How to access off-cell mouse position inside an EventHandler?

Question

Consider the following example. First, I print the dynamically updated value of the actual position of the mouse, then I print pt, which is the same but is only updated when the EventHandler object (a grey rectangle) is clicked and dragged.

Dynamic@MousePosition@"ScreenScaled"
Dynamic@pt
Deploy@EventHandler[
  Graphics[{Gray, Rectangle[]}, ImageSize -> 50, AspectRatio -> 2],
  {"MouseDragged" :> (pt = MousePosition@"ScreenScaled")}]

This has two issues:

1. While Dynamic@MousePosition@"ScreenScaled" updates correctly when the mouse moves anywhere on the screen, pt is constrained to be updated only in the cell where the EventHandler is when the rectangle is dragged. The EventHandler DOES register and display movement outside the gray Rectangle (and thus outside the EventHandler), though it DOES NOT register movement outside of the cell. Whenever the dragged mouse leaves the cell where the EventHandler resides, the updating stops. Whenever the dragged mouse enters the cell, the updating continues.
2. When the rectangle is dragged, not even Dynamic@MousePosition@"ScreenScaled" gets updated outside of the cell, though it has nothing to do with the EventHandler, and it is updated correctly on its own (i.e. when EventHandler is not triggered).

The problem is more general: the mouse coordinates over the full screen cannot be accessed in any construction I've tried, not just in EventHandlers. Note that MousePosition["coords"] is equivalent to CurrentValue[{"MousePosition","coords"}], and as such, the latter fails as well.

Question: How to access global mouse coordinates in a dynamic structure such as an EventHandler?

EDIT:

What I want is to create an object (e.g. a button) that accepts/processes/displays the global mousecoordinates only when the mouse is dragged.

Answer 1

DynamicModule[{pressed = False},
 Deploy@EventHandler[DynamicWrapper[
    Graphics[{Dynamic[If[pressed, Gray, Black]], Rectangle[]}, 
     ImageSize -> 50, AspectRatio -> 2],
    If[pressed, pt = f[MousePosition@"ScreenScaled"]]
    ],
   {"MouseDown" :> (pressed = True), "MouseUp" :> (pressed = False)}]
 ]

Dynamic@pt

Answer 2

I am still not totally sure that I understand what you want but it seems like you want to be able to drag the mouse anywhere -- not just in a specific event region -- and have those coordinates displayed or do something with the coordinates. If that is the case then I think that NotebookEventAction might be useful. This button toggles between two states:

on = True;
Button["On/Off",
 If[TrueQ[on],
  SetOptions[EvaluationNotebook[], 
   NotebookEventActions :> {"MouseDragged" :> (pt1 = 
        MousePosition@"ScreenScaled")}]; on = ! on,
  SetOptions[EvaluationNotebook[], NotebookEventActions :> {}];
  on = ! on
  ],
 ImageSize -> 100
 ]


Dynamic@pt1

When you switch it on you will find that you can drag the mouse anywhere in the notebook and see the coordinates displayed while the mouse is being dragged. You need to switch this on and off because assigning behaviour to a dragged mouse deactivates the normal mouse dragged functionality -- which is why this is normally confined only to an event region.