After a long search, this is the solution
#define UNICODE
#include once "Afx/CWindow.inc"
USING Afx
CONST IDC_POPUP = 1001
Dim Shared as Hwnd HWND_WORKSPACEMAIN
DECLARE FUNCTION WinMain (BYVAL hInstance AS HINSTANCE, _
BYVAL hPrevInstance AS HINSTANCE, _
BYVAL szCmdLine AS ZSTRING PTR, _
BYVAL nCmdShow AS LONG) AS LONG
END WinMain(GetModuleHandleW(NULL), NULL, COMMAND(), SW_NORMAL)
' // Forward declarations
DECLARE FUNCTION WndProc (BYVAL hWnd AS HWND, BYVAL uMsg AS UINT, BYVAL wParam AS WPARAM, BYVAL lParam AS LPARAM) AS LRESULT
DECLARE FUNCTION PopupWindow (BYVAL hParent AS HWND) AS CWindow PTR
DECLARE FUNCTION PopupWndProc (BYVAL hWnd AS HWND, BYVAL uMsg AS UINT, BYVAL wParam AS WPARAM, BYVAL lParam AS LPARAM) AS LRESULT
' ========================================================================================
' Main
' ========================================================================================
FUNCTION WinMain (BYVAL hInstance AS HINSTANCE, _
BYVAL hPrevInstance AS HINSTANCE, _
BYVAL szCmdLine AS ZSTRING PTR, _
BYVAL nCmdShow AS LONG) AS LONG
' // Set process DPI aware
AfxSetProcessDPIAware
' // Create the main window
DIM pWindow AS CWindow
DIM hWndMain AS HWND = pWindow.Create(NULL, "Modeless popup window", @WndProc)
pWindow.SetClientSize(900, 500)
pWindow.Center
' // Add a button without position or size (it will be resized in the WM_SIZE message).
pWindow.AddControl("Button", , IDC_POPUP, "&Popup")
' // Display the window
ShowWindow(hWndMain, nCmdShow)
UpdateWindow(hWndMain)
' // Dispatch Windows messages
DIM uMsg AS MSG, hFocusWnd AS HWND
WHILE (GetMessageW(@uMsg, NULL, 0, 0) <> FALSE)
' // Check if a popup dialog is activated and get its handle
if HWND_WORKSPACEMAIN = GetFocus() then
hFocusWnd = HWND_WORKSPACEMAIN
else
hFocusWnd = hWndMain
end if
' // Process Windows messages
IF IsDialogMessageW(hFocusWnd, @uMsg) = 0 THEN
TranslateMessage(@uMsg)
DispatchMessageW(@uMsg)
END IF
WEND
FUNCTION = uMsg.wParam
END FUNCTION
' ========================================================================================
' ========================================================================================
' Window procedure
' ========================================================================================
FUNCTION WndProc (BYVAL hwnd AS HWND, BYVAL uMsg AS UINT, BYVAL wParam AS WPARAM, BYVAL lParam AS LPARAM) AS LRESULT
SELECT CASE uMsg
CASE WM_COMMAND
' // If ESC key pressed, close the application sending an WM_CLOSE message
SELECT CASE GET_WM_COMMAND_ID(wParam, lParam)
CASE IDCANCEL
IF GET_WM_COMMAND_CMD(wParam, lParam) = BN_CLICKED THEN
SendMessageW hwnd, WM_CLOSE, 0, 0
EXIT FUNCTION
END IF
CASE IDC_POPUP
IF GET_WM_COMMAND_CMD(wParam, lParam) = BN_CLICKED THEN
PopupWindow(hwnd)
EXIT FUNCTION
END IF
END SELECT
CASE WM_SIZE
IF wParam <> SIZE_MINIMIZED THEN
' // Resize the button
DIM pWindow AS CWindow PTR = AfxCWindowPtr(hwnd)
pWindow->MoveWindow GetDlgItem(hwnd, IDC_POPUP), pWindow->ClientWidth - 140, pWindow->ClientHeight - 40, 75, 23, CTRUE
END IF
CASE WM_DESTROY
' // Quit the application
PostQuitMessage(0)
EXIT FUNCTION
END SELECT
' // Default processing of Windows messages
FUNCTION = DefWindowProcW(hWnd, uMsg, wParam, lParam)
END FUNCTION
' ========================================================================================
' Popup main window
' ========================================================================================
FUNCTION PopupWindow (BYVAL hParent AS HWND) AS CWindow PTR
DIM pWindow AS CWindow PTR = NEW CWindow
pWindow->Create(hParent, "Popup window", @PopupWndProc, 0, 0, 0, 0, _
WS_POPUPWINDOW OR WS_CAPTION OR WS_CLIPSIBLINGS OR WS_CLIPCHILDREN OR WS_THICKFRAME, _
WS_EX_CONTROLPARENT OR WS_EX_WINDOWEDGE)
pWindow->Brush = GetStockObject(WHITE_BRUSH)
pWindow->SetClientSize(700, 400)
pWindow->Center(pWindow->hWindow, hParent)
' // Display the window
ShowWindow(pWindow->hWindow, SW_NORMAL)
UpdateWindow(pWindow->hWindow)
FUNCTION = pWindow
END FUNCTION
' ========================================================================================
' ========================================================================================
' Popup window procedure
' ========================================================================================
FUNCTION PopupWndProc (BYVAL hWnd AS HWND, BYVAL uMsg AS UINT, BYVAL wParam AS WPARAM, BYVAL lParam AS LPARAM) AS LRESULT
SELECT CASE uMsg
CASE WM_COMMAND
SELECT CASE GET_WM_COMMAND_ID(wParam, lParam)
CASE IDCANCEL
' // If ESC key pressed, close the application by sending an WM_CLOSE message
IF GET_WM_COMMAND_CMD(wParam, lParam) = BN_CLICKED THEN
SendMessageW hwnd, WM_CLOSE, 0, 0
EXIT FUNCTION
END IF
END SELECT
CASE WM_DESTROY
' // Delete the popup CWindow class
DIM pWindow AS CWindow PTR = AfxCWindowPtr(hwnd)
IF pWindow THEN Delete pWindow
EXIT FUNCTION
END SELECT
' // Default processing of Windows messages
FUNCTION = DefWindowProcW(hWnd, uMsg, wParam, lParam)
END FUNCTION
' ========================================================================================
