Need help synchronizing MDI (WS_EX_MDICHILD) window with Child Window (WS_CHILD)

[WildByDesign]

I know that this is somewhat unusual. I also understand that MDI (WS_EX_MDICHILD) windows are intended to move with the parent GUI window, not a child window (WS_CHILD).

However, for the sake of learning and trying unusual things, here we are...

From the example, you will notice that if you move the GUI around the screen, the pink-ish square (MDI window) stays in the middle and does not move with the GUI. That is because I have associated it with the white square which is a child window (WS_CHILD).

The first part of what I want to achieve is to synchronize the movement of the MDI window with the movement of the white child window, specifically.

The second part of what I would like to achieve would be to also synchronize the sizing of MDI window.

I am still very much a rookie when it comes to WM_SIZE and WM_MOVE which I am assuming would be required here.

Anyway, if anyone has a moment and is willing to assist with this, I would appreciate it very much. Thank you.

#include <WindowsStylesConstants.au3>
#include <GUIConstantsEx.au3>

Example()

Func Example()
    ; Create a GUI with various controls.
    Local $hGUI = GUICreate("Example", 400, 400)
    GUISetBkColor(0x202020)



    ; Display the GUI.
    GUISetState(@SW_SHOW, $hGUI)

    $hChild = GUICreate("ChildWindow", 200, 200, 100, 100, 0x40000000, -1, $hGUI)
    GUISetBkColor(0xffffff)
    GUISetState(@SW_SHOW, $hChild)

    $hChildMDI = GUICreate("", 100, 100, 5, 5, $WS_POPUP, $WS_EX_MDICHILD, $hChild)
    GUISetBkColor(0xff00ff)
    GUISetState(@SW_SHOW, $hChildMDI)

    ; Loop until the user exits.
    While 1
        Switch GUIGetMsg()
            Case $GUI_EVENT_CLOSE
                ExitLoop

        EndSwitch
    WEnd

    ; Delete the previous GUI and all controls.
    GUIDelete($hGUI)
EndFunc   ;==>Example

 

[Nine]

Unless there is a specific reason to mix $WS_CHILD and $WS_EX_MDICHILD, you shouldn't do that.  All you will get out of it is useless complexity.  Now if you want to adapt the child windows to the size of its parent, here one easy way :

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; From Nine
#include <GUIConstants.au3>
#include <WindowsConstants.au3>

Opt("MustDeclareVars", True)

Global $hChild1, $hChild2, $aPosGUI

Example()

Func Example()
  Local $hGUI = GUICreate("Example", 400, 400, Default, Default, $WS_OVERLAPPEDWINDOW, $WS_EX_COMPOSITED)
  GUISetBkColor(0x202020)
  GUISetState()

  $hChild1 = GUICreate("", 200, 200, 100, 100, $WS_POPUP, $WS_EX_MDICHILD, $hGUI)
  GUISetBkColor(0xFFFFFF)
  GUISetState()

  $hChild2 = GUICreate("", 100, 100, 5, 5, $WS_POPUP, $WS_EX_MDICHILD, $hChild1)
  GUISetBkColor(0xFF00FF)
  GUISetState()

  GUIRegisterMsg($WM_SIZE, WM_SIZE)
  $aPosGUI = WinGetPos($hGUI)

  While True
    Switch GUIGetMsg()
      Case $GUI_EVENT_CLOSE
        ExitLoop
    EndSwitch
  WEnd
EndFunc   ;==>Example

Func WM_SIZE($hWnd, $iMsg, $wParam, $lParam)
  Local $aPos = WinGetPos($hWnd), $aChild1 = WinGetPos($hChild1), $aChild2 = WinGetPos($hChild2)
  WinMove($hChild1, "", $aChild1[0], $aChild1[1], $aChild1[2] + $aPos[2] - $aPosGUI[2], $aChild1[3] + $aPos[3] - $aPosGUI[3])
  WinMove($hChild2, "", $aChild2[0], $aChild2[1], $aChild2[2] + $aPos[2] - $aPosGUI[2], $aChild2[3] + $aPos[3] - $aPosGUI[3])
  $aPosGUI = $aPos
EndFunc   ;==>WM_SIZE

 

[pixelsearch]

On 11/27/2025 at 3:09 PM, WildByDesign said:

The first part of what I want to achieve is to synchronize the movement of the MDI window with the movement of the white child window, specifically.

I tried it like this, in the following script.
Please note that you can move separately the pink MDI window by dragging it with the mouse (I applied to it the "AutoIt special" Exstyle $WS_EX_CONTROLPARENT)

In this script, we don't need (for now) 2 separate functions WM_EXITSIZEMOVE() and WM_MOVE() as their content would duplicate the code found in functions WM_ENTERSIZEMOVE() and WM_SIZE() . This could change in case you'll have to work later on separate functions WM_SIZE() and WM_MOVE()

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#include <WindowsConstants.au3>
#include <GUIConstantsEx.au3>

Opt("MustDeclareVars", 1) ;0=no, 1=require pre-declaration

Global $g_hGUI, $g_hChild, $g_hChildMDI, $g_aPosChild, $g_iDeltaX, $g_iDeltaY

Example()

Func Example()
    $g_hGUI = GUICreate("Example", 400, 400, -1, -1, $WS_OVERLAPPEDWINDOW, $WS_EX_COMPOSITED)
    GUISetBkColor(0x202020)
    GUISetState(@SW_SHOW, $g_hGUI)

    $g_hChild = GUICreate("ChildWindow", 200, 200, 100, 100, $WS_CHILD, -1, $g_hGUI)
    GUISetBkColor(0xffffff)
    GUISetState(@SW_SHOW, $g_hChild)

    $g_hChildMDI = GUICreate("", 100, 100, 5, 5, $WS_POPUP, BitOr($WS_EX_MDICHILD, $WS_EX_CONTROLPARENT), $g_hChild)
    GUISetBkColor(0xff00ff)
    GUISetState(@SW_SHOW, $g_hChildMDI)

    _CalcPosAndDelta()

    GUIRegisterMsg($WM_ENTERSIZEMOVE, "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_EXITSIZEMOVE,  "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_SIZE, "WM_SIZE")
    GUIRegisterMsg($WM_MOVE, "WM_SIZE")

    While 1
        Switch GUIGetMsg()
            Case $GUI_EVENT_CLOSE
                ExitLoop
        EndSwitch
    WEnd

    GUIDelete($g_hChildMDI)
    GUIDelete($g_hChild)
    GUIDelete($g_hGUI)
EndFunc   ;==>Example

Func _CalcPosAndDelta()
    Local $aPosChildMDI = WinGetPos($g_hChildMDI)
    $g_aPosChild = WinGetPos($g_hChild)
    $g_iDeltaX = $g_aPosChild[0] - $aPosChildMDI[0]
    $g_iDeltaY = $g_aPosChild[1] - $aPosChildMDI[1]
EndFunc ;==>_CalcPosAndDelta

Func WM_ENTERSIZEMOVE($hWnd, $iMsg, $wParam, $lParam)
    _CalcPosAndDelta()
EndFunc ;==>WM_ENTERSIZEMOVE

Func WM_SIZE($hWnd, $iMsg, $wParam, $lParam)
    If $hWnd = $g_hGUI Then
        $g_aPosChild = WinGetPos($g_hChild)
        WinMove($g_hChildMDI, "", $g_aPosChild[0] - $g_iDeltaX, $g_aPosChild[1] - $g_iDeltaY)
    EndIf
EndFunc ;==>WM_SIZE

 

Edited 13 hours ago by pixelsearch
typo

[WildByDesign]

Here is a quick addition of the ListView with LVS_EX_DOUBLEBUFFER.

By the way, @pixelsearch, I see that you just edited your example. My ListView addition is based on your example that was originally posted. I still have to check your updated example.

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#include <WindowsConstants.au3>
#include <GUIConstantsEx.au3>
#include <GuiListView.au3>

; DPI
DllCall("User32.dll", "bool", "SetProcessDpiAwarenessContext" , "HWND", "DPI_AWARENESS_CONTEXT" -2)

Opt("MustDeclareVars", 1) ;0=no, 1=require pre-declaration

Global $g_hGUI, $g_hChild, $g_hChildMDI, $g_aPosChild, $g_iDeltaX, $g_iDeltaY

Example()

Func Example()
    $g_hGUI = GUICreate("Example", 400, 400, -1, -1, $WS_OVERLAPPEDWINDOW, $WS_EX_COMPOSITED)
    GUISetBkColor(0x202020)
    GUISetState(@SW_SHOW, $g_hGUI)

    $g_hChild = GUICreate("ChildWindow", 320, 320, 40, 40, 0x40000000, -1, $g_hGUI)
    GUISetBkColor(0x606060)
    GUISetState(@SW_SHOW, $g_hChild)

    $g_hChildMDI = GUICreate("", 280, 280, 20, 20, $WS_POPUP, BitOr($WS_EX_MDICHILD, $WS_EX_CONTROLPARENT), $g_hChild)
    GUISetBkColor(0xff00ff)

    ; add listview
    Local $idListview = GUICtrlCreateListView("Column1|Column2", 20, 20, 240, 240, -1, BitOR($LVS_EX_FULLROWSELECT, $WS_EX_CLIENTEDGE, $LVS_EX_DOUBLEBUFFER, $LVS_EX_CHECKBOXES))
    Local $idLVi_Item1 = GUICtrlCreateListViewItem("1|1", $idListview)
    Local $idLVi_Item2 = GUICtrlCreateListViewItem("2|2", $idListview)
    Local $idLVi_Item3 = GUICtrlCreateListViewItem("3|3", $idListview)

    ; get rid of selection rectangle on listview
    GUICtrlSendMsg($idListview, $WM_CHANGEUISTATE, 65537, 0)

    GUISetState(@SW_SHOW, $g_hChildMDI)

    _CalcPosAndDelta()

    GUIRegisterMsg($WM_ENTERSIZEMOVE, "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_EXITSIZEMOVE,  "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_SIZE, "WM_SIZE")
    GUIRegisterMsg($WM_MOVE, "WM_SIZE")

    While 1
        Switch GUIGetMsg()
            Case $GUI_EVENT_CLOSE
                ExitLoop
        EndSwitch
    WEnd

    GUIDelete($g_hChildMDI)
    GUIDelete($g_hChild)
    GUIDelete($g_hGUI)
EndFunc   ;==>Example

Func _CalcPosAndDelta()
    Local $aPosChildMDI = WinGetPos($g_hChildMDI)
    $g_aPosChild = WinGetPos($g_hChild)
    $g_iDeltaX = $g_aPosChild[0] - $aPosChildMDI[0]
    $g_iDeltaY = $g_aPosChild[1] - $aPosChildMDI[1]
EndFunc ;==>_CalcPosAndDelta

Func WM_ENTERSIZEMOVE($hWnd, $iMsg, $wParam, $lParam)
    _CalcPosAndDelta()
EndFunc ;==>WM_ENTERSIZEMOVE

Func WM_SIZE($hWnd, $iMsg, $wParam, $lParam)
    If $hWnd = $g_hGUI Then
        $g_aPosChild = WinGetPos($g_hChild)
        WinMove($g_hChildMDI, "", $g_aPosChild[0] - $g_iDeltaX, $g_aPosChild[1] - $g_iDeltaY)
    EndIf
EndFunc ;==>WM_SIZE

 

[pixelsearch]

47 minutes ago, WildByDesign said:

I see that you just edited your example.

No big deal, I simply replaced the constant 0x40000000 with its more comprehensive variable name $WS_CHILD, no more no less

As you can see in my script, it's very easy to synchronize a MDI (WS_EX_MDICHILD) window with a Child Window (WS_CHILD) . It also works if you minimize / maximize / restore the GUI.

I like the fact that the 2 registered functions WM_ENTERSIZEMOVE and WM_EXITSIZEMOVE are called only 1 time per moving/sizing loop (I added a counter during tests and it's true). This is what MSDN stipulates about them :

WM_ENTERSIZEMOVE : Sent one time to a window after it enters the moving or sizing modal loop
WM_EXITSIZEMOVE  : Sent one time to a window, after it has exited the moving or sizing modal loop.

So they are "light" messages that don't require a lot of CPU at all and you can (re)initialize variables inside the functions, very useful !

According to trancexx at the very end of an old interesting thread... wait, let me paste the post and the link to the thread :

On 3/25/2010 at 8:10 AM, trancexx said:

On 3/25/2010 at 7:48 AM, 'martin said:

I notice there is a listview extended style $LVS_EX_DOUBLEBUFFER which I thought might be a better solution than using $WS_EX_COMPOSITED for the window. I tried it but it doesn't reduce the flicker for me.

 

It's not supposed to. That style reduces flicker when you resize columns, not the whole listview.

 

Edited 13 hours ago by pixelsearch
typo

[pixelsearch]

@WildByDesign great result with the listview inside the MDI window

So $WS_EX_COMPOSITED is now applied to the GUI (less flicker when resizing the GUI) and doesn't interfere with the "$LVS_EX_DOUBLEBUFFER listview" which is a control of an external MDI window, bravo !

[WildByDesign]

16 minutes ago, pixelsearch said:

I like the fact that the 2 registered functions WM_ENTERSIZEMOVE and WM_EXITSIZEMOVE are called only 1 time per moving/sizing loop (I added a counter during tests and it's true). This is what MSDN stipulates about them :

That is fantastic. Very efficient. By the way, this is all really quite genius.

17 minutes ago, pixelsearch said:

According to trancexx at the very end of an old interesting thread... wait, let me paste the post and the link to the thread :

What a coincidence, I was actually reading this same thread earlier in the morning. Sometimes I spend a good amount of time reading older threads here in the forum because it's literally a gold mine worth of information.

Anyways, your technique is working. I've got it working with WS_EX_COMPOSITE and a perfectly working ListView thanks to the MDI GUI trick.

I'll post the screenshot and more details in another comment because I just ran out of quota again...

[WildByDesign]

This is what I have working so far. I'll have to open up a thread soon so that anyone can help if they want. I've got lots of ideas already for adding menubar, toolbar, statusbar, etc.

The only thing that I need to figure out still is resizing the MDI GUI when the child GUI resizes.

 

[pixelsearch]

11 hours ago, WildByDesign said:

The only thing that I need to figure out still is resizing the MDI GUI when the child GUI resizes.

Fingers crossed

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#include <WindowsConstants.au3>
#include <GUIConstantsEx.au3>
#include <GuiListView.au3>

; DPI
DllCall("User32.dll", "bool", "SetProcessDpiAwarenessContext" , "HWND", "DPI_AWARENESS_CONTEXT" -2)

Opt("MustDeclareVars", 1) ;0=no, 1=require pre-declaration

Global $g_hGUI, $g_hChild, $g_hChildMDI, $g_aPosChild, $g_aDelta[4], $g_nRatio[4]

Example()

Func Example()
    Local $iParentW = 400, $iParentH = 400
    Local $iChildW = 320, $iChildH = 320, $iChildX = 40, $iChildY = 40

    $g_hGUI = GUICreate("Example", $iParentW, $iParentH, -1, -1, $WS_OVERLAPPEDWINDOW, $WS_EX_COMPOSITED)
    GUISetBkColor(0x202020)
    GUISetState(@SW_SHOW, $g_hGUI)

    $g_hChild = GUICreate("ChildWindow", $iChildW, $iChildH, $iChildX, $iChildY, $WS_CHILD, -1, $g_hGUI)
    GUISetBkColor(0x606060)
    Local $idLabel = GUICtrlCreateLabel("", 0, 0, $iChildW, $iChildH)
    GUICtrlSetState(-1, $GUI_DISABLE)
    GUISetState(@SW_SHOW, $g_hChild)

    $g_hChildMDI = GUICreate("", 280, 280, 20, 20, $WS_POPUP, BitOr($WS_EX_MDICHILD, $WS_EX_CONTROLPARENT), $g_hChild)
    GUISetBkColor(0xff00ff)
    ; add listview
    Local $idListview = GUICtrlCreateListView("Column1|Column2", 20, 20, 240, 240, -1, BitOR($LVS_EX_FULLROWSELECT, $WS_EX_CLIENTEDGE, $LVS_EX_DOUBLEBUFFER, $LVS_EX_CHECKBOXES))
    Local $idLVi_Item1 = GUICtrlCreateListViewItem("1|1", $idListview)
    Local $idLVi_Item2 = GUICtrlCreateListViewItem("2|2", $idListview)
    Local $idLVi_Item3 = GUICtrlCreateListViewItem("3|3", $idListview)
    ; get rid of selection rectangle on listview
    GUICtrlSendMsg($idListview, $WM_CHANGEUISTATE, 65537, 0)
    GUISetState(@SW_SHOW, $g_hChildMDI)

    $g_nRatio[0] = $iChildX / $iParentW
    $g_nRatio[1] = $iChildY / $iParentH
    $g_nRatio[2] = $iChildW / $iParentW
    $g_nRatio[3] = $iChildH / $iParentH

    _CalcPosAndDelta()

    GUIRegisterMsg($WM_ENTERSIZEMOVE, "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_EXITSIZEMOVE,  "WM_ENTERSIZEMOVE")
    GUIRegisterMsg($WM_SIZE, "WM_SIZE")
    GUIRegisterMsg($WM_MOVE, "WM_MOVE")

    While 1
        Switch GUIGetMsg()
            Case $GUI_EVENT_CLOSE
                ExitLoop
        EndSwitch
    WEnd

    GUIDelete($g_hChildMDI)
    GUIDelete($g_hChild)
    GUIDelete($g_hGUI)
EndFunc   ;==>Example

Func _CalcPosAndDelta()
    Local $aPosChildMDI = WinGetPos($g_hChildMDI)
    $g_aPosChild = WinGetPos($g_hChild)
    For $i = 0 To 3
        $g_aDelta[$i] = $g_aPosChild[$i] - $aPosChildMDI[$i]
    Next
EndFunc ;==>_CalcPosAndDelta

Func WM_ENTERSIZEMOVE($hWnd, $iMsg, $wParam, $lParam)
    _CalcPosAndDelta()
EndFunc ;==>WM_ENTERSIZEMOVE

Func WM_SIZE($hWnd, $iMsg, $wParam, $lParam)
    If $hWnd = $g_hGUI Then
        Local $iParentNewCliW = BitAND($lParam, 0xFFFF) ; low word
        Local $iParentNewCliH = BitShift($lParam, 16) ; high word
        WinMove($g_hChild, "", $iParentNewCliW * $g_nRatio[0], $iParentNewCliH * $g_nRatio[1], _
            $iParentNewCliW * $g_nRatio[2], $iParentNewCliH * $g_nRatio[3]) ; WinMove will use Int coords

        $g_aPosChild = WinGetPos($g_hChild)
        WinMove($g_hChildMDI, "", $g_aPosChild[0] - $g_aDelta[0], $g_aPosChild[1] - $g_aDelta[1] , _
            $g_aPosChild[2] - $g_aDelta[2], $g_aPosChild[3] - $g_aDelta[3])
    EndIf
EndFunc ;==>WM_SIZE

Func WM_MOVE($hWnd, $iMsg, $wParam, $lParam)
    If $hWnd = $g_hGUI Then
        $g_aPosChild = WinGetPos($g_hChild)
        WinMove($g_hChildMDI, "", $g_aPosChild[0] - $g_aDelta[0], $g_aPosChild[1] - $g_aDelta[1])
    EndIf
EndFunc ;==>WM_MOVE

 

[WildByDesign]

19 minutes ago, pixelsearch said:

Fingers crossed

This is absolute perfection! Thank you so much. 🍷

I know it may seem like a lot of "extra" here, for anyone else that may be following along or reading later. I really enjoy smooth GUI movement (flicker-free) with WS_EX_COMPOSITED, particularly combined with the GUIFrame UDF in this case. But at the same time, I am a huge fan of ListViews and use many of them in most of my bigger projects. I love ListViews. So this MDI window trick was a blessing.