;WinSetTransColor is better but here's some WinSetRegion test code:

#Requires AutoHotkey 2.0
#SingleInstance Force

; --- PART 1: Example Setup (You will replace this with your actual GUI/Window setup) ---
; Assume these are your main GUI's (the one that will get the hole) details
; These are the screen coordinates and dimensions you used to SHOW your main GUI.
mainX := 100
mainY := 100
mainWidth := 600
mainHeight := 400

mainGui := Gui("-Caption")
mainGui.Title := "Main GUI (Always On Top)"
mainGui.BackColor := "Gray" ; To clearly see the hole
mainGui.Opt("+AlwaysOnTop") ; Make it always on top
mainGui.AddButton("x220 y350 w300", "Refresh e-mails")
mainGui.Show("x" mainX " y" mainY " w" mainWidth " h" mainHeight)

; Assume these are your child window's (the one being covered) details
; These are the screen coordinates and dimensions of the window that will define the hole.
childX := 450
childY := 400
childWidth := 300
childHeight := 150

childGui := Gui("-Caption")
childGui.Title := "Child Window (Visible Through Hole)"
childGui.BackColor := "Navy"
childGui.Add("Text", "cWhite", "I am the child window!")
childGui.Show("x" childX " y" childY " w" childWidth " h" childHeight)

; Give windows a moment to appear
Sleep 100

; --- PART 2: Core Logic to Create the Hole in mainGui ---

; IMPORTANT: Get the *current actual screen position* of the main GUI.
; This is important in case it was moved after being shown.
WinGetPos(&CurrentMainScreenX, &CurrentMainScreenY, &CurrentMainWidth, &CurrentMainHeight, "ahk_id " mainGui.Hwnd)


; 1. Calculate the hole's coordinates *relative to the main GUI's top-left corner (0,0)*
; The WinSetRegion command expects relative coordinates for both the outer and inner polygons.
HoleLeftRelative := childX - CurrentMainScreenX
HoleTopRelative := childY - CurrentMainScreenY
HoleRightRelative := HoleLeftRelative + childWidth
HoleBottomRelative := HoleTopRelative + childHeight

; 2. Construct the outer polygon string (representing the entire main GUI)
; Coordinates are 0-0 up to its current actual width and height.
OuterPolygonString := "0-0 " CurrentMainWidth "-0 " CurrentMainWidth "-" CurrentMainHeight " 0-" CurrentMainHeight " 0-0"

; 3. Construct the inner polygon string (representing the hole)
InnerPolygonString := ""
InnerPolygonString .= HoleLeftRelative "-" HoleTopRelative " "
InnerPolygonString .= HoleRightRelative "-" HoleTopRelative " "
InnerPolygonString .= HoleRightRelative "-" HoleBottomRelative " "
InnerPolygonString .= HoleLeftRelative "-" HoleBottomRelative " "
InnerPolygonString .= HoleLeftRelative "-" HoleTopRelative ; Close the polygon

; 4. Combine the outer and inner polygons into the final region string
RegionStringForWinSetRegion := OuterPolygonString "   " InnerPolygonString

; 5. Apply the region to your main GUI
WinSetRegion(RegionStringForWinSetRegion, "ahk_id " mainGui.Hwnd)

; --- PART 3: Event Handlers (for clean exit) ---
mainGui_OnClose() {
    ExitApp
}

childGui_OnClose() {
    ExitApp
}