Mouse vs Input Grabbed
What's the difference between SDL_WINDOW_MOUSE_GRABBED and SDL_WINDOW_INPUT_GRABBED?
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: NoInput 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_GRABBEDfor most use cases - Use
SDL_WINDOW_INPUT_GRABBEDonly 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)
Mouse Input Constraints
Implement mouse constraints in SDL2 to control cursor movement using window grabs and rectangular bounds