Inconsistency between `SDL_GetGlobalMouseState` position and `SDL_GetWindowPosition` on Emscripten

[vittorioromeo]

Hi, I am working on a fork of SFML that uses SDL3 as the backend for windows, joystick, and more.

I reimplemented the sf::Mouse::getPosition API as follows:

Vector2i getPosition()
{
    Vector2f result;
    SDL_GetGlobalMouseState(&result.x, &result.y);
    return result.toVector2i();
}

Vector2i getPosition(const WindowBase& relativeTo)
{
    return getMousePosition() - relativeTo.getPosition();
//                              ^~~~~~~~~~~~~~~~~~~~~~~~
//                       uses SDL_GetWindowPosition() internally
}

This works well on every platform I've tested except Emscripten, where it seems that the getPosition(const WindowBase&) overload returns an incorrect position. More precisely, it seems that getPosition() returns coordinates relative to the canvas in the webpage, and SDL_GetWindowPosition() does the same, therefore the final computed position is incorrect.

I've managed to work around the issue like this:

Vector2i getPosition(const WindowBase& relativeTo)
{
#ifdef SFML_SYSTEM_EMSCRIPTEN
    return getPosition(); 
#else
    return getPosition() - relativeTo.getPosition();
//                         ^~~~~~~~~~~~~~~~~~~~~~~~
//                  uses SDL_GetWindowPosition() internally
#endif
}

But it does seem that this is an inconsistency in SDL3.

[vittorioromeo]

This still seems to be broken for me after merging both #12669 and #12575. The relative mouse position is reported incorrectly -- see this GIF:

https://i.imgur.com/sqBYbwe.mp4

This is my logic:

////////////////////////////////////////////////////////////
Vector2i getPosition()
{
    Vector2f result;
    SDL_GetGlobalMouseState(&result.x, &result.y);
    return result.toVector2i();
}


////////////////////////////////////////////////////////////
Vector2i getPosition(const WindowBase& relativeTo)
{
    return getPosition() - relativeTo.getPosition();
}