Fix Viewport mouse enter+exit notifications

[Sauermann]

resolve #57762

Viewports of a Window receive the notifications NOTIFICATION_WM_MOUSE_ENTER, NOTIFICATION_WM_MOUSE_EXIT, and NOTIFICATION_WM_WINDOW_FOCUS_OUT directly from their window:

godot/scene/main/window.cpp

Lines 326 to 327 in aa069a4

	void Window::_propagate_window_notification(Node *p_node, int p_notification) {
	p_node->notification(p_notification);

Since SubViewports, that are child-nodes of a SubViewportContainer, do not have a Window, they do not receive these events, which leads to the mentioned bug.
This pull request solves this problem by propagating the notifications of SubViewportContainer to their SubViewports.

[reduz]

Looks quite good. @KoBeWi what do you think of it?

[KoBeWi]

This fixes the entered signals, but exit signals seem to be the same. Is this expected?

[Sauermann]

@KoBeWi yes, this is expected. This is a different bug and it is tracked in #28833.
Regarding exit events, this pull request fixes, that they no longer get dropped.

[KoBeWi]

And what about NOTIFICATION_WM_WINDOW_FOCUS_IN? If out is received, so should in, no?

[Sauermann]

Viewport::_notification does not act on NOTIFICATION_WM_WINDOW_FOCUS_IN so I thought, there is no need to forward it.

[KoBeWi]

It doesn't act, but the notification is still received and can be used in scripts etc. So it should be forwarded too.

[Sauermann]

@KoBeWi Ok, I will include that notification. Are there any additional notifications, that should be forwarded?

For windows, I found the following notifications:
NOTIFICATION_WM_CLOSE_REQUEST
NOTIFICATION_WM_GO_BACK_REQUEST
NOTIFICATION_WM_DPI_CHANGE
NOTIFICATION_WM_SIZE_CHANGED

NOTIFICATION_RESIZED is already handled in SubViewportContainer, but for the others I believe that there is no fitting notification in SubViewportContainer.

[KoBeWi]

Are there any additional notifications, that should be forwarded? For windows, I found the following notifications:
NOTIFICATION_WM_CLOSE_REQUEST
NOTIFICATION_WM_GO_BACK_REQUEST
NOTIFICATION_WM_DPI_CHANGE

I don't think these need to be forwarded.

But now that I look at this PR, it sends window-related notifications based on different notifications. I wonder if this should be documented, as users might find it unexpected.

[Sauermann]

it sends window-related notifications based on different notifications

I find it confusing, that NOTIFICATION_WM_MOUSE_ENTER is considered a window-related notification. It doesn't trigger, when the mouse enters the window (which can have a title-bar), but when the mouse enters the viewport of the window. To me it would make more sense, if this notification was considered a viewport-related notification.

I see a problem with the current patch. I believe, that NOTIFICATION_FOCUS_EXIT should not be forwarded as NOTIFICATION_WM_WINDOW_FOCUS_OUT.

NOTIFICATION_WM_WINDOW_FOCUS_OUT means that the window no longer has focus.
NOTIFICATION_FOCUS_EXIT means that a Control no longer has the status of key_focus.
These are two different things and seem to be incompatible.

[Sauermann]

My updated pull request uses different notifications for two concepts:

• mouse being over the window (global state for all nodes) (just as before)
• mouse being over a viewport (viewport-local state) (newly introduced notification)

Otherwise the global state would interfere with subviewports.

[reduz]

Some notes of concern here that I was thinking, the WM focus in and out notifications are propagated through the whole tree to all nodes. I have my doubts whether this is really useful, maybe they should be signals of SceneTree. The problem though is that here the sub-viewport will receive them now.

The problem here is that the WM notifications will be received twice by the sub-viewport.

[Sauermann]

When I noticed, that WM-mouse-enter+exit is distributed to all Nodes, I became aware, that my initial solution would not work. In the most recent patch, I created new notifications, that trigger when the mouse enters a viewport.
For the root-viewport, this notification comes from the Window.
For other sub-viewports, this notification comes from their parent SubViewportContainer.

[reduz]

This makes sense, I am still unhappy to have it in Node, but Viewport has no notifications so not much we can do for the time being.

[akien-mga]

Thanks!