Since the frame is "Frameless" the trick is to compute the true WindowSize from the WindowMargins:
trueWindowSize[
marg : {{_, _}, {_, _}},
rec : {{_, _}, {_, _}} | Automatic : Automatic
] :=
With[
{
sr =
Replace[rec,
Automatic :>
Lookup[
AbsoluteOptions[$FrontEnd, ScreenRectangle],
ScreenRectangle
]
]
},
{
(sr[[1, 2]] - marg[[1, 2]]) -
(sr[[1, 1]] + marg[[1, 1]]),
sr[[2, 2]] - marg[[2, 2]] -
(sr[[2, 1]] + marg[[2, 1]])
}
];
trueWindowSize[
nb_NotebookObject,
rec : {{_, _}, {_, _}} | Automatic : Automatic
] :=
trueWindowSize[AbsoluteCurrentValue[nb, WindowMargins], rec]
Then:
nb = CreateDocument[];
di =
CreateDocument["",
WindowSize -> trueWindowSize[nb],
WindowMargins -> AbsoluteCurrentValue[nb, WindowMargins],
WindowElements -> None,
WindowFrameElements -> None,
WindowFrame -> "Frameless",
WindowOpacity -> .5,
Background -> Blue
]
Extended Answer:
But there are subtleties here to explore.
To illustrate this, let's compute the WindowSize and WindowMargins for a pile of different window configurations:
windowSize[frame_, elems_, frelems_, close : True | False : True] :=
With[{
sr =
Lookup[
AbsoluteOptions[$FrontEnd, ScreenRectangle],
ScreenRectangle
],
nb =
CreateDocument[
Panel["", Background -> Yellow, ImageSize -> {500, 500}],
WindowSize -> All,
WindowFrame -> frame,
WindowElements -> elems,
WindowFrameElements -> frelems,
Visible -> False
]},
If[close,
NotebookClose[nb];
<|
"GivenSize" -> #[WindowSize],
"TrueSize" -> trueWindowSize[#[WindowMargins], sr]
|>,
{nb,
<|
"GivenSize" -> #[WindowSize],
"TrueSize" -> trueWindowSize[#[WindowMargins], sr]
|>
}
] &@
Association@
AbsoluteOptions[nb, {WindowSize, WindowMargins}]
]
windowSize[a : {, _, _},
b : {, _, _}] :=
(NotebookClose@*First /@ #;
Subtract[#[[1, 2]], #[[2, 2]]]) &@
{
windowSize @@ Append[a, False],
windowSize @@ Append[b, False]
}
windowSizeData =
AssociationMap[
windowSize[#Frame, #Elements, #FrameElements] &,
AssociationThread[
{"Frame", "Elements", "FrameElements"},
#
] & /@
Tuples[
{
{"Frameless", "Generic", "ModalDialog", "ModelessDialog",
"MovableModalDialog", "Normal", "Palette", "ThinFrame"},
Subsets[
{"HorizontalScrollBar", "MagnificationPopUp", "StatusArea",
"VerticalScrollBar"}, 1
],
Subsets[
{"CloseBox", "ZoomBox", "ResizeArea"},
1
]
}
]
];
Then we'll group this by discrepancy between stated and real window size:
GroupBy[Normal[windowSizeData],
(Last[#]["TrueSize"] - Last[#]["GivenSize"] &) -> First] //
KeySort // Map[Take[#, 5] &] // Dataset
And we see the WindowSize discrepancy just comes out of the frame. So when we align notebooks we need to account for that. On the other hand, sometimes we may also want to account for in-frame elements, so here's a comparative way to compute size differences based on frame and elements:
windowSizeAdjustments[
baseStyle :
{_, _, _} :
{Automatic, Automatic, Automatic
},
newStyle :
{_, _, _} :
{"Frameless", None, None}
] :=
windowSizeAdjustments[baseStyle, newStyle] =
Module[{
nb =
CreateDocument[
Panel["",
Background -> Yellow,
ImageSize -> {500, 500}],
Visible -> False,
WindowSize -> All,
WindowFrame -> baseStyle[[1]],
WindowElements -> baseStyle[[2]],
WindowFrameElements -> baseStyle[[3]]
],
base,
frame,
elem
},
base = trueWindowSize[nb];
SetOptions[nb,
{
WindowFrame -> newStyle[[1]],
WindowFrameElements -> None,
WindowElements -> None
}];
frame =
trueWindowSize[nb];
SetOptions[nb,
{
WindowFrame -> baseStyle[[1]],
WindowFrameElements -> newStyle[[2]],
WindowElements -> newStyle[[3]]
}];
elem =
trueWindowSize[nb];
NotebookClose[nb];
<|
"Elements" -> base - elem,
"Frame" -> base - frame
|>
];
windowSizeAdjustments[
nb1 : _Notebook | Automatic : Automatic,
dialog_Notebook
] :=
Module[{
opsBase =
Switch[nb1,
Automatic,
{
WindowFrame -> Automatic,
WindowElements -> Automatic,
WindowFrameElements -> Automatic
},
_Notebook,
Association@Join[Options[Notebook], List @@ Rest[nb1]]
],
ops = Association@Join[Options[Notebook], List @@ Rest[dialog]]
},
windowSizeAdjustments[
{
Lookup[opsBase, WindowFrame, Automatic],
Lookup[opsBase, WindowFrameElements, Automatic],
Lookup[opsBase, WindowElements, Automatic]
},
{
Lookup[ops, WindowFrame, "Frameless"],
Lookup[ops, WindowFrameElements, None],
Lookup[ops, WindowElements, None]
}
]
];
And then we can use this to compute the discrepancy for different notebooks:
nb = Notebook[{}];
di =
Notebook[{},
WindowElements -> None,
WindowFrameElements -> None,
WindowFrame -> "ThinFrame",
WindowOpacity -> .5,
Background -> Blue,
System`CellInsertionPointCell -> None,
System`CellInsertionPointColor -> Blue,
System`BlinkingCellInsertionPoint -> False
];
windowSizeAdjustments[nb, di]
<|"Elements" -> {0, 0}, "Frame" -> {-2, 20}|>
And we can make use of this for any frame style (note, beware of the modal frame styles -- you'll have to quit Mathematica to get rid of them, although usually you can say Cancel at the "Save changes to ..." dialog):
NotebookClose /@ {nbObj, diObj};
nbObj = CreateDocument[nb, WindowSize -> {250, 250}];
diObj =
Block[{frameStyle = "ThinFrame"},
CreateDocument[di,
WindowSize ->
AbsoluteCurrentValue[nbObj, WindowSize] +
windowSizeAdjustments[nb, Insert[di, WindowFrame -> frameStyle]][
"Frame"],
WindowMargins -> AbsoluteCurrentValue[nbObj, WindowMargins],
WindowFrame -> frameStyle
]
]
NotebookClose /@ {nbObj, diObj};
nbObj = CreateDocument[nb, WindowSize -> {250, 250}];
diObj =
Block[{frameStyle = "ModelessDialog"},
CreateDocument[di,
WindowSize ->
AbsoluteCurrentValue[nbObj, WindowSize] +
windowSizeAdjustments[nb, Insert[di, WindowFrame -> frameStyle]][
"Frame"],
WindowMargins -> AbsoluteCurrentValue[nbObj, WindowMargins],
WindowFrame -> frameStyle
]
]
