Window Title Bar Appears Transparent Issue (Not Really Transparent)

Window title bar appears transparent issue (Not really transparent)

Try add:

self.window?.styleMask |= NSFullSizeContentViewWindowMask

When set, the content view consumes the full size of the window; it
can be combined with other window style masks, but is only respected
for windows with a title bar. Using this mask opts in to layer
backing. Use the contentLayoutRect or contentLayoutGuide to lay out
views underneath the title bar-toolbar area

If you don't want to keep the title bar at all, you can also added:

self.window?.titleVisibility = NSWindowTitleVisibility.Hidden;

The window hides the title and moves the toolbar up into the area
previously occupied by the title.

You might also wanted to add this in order to move the window by dragging its content view:

self.window?.movableByWindowBackground = YES

A Boolean value that indicates whether the window is movable by
clicking and dragging anywhere in its background. The value of this
property is YES when the window is movable by clicking and dragging
anywhere in its background; otherwise, NO.

Transparent title bar in WinUI 3 app (Windows 11)

According to the Doc:

If you set ExtendsContentIntoTitleBar to true but do not call
SetTitleBar, the system title bar is restricted to the caption
buttons and a small area next to the caption buttons that is reserved
for title bar behaviors. However, your custom title bar element does
not get title bar behaviors, such as drag and the system menu, until
SetTitleBar is called with a valid UIElement.

Set the transparency by setting the value of UIElement.Opacity Property:

The value between 0 and 1.0 that declares the opacity factor, with 1.0 meaning full opacity and 0 meaning transparent. The default value is 1.0.

Window not movable with full size content view in combination with transparent title bar

Most probably your view is opaque, because NSWindow.isMovableByWindowBackground indicates that window can be moved by own background.

In such case you have to subclass used NSxxxxView and override NSView.mouseDownCanMoveWindow read-only property to return true.

Win32 Prevent being transparent the borders of the Window

It looks like you want to make part of the window transparent.For this, you need to create two windows to complete.

Use SetWindowRgn to create a window with a hole
Use the WS_EX_LAYERED and WS_EX_TRANSPARENT style to place
another transparent window in the hole.

Like this:

Sample Image

The whole code:

// Test_transparent.cpp : Defines the entry point for the application.
//

#include "framework.h"
#include "Test_transparent.h"

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;                                // current instance
WCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name

// Forward declarations of functions included in this code module:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);
HWND hWnd;
HWND child;

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // TODO: Place code here.

    // Initialize global strings
    LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadStringW(hInstance, IDC_TESTTRANSPARENT, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // Perform application initialization:
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_TESTTRANSPARENT));

    MSG msg;

    // Main message loop:
    while (GetMessage(&msg, nullptr, 0, 0))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}

//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEXW wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);

    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_TESTTRANSPARENT));
    wcex.hCursor        = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = MAKEINTRESOURCEW(IDC_TESTTRANSPARENT);
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    return RegisterClassExW(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   hWnd = CreateWindowEx(0, szWindowClass, L" ", WS_POPUP, 100, 100, 800, 600, NULL, NULL, hInst, 0);
   child = CreateWindowEx(WS_EX_LAYERED, szWindowClass, szTitle, WS_POPUP | WS_VISIBLE | WS_CHILD, 300, 300, 200, 200, hWnd, NULL, hInst, 0);
   SetLayeredWindowAttributes(child, 0, 50, LWA_ALPHA);

   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE: Processes messages for the main window.
//
//  WM_COMMAND  - process the application menu
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    RECT rect;
    RECT rc;
    COLORREF    brColor;
    static HRGN     hRgnWnd;
    static HRGN     hRgnWnd1;
    static HBRUSH   hBr;
    switch (message)
    {       
    case WM_COMMAND:
        {
            int wmId = LOWORD(wParam);
            // Parse the menu selections:
            switch (wmId)
            {
            case IDM_ABOUT:
                DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
                break;
            case IDM_EXIT:
                DestroyWindow(hWnd);
                break;
            default:
                return DefWindowProc(hWnd, message, wParam, lParam);
            }
        }
        break;

    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);
            // TODO: Add any drawing code that uses hdc here...           
            brColor = RGB(51, 143, 178);
            hBr = CreateSolidBrush(brColor);     
            GetClientRect(hWnd, &rect);
            rc.left = 200;
            rc.top = 200;
            rc.right = 400;
            rc.bottom = 400;
            hRgnWnd = CreateRectRgn(rect.left, rect.top, rect.right, rect.bottom);
            hRgnWnd1 = CreateRectRgn(rc.left, rc.top, rc.right, rc.bottom);
            CombineRgn(hRgnWnd1, hRgnWnd1, hRgnWnd, RGN_XOR);
            SetWindowRgn(hWnd, hRgnWnd1, true);
            FillRect(hdc, &rect, hBr);

            EndPaint(hWnd, &ps);
        }
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    }
    return (INT_PTR)FALSE;
}

To get a borderless window, you need to comment the MENU code in the .rc file.

