Relative mouse mode drag does not report mouse button state.

[mcourteaux]

I have implemented a slider which supports relative mouse mode, to drag more precise than the pixels on the screen. The SDL_MouseMotionEvent::state field loses its mouse button flags when enabling relative mouse mode in Wayland and XWayland. I did not experience this issue before migrating from SDL2 to SDL3.

Eyeballing the code (without proper debugging so far), I'm a bit suspicious about these:

SDL/src/events/SDL_mouse.c

Lines 741 to 744 in 4612db2

	if ((!mouse->relative_mode || mouse->warp_emulation_active) && mouseID != SDL_TOUCH_MOUSEID) {
	// We're not in relative mode, so all mouse events are global mouse events
	mouseID = SDL_GLOBAL_MOUSE_ID;
	}

SDL/src/events/SDL_mouse.c

Lines 932 to 937 in 4612db2

	if (!mouse->relative_mode && mouseID != SDL_TOUCH_MOUSEID) {
	// We're not in relative mode, so all mouse events are global mouse events
	mouseID = SDL_GLOBAL_MOUSE_ID;
	}
	source = GetMouseInputSource(mouse, mouseID, down, button);

This suggests that if we enter relative mouse mode, there is a different SDL_MouseID used. I fear that that might cause it to keep track of the button state in a different SDL_MouseInputSource, which gets obtained here:

SDL/src/events/SDL_mouse.c

Line 849 in 4612db2

event.motion.state = SDL_GetMouseButtonState(mouse, mouseID, true);