Drop physics mouseover as soon as the mouse moves over a Control

[Sauermann]

fix #61924
alternative to #68018

_drop_physics_mouseover() was added into set_input_as_handled as a fix for #29575 to drop physics mouseover when the mouse is over a control.
The current implementation however doesn't check, if the mouse is actually over a Control, which leads to #61924, where physics-mouseover is dropped even if the mouse is not over a Control.
This patch changes the behavior, so that it is verified that the mouse is actually over a Control, before dropping physics mouseover.
This patch doesn't call _drop_physics_mouseover() in set_input_as_handled but as soon as the mouse enters the area of a Control.

[Sauermann]

It should be safe to cherry-pick this for Godot 3.

[RandomShaper]

I think there's something fishy in all this, but for the time being I can't propose anything better than this patch. I hope at some point I can really look deeply into some of the corner cases and hard edges of input handling that don't quite settle as robust enough to me.

[Sauermann]

@RandomShaper
Thinking about it, this could be a different - maybe more robust - approach (will test it later):
This will drop physics mouse-over whenever the mouse moves on a Control, so that the physics-mouseover is dropped, before the Controls receive their MOUSE_ENTER notification.
This change is closely related to #67791.

diff --git a/scene/main/viewport.cpp b/scene/main/viewport.cpp
index 43a2c9473e..ddf9cac7dd 100644
--- a/scene/main/viewport.cpp
+++ b/scene/main/viewport.cpp
@@ -1669,6 +1669,9 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
                        _gui_cancel_tooltip();
 
                        if (over) {
+                               if (!gui.mouse_over) {
+                                       _drop_physics_mouseover();
+                               }
                                _gui_call_notification(over, Control::NOTIFICATION_MOUSE_ENTER);
                                gui.mouse_over = over;
                        }
@@ -3039,8 +3042,6 @@ bool Viewport::gui_is_drag_successful() const {
 }
 
 void Viewport::set_input_as_handled() {
-       _drop_physics_mouseover();
-
        if (!handle_input_locally) {
                ERR_FAIL_COND(!is_inside_tree());
                Viewport *vp = this;

[Sauermann]

I have updated this patch with the mentioned change. This is a better method, because

• in the previous solution _drop_physics_mouseover was called during every set_input_as_handled, even for events, that have no impact on physics-mouseover
• in the new solution _drop_physics_mouseover is called only once, when the mouse moves to the area of a Control, and not for every mouse-move-event.

That way the previously reported issue #29575 doesn't get reintroduced, while #61924 still gets solved. This kind of reverts #29579.

[RandomShaper]

Looks good.

[akien-mga]

Thanks!