.rc cpp

//Microsoft Visual C++ generated resource script.
//
#include "resource.h"

#define APSTUDIO_READONLY_SYMBOLS
/////////////////////////////////////////////////////////////////////////////
//
// Generated from the TEXTINCLUDE resource.
//
#ifndef APSTUDIO_INVOKED
#include "targetver.h"
#endif
#define APSTUDIO_HIDDEN_SYMBOLS
#include "windows.h"
#undef APSTUDIO_HIDDEN_SYMBOLS
/////////////////////////////////////////////////////////////////////////////
#undef APSTUDIO_READONLY_SYMBOLS

#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)
LANGUAGE 9, 1

/////////////////////////////////////////////////////////////////////////////
//
// Icon
//

// Icon with lowest ID value placed first to ensure application icon
// remains consistent on all systems.

IDI_TESTTRANSPARENT       ICON         "Test_transparent.ico"
IDI_SMALL               ICON         "small.ico"

/////////////////////////////////////////////////////////////////////////////
//
// Menu
//
//
//IDC_TESTTRANSPARENT MENU
//BEGIN
//    POPUP "&File"
//    BEGIN
//        MENUITEM "E&xit",                IDM_EXIT
//    END
//    POPUP "&Help"
//    BEGIN
//        MENUITEM "&About ...",           IDM_ABOUT
//    END
//END

/////////////////////////////////////////////////////////////////////////////
//
// Accelerator
//

IDC_TESTTRANSPARENT ACCELERATORS
BEGIN
    "?",            IDM_ABOUT,              ASCII,  ALT
    "/",            IDM_ABOUT,              ASCII,  ALT
END

/////////////////////////////////////////////////////////////////////////////
//
// Dialog
//

IDD_ABOUTBOX DIALOGEX 0, 0, 170, 62
STYLE DS_SETFONT | DS_MODALFRAME | DS_FIXEDSYS | WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "About Test_transparent"
FONT 8, "MS Shell Dlg"
BEGIN
    ICON            IDR_MAINFRAME,IDC_STATIC,14,14,21,20
    LTEXT           "Test_transparent, Version 1.0",IDC_STATIC,42,14,114,8,SS_NOPREFIX
    LTEXT           "Copyright (c) 2020",IDC_STATIC,42,26,114,8
    DEFPUSHBUTTON   "OK",IDOK,113,41,50,14,WS_GROUP
END

/////////////////////////////////////////////////////////////////////////////
//
// DESIGNINFO
//

#ifdef APSTUDIO_INVOKED
GUIDELINES DESIGNINFO
BEGIN
    IDD_ABOUTBOX, DIALOG
    BEGIN
        LEFTMARGIN, 7
        RIGHTMARGIN, 163
        TOPMARGIN, 7
        BOTTOMMARGIN, 55
    END
END
#endif    // APSTUDIO_INVOKED

#ifdef APSTUDIO_INVOKED
/////////////////////////////////////////////////////////////////////////////
//
// TEXTINCLUDE
//
1 TEXTINCLUDE
BEGIN
    "resource.h\0"
END

2 TEXTINCLUDE
BEGIN
    "#ifndef APSTUDIO_INVOKED\r\n"
    "#include ""targetver.h""\r\n"
    "#endif\r\n"
    "#define APSTUDIO_HIDDEN_SYMBOLS\r\n"
    "#include ""windows.h""\r\n"
    "#undef APSTUDIO_HIDDEN_SYMBOLS\r\n"
    "\0"
END

3 TEXTINCLUDE
BEGIN
    "\r\n"
    "\0"
END

#endif    // APSTUDIO_INVOKED

/////////////////////////////////////////////////////////////////////////////
//
// String Table
//

STRINGTABLE
BEGIN
   IDC_TESTTRANSPARENT   "TESTTRANSPARENT"
   IDS_APP_TITLE       "Test_transparent"
END

#endif
/////////////////////////////////////////////////////////////////////////////

#ifndef APSTUDIO_INVOKED
/////////////////////////////////////////////////////////////////////////////
//
// Generated from the TEXTINCLUDE resource.
//

/////////////////////////////////////////////////////////////////////////////
#endif    // not APSTUDIO_INVOKED

Window Title Bar Appears Transparent Issue (Not Really Transparent)