Clear drag preview nodes on NOTIFICATION_DRAG_END

[ryevdokimov]

This didn't really work before. It took seconds for the preview node to actually delete when 'ui_cancel' was pressed before dropping, and there are certain situations where you could keep the preview node in the viewport indefinitely, such as panning around.

2D Before:

2024-01-12.12-53-53.mp4

2D After:

2024-01-12.12-57-40.mp4

3D Before:

2024-01-12.12-55-31.mp4

3D After:

2024-01-12.12-57-51.mp4

[Sauermann]

In its current form, this PR adds an additional call to the Controls can_drop_data() just to check within this call, if ui_cancel is pressed. This adds unnecessary can_drop_data() calls just to get notified, that dragging was cancelled.
When dragging ends, there is a NOTIFICATION_DRAG_END sent to the nodes. It would be better to listen for that notification and do something along the idea of the following lines:

diff --git a/editor/plugins/canvas_item_editor_plugin.cpp b/editor/plugins/canvas_item_editor_plugin.cpp
index f16aff555c..f8f2f0da7d 100644
--- a/editor/plugins/canvas_item_editor_plugin.cpp
+++ b/editor/plugins/canvas_item_editor_plugin.cpp
@@ -6027,6 +6027,10 @@ void CanvasItemEditorViewport::_notification(int p_what) {
                case NOTIFICATION_EXIT_TREE: {
                        disconnect("mouse_exited", callable_mp(this, &CanvasItemEditorViewport::_on_mouse_exit));
                } break;
+
+               case NOTIFICATION_DRAG_END: {
+                       _remove_preview();
+               }
        }
 }

It is likely that with this approach other calls to hide the label could be removed from the code.

This approach has the advantage, that it contains no changes to the viewport core class and aligns with the "Prefer local solutions" best practice.

[ryevdokimov]

That makes a lot of sense, thank you. Changes applied and tested.

[Sauermann]

It looks right, but a review from someone with more expertise regarding editor plugins would help more, since I'm not familiar with them.

changes done.

[KoBeWi]

Commit message/title probably needs a tweak.

[ryevdokimov]

Could be. I'm open to suggestions, how can I improve it?

[KoBeWi]

You could use the title of my PR - "Clear editor drag preview when drag ends".

[ryevdokimov]

Yeah, I can see that.

I wanted to point out this issue occurs specifically when ui_cancel is pressed, but your suggestion explains more directly what is happening. I'll go ahead and change it.

[akien-mga]

Thanks!