Is sending the message WM_GETTITLEBARINFOEX to get the caption bar RECT stable? or it has a regression?

Question

I used the following code to get the caption bar RECT to do custom NC drawings.

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif

#include <tchar.h>
#include <windows.h>
#include <uxtheme.h>
#include <vsstyle.h>
#include <dwmapi.h>

//  Declare Windows procedure
LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);

//  Make the class name into a global variable
TCHAR szClassName[] = _T("Windows App");

int WINAPI WinMain(HINSTANCE hThisInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpszArgument,
                   int nCmdShow)
{
    HWND hwnd;        // This is the handle for our window
    MSG messages;     // Here messages to the application are saved
    WNDCLASSEX wincl; // Data structure for the windowclass

    // The Window structure
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure; // This function is called by windows
    wincl.style = CS_DBLCLKS;            // Catch double-clicks
    wincl.cbSize = sizeof(WNDCLASSEX);

    // Use default icon and mouse-pointer
    wincl.hIcon = ::LoadIcon(NULL, IDI_APPLICATION);
    wincl.hIconSm = ::LoadIcon(NULL, IDI_APPLICATION);
    wincl.hCursor = ::LoadCursor(NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL; // No menu
    wincl.cbClsExtra = 0;      // No extra bytes after the window class
    wincl.cbWndExtra = 0;      // structure or the window instance
    wincl.hbrBackground = (HBRUSH)COLOR_WINDOW; // Use Windows's default color as the background of the window

    // Register the window class, and if it fails quit the program
    if (!::RegisterClassEx(&wincl))
        return 0;

    // The class is registered, let's create the program
    hwnd = ::CreateWindowEx(0,                          // Extended possibilites for variation
                            szClassName,                // Classname
                            _T("Template Windows App"), // Title Text
                            WS_OVERLAPPEDWINDOW,        // default window
                            500,                        // The window left position
                            300,                        // The window right position
                            300,                        // The programs width
                            100,                        // and height in pixels
                            HWND_DESKTOP,               // The window is a child-window to desktop
                            NULL,                       // No menu
                            hThisInstance,              // Program Instance handler
                            NULL                        // No Window Creation data
                           );

    // Make the window visible on the screen
    ::ShowWindow(hwnd, nCmdShow);

    // Run the message loop. It will run until GetMessage() returns 0
    while (::GetMessage(&messages, NULL, 0, 0))
    {
        // Translate virtual-key messages into character messages
        ::TranslateMessage(&messages);

        // Send message to WindowProcedure
        ::DispatchMessage(&messages);
    }

    // The program return-value is 0 - The value that PostQuitMessage() gave
    return messages.wParam;
}

//  This function is called by the Windows function DispatchMessage()
LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    // handle the messages
    switch (message)
    {
        case WM_NCCREATE:
        {
            DWMNCRENDERINGPOLICY ncrp = DWMNCRP_DISABLED;

            // Disable non-client area rendering on the window.
            ::DwmSetWindowAttribute(hwnd, DWMWA_NCRENDERING_POLICY, &ncrp, sizeof(ncrp));
            return TRUE;
        }

        case WM_NCACTIVATE:
        {
            return ::DefWindowProc(hwnd, message, wParam, lParam);

            //MARGINS margins = {50, 50, 50, 50};
            //::DwmExtendFrameIntoClientArea(hwnd, &margins);
            ::RedrawWindow(hwnd, NULL, NULL, RDW_UPDATENOW /*| RDW_FRAME | RDW_INVALIDATE*/);
        }

        case WM_NCPAINT:
        {
            ::DefWindowProc(hwnd, message, wParam, lParam);

//#ifndef DCX_NODELETERGN
//    #define DCX_NODELETERGN 0x00040000
//#endif

#ifndef DCX_USESTYLE
    #define DCX_USESTYLE 0x00010000
#endif

            HRGN hrgnClip;
            HRGN hrgnCaption;
            HRGN hrgnTemp;
            RECT rcMin;
            RECT rcMax;
            RECT rcClose;
            RECT rcCaption;
            RECT rcIcon;
            RECT rcWin;
            ::GetWindowRect(hwnd, &rcWin);

            if (wParam <= 1)
                hrgnTemp = ::CreateRectRgnIndirect(&rcWin);
            else
                hrgnTemp = reinterpret_cast<HRGN>(wParam);

            hrgnClip = ::CreateRectRgn(0, 0, 0, 0);
            ::CombineRgn(hrgnClip, hrgnTemp, NULL, RGN_COPY);
            HDC hdc = ::GetDCEx(hwnd, hrgnTemp, DCX_WINDOW | DCX_USESTYLE | DCX_INTERSECTRGN /*| DCX_NODELETERGN*/);

            if (!hdc)
                break;

            TITLEBARINFOEX infoex = { sizeof(infoex) };
            ::SendMessage(hwnd, WM_GETTITLEBARINFOEX, 0, (LPARAM)&infoex);
            TITLEBARINFO info = { sizeof(info) };
            ::GetTitleBarInfo(hwnd, &info);
            rcMin = infoex.rgrect[2];
            rcMax = infoex.rgrect[3];
            rcClose = infoex.rgrect[5];
            rcIcon = infoex.rcTitleBar;
            rcIcon.left = rcWin.left + ::GetSystemMetrics(SM_CXFRAME) + ::GetSystemMetrics(SM_CXPADDEDBORDER) + ::GetSystemMetrics(SM_CXEDGE);
            rcIcon.right = rcIcon.left + ::GetSystemMetrics(SM_CXSMICON);
            rcCaption = infoex.rcTitleBar;
            //rcCaption.left = rcIcon.right + ::GetSystemMetrics(SM_CXEDGE) * 2;
            rcCaption.right = rcMin.left - ::GetSystemMetrics(SM_CXEDGE) * 2;
            //rcCaption.bottom = rcCaption.top + ::GetSystemMetrics(SM_CYCAPTION);
            //rcIcon.bottom = rcCaption.bottom;

            hrgnCaption = ::CreateRectRgnIndirect(&rcCaption);
            //::ExcludeClipRect(hdc, rcCaption.left, rcCaption.top, rcCaption.right, rcCaption.bottom);
            ::CombineRgn(hrgnClip, hrgnClip, hrgnCaption, RGN_DIFF);

            HBRUSH hbRed = ::CreateSolidBrush(RGB(255, 0, 0));
            HBRUSH hbBlue = ::CreateSolidBrush(RGB(0, 0, 255));
            ::OffsetRgn(hrgnClip, -rcWin.left, -rcWin.top);
            ::OffsetRect(&rcMin, -rcWin.left, -rcWin.top);
            ::FrameRect(hdc, &rcMin, hbRed);
            ::OffsetRect(&rcMax, -rcWin.left, -rcWin.top);
            ::FrameRect(hdc, &rcMax, hbRed);
            ::OffsetRect(&rcClose, -rcWin.left, -rcWin.top);
            ::FrameRect(hdc, &rcClose, hbRed);
            ::OffsetRect(&rcCaption, -rcWin.left, -rcWin.top);
            ::FrameRect(hdc, &rcCaption, (HBRUSH)::GetStockObject(BLACK_BRUSH));
            ::OffsetRect(&rcIcon, -rcWin.left, -rcWin.top);
            ::FrameRect(hdc, &rcIcon, hbBlue);

            //RECT rcFullCaption = rcWin;
            //rcFullCaption.bottom = rcFullCaption.top + ::GetSystemMetrics(SM_CYFRAME) + ::GetSystemMetrics(SM_CXPADDEDBORDER) + ::GetSystemMetrics(SM_CYCAPTION);
            //HTHEME hTheme = ::OpenThemeData(hwnd, _T("Window"));
            //::OffsetRect(&rcFullCaption, -rcWin.left, -rcWin.top);
            //::DrawThemeBackground(hTheme, hdc, WP_CAPTION, CS_ACTIVE, &rcFullCaption, &rcIcon);
            //::CloseThemeData(hTheme);
            //::FillRect(hdc, &rcFullCaption, (HBRUSH)::GetStockObject(BLACK_BRUSH));

            //::RedrawWindow(hwnd, NULL, NULL, RDW_UPDATENOW /*| RDW_FRAME | RDW_INVALIDATE*/);
            ::DeleteObject(hrgnClip);
            ::DeleteObject(hrgnCaption);
            ::DeleteObject(hrgnTemp);

            ::DeleteObject(hbRed);
            ::DeleteObject(hbBlue);
            ::ReleaseDC(hwnd, hdc);
            break;
        }

        case WM_DESTROY:
            ::PostQuitMessage(0);    // send a WM_QUIT to the message queue
            break;

        // for messages that we don't deal with
        default:
            return ::DefWindowProc(hwnd, message, wParam, lParam);
    }

    return 0;
}

So when I called:

TITLEBARINFOEX infoex = { sizeof(infoex) };
::SendMessage(hwnd, WM_GETTITLEBARINFOEX, 0, (LPARAM)&infoex);

then used the resulting infoex.rcTitleBar I got an incorrect RECT, as illustrated in the following window capture, the rect overlapped the system icon one and is one pixel shorter in the bottom.

Here is a zoomed picture:

But, when I used the old function code instead:

TITLEBARINFO info = { sizeof(info) };
::GetTitleBarInfo(hwnd, &info);

then, everything went back to normal, as illustrated in the following window capture:

So, to get the correct title bar RECT, I either use GetTitleBarInfo() or calculate its left and bottom sides manually as follows:

rcCaption.left = rcIcon.right + ::GetSystemMetrics(SM_CXEDGE) * 2;
rcCaption.bottom = rcCaption.top + ::GetSystemMetrics(SM_CYCAPTION);

So, you can use the provided code to test it on your side and report the findings back.

TIA.

Used Windows OS: Windows 10 and Windows 11.