Mouse Input Constraints

Mouse vs Input Grabbed

What's the difference between SDL_WINDOW_MOUSE_GRABBED and SDL_WINDOW_INPUT_GRABBED?

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The distinction between SDL_WINDOW_MOUSE_GRABBED and SDL_WINDOW_INPUT_GRABBED is important but subtle. Let's break down the differences and see when to use each.

Mouse Grabbed

SDL_WINDOW_MOUSE_GRABBED only affects mouse input:

  • Constrains the mouse cursor to the window
  • Doesn't affect keyboard input
  • More commonly used in modern applications

Here's an example of mouse-only grabbing:

#include <SDL.h>
#include <iostream>

void PrintGrabState(SDL_Window* Window) {
  bool MouseGrabbed{
    SDL_GetWindowMouseGrab(Window) == SDL_TRUE};
  bool InputGrabbed{
    SDL_GetWindowKeyboardGrab(Window) == SDL_TRUE};

  std::cout << "Mouse Grabbed: "
    << (MouseGrabbed ? "Yes" : "No") << "\n";
  std::cout << "Keyboard Grabbed: "
    << (InputGrabbed ? "Yes" : "No") << "\n";
}

int main(int argc, char** argv) {
  SDL_Init(SDL_INIT_VIDEO);
  SDL_Window* Window{SDL_CreateWindow(
    "Mouse Grab Example",
    100, 100, 800, 600,
    SDL_WINDOW_MOUSE_GRABBED  
  )};

  std::cout << "Initial State:\n";
  PrintGrabState(Window);

  SDL_DestroyWindow(Window);
  SDL_Quit();
  return 0;
}
Initial State:
Mouse Grabbed: Yes
Keyboard Grabbed: No

Input Grabbed

SDL_WINDOW_INPUT_GRABBED is more comprehensive:

  • Grabs both mouse and keyboard input
  • Prevents Alt+Tab and other system key combinations
  • Legacy feature from SDL 1.2, less commonly used now

Here's an example showing the difference:

#include <SDL.h>
#include <iostream>
#include "PrintGrabState.h"

int main(int argc, char** argv) {
  SDL_Init(SDL_INIT_VIDEO);

  // Create two windows to demonstrate
  // the difference
  SDL_Window* MouseWindow{SDL_CreateWindow(
    "Mouse Grabbed Window",
    100, 100, 400, 300,
    SDL_WINDOW_MOUSE_GRABBED
  )};

  SDL_Window* InputWindow{SDL_CreateWindow(
    "Input Grabbed Window",
    500, 100, 400, 300,
    SDL_WINDOW_INPUT_GRABBED
  )};

  // Print state for both windows
  std::cout << "Mouse Grabbed Window:\n";
  PrintGrabState(MouseWindow);

  std::cout << "\nInput Grabbed Window:\n";
  PrintGrabState(InputWindow);

  SDL_DestroyWindow(MouseWindow);
  SDL_DestroyWindow(InputWindow);
  SDL_Quit();
  return 0;
}

Best Practices

In modern applications:

  • Prefer SDL_WINDOW_MOUSE_GRABBED for most use cases
  • Use SDL_WINDOW_INPUT_GRABBED only when you need to capture all input
  • Consider accessibility implications of input grabbing
  • Always provide a way for users to release the grab (like Esc key)

Answers to questions are automatically generated and may not have been reviewed.

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