Why does getwindowrect and getmenubarinfo both return wrong values?

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I am at the moment handling the WM_NCPAINT for my app. I painted a section of the top non-client area using the return value of GetWindowRect but the coordinates fell inside my applications client area. I decided to Use GetMenuBarInfo to get the menubar coordinates but the experience was the same. Using the update region made avilable by wParam is about the same result. How can I remedy these?

The relevant codes are shown below.

In the codes below, I expect GetWindowRect to return the coordinates of the window in question such that when I replace the RECT.bottom value of the returned value by 100, a band of colour starting from the top of the window and down until 100 pixels below is reached is drawn. I do not expect the band of colour to fall within the client rect not to talk of starting in it, but what I see is a displaced colour band stating at a distance in the client rect,

C++

 hdc = GetWindowDC(hWnd);
 HBRUSH hBrush = CreateSolidBