I first noticed this in 4.17 while debugging some drag and drop behavior, but it appears to be something more general to mouse position and is still happening in Mac 4.18. I’ve tested on PC builds and this does not occur.
I’m sure there are a bunch of different ways to get at the same result, but here are two different methods I used that demonstrate this issue.
On Mac OS Build 4.18
Follow the instructions here for the drag and drop example project
[Creating Drag and Drop UI | Unreal Engine Documentation][1]
Note that, this documentation is out of date, and instead of overriding “OnMouseDown” you now need to use “OnPreviewMouseDown” as directed in [issue 49100][2]
When Complete, You should notice that when dragging the draggable element, it is significantly offset from the cursor location. When it should be locked to the cursor location. Although weirdly when dropped, the element does use the correct mouse position.
The Second method I used was to simply draw some debug text in HUD that follows the mouse position around.
You should see the offset and between the cursor and where the engine thinks the cursor is, as well as notice the offset seems to increase the further from 0,0 the mouse is.
These methods both behaved correctly in MAC builds 4.16 and older.