Handling SDL Relative Mode Failure
What happens if SDL_SetRelativeMouseMode() fails?
When SDL_SetRelativeMouseMode() fails, it returns a negative value and the system remains in its previous mouse input state. It's crucial to handle this failure gracefully to ensure your application remains usable.
Here's a comprehensive approach to handling relative mode failures:
#include <SDL.h>
#include <iostream>
#include "Window.h"
class MouseController {
public:
bool EnableRelativeMode() {
if (SDL_SetRelativeMouseMode(SDL_TRUE) < 0) {
std::cerr << "Failed to enable relative mode: "
<< SDL_GetError() << '\n';
return false;
}
IsRelative = true;
return true;
}
void HandleFailure() {
// Fall back to normal mouse mode
SDL_SetRelativeMouseMode(SDL_FALSE);
IsRelative = false;
// Notify the user
std::cout << "Using standard mouse mode\n";
}
void Update(SDL_MouseMotionEvent& E) {
if (IsRelative) {
HandleRelativeMotion(E);
} else {
HandleAbsoluteMotion(E);
}
}
private:
void HandleRelativeMotion(SDL_MouseMotionEvent& E) {
// Process relative motion
std::cout << "Relative motion: " << E.xrel
<< ", " << E.yrel << '\n';
}
void HandleAbsoluteMotion(SDL_MouseMotionEvent& E) {
// Process absolute motion
std::cout << "Absolute position: " << E.x
<< ", " << E.y << '\n';
}
bool IsRelative{false};
};
int main() {
SDL_Init(SDL_INIT_VIDEO);
Window GameWindow;
MouseController Mouse;
if (!Mouse.EnableRelativeMode()) {
Mouse.HandleFailure();
}
SDL_Event E;
while (true) {
while (SDL_PollEvent(&E)) {
if (E.type == SDL_MOUSEMOTION) {
Mouse.Update(E.motion);
} else if (E.type == SDL_QUIT) {
SDL_Quit();
return 0;
}
}
GameWindow.Update();
GameWindow.Render();
}
}The key aspects of handling relative mode failure are:
- Always check the return value of
SDL_SetRelativeMouseMode() - Provide a fallback mode that uses standard mouse input
- Inform the user that the system is using fallback behavior
- Ensure your input handling code can work with both relative and absolute mouse input
- Consider providing configuration options to let users manually disable relative mode
Relative Mouse Mode
Learn how to restrict cursor movement to a window whilst capturing mouse motion continuously.