_CHANGED

This event occurs when the window size changes and rendering must be updated. It’s typically triggered after the user completes a resize action or when the window is resized programmatically using functions like SDL_SetWindowSize().

Here’s how you might handle it:

1if (event.type == SDL_WINDOWEVENT &&
2    event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
3  int width = event.window.data1;
4  int height = event.window.data2;
5  std::cout << "Size changed to: "
6    << width << "x" << height << "\n";
7}

SDL_WINDOWEVENT_RESIZED

This event is sent more broadly and includes platform-specific behavior. It’s triggered whenever a resize operation occurs, including intermediate steps while the user is actively resizing the window.

To handle this:

1if (event.type == SDL_WINDOWEVENT &&
2    event.window.event == SDL_WINDOWEVENT_RESIZED) {
3  int width = event.window.data1;
4  int height = event.window.data2;
5  std::cout << "Resizing in progress: "
6    << width << "x" << height << "\n";
7}

Key Differences

• Frequency: SDL_WINDOWEVENT_RESIZED fires multiple times during a resize operation, while SDL_WINDOWEVENT_SIZE_CHANGED fires once after the size stabilizes.
• Purpose: Use SDL_WINDOWEVENT_RESIZED for tasks like logging or real-time feedback, and SDL_WINDOWEVENT_SIZE_CHANGED for updating rendering or layouts after resizing.

By distinguishing between these events, you can optimize your application’s response to resizing and avoid unnecessary recalculations or redraws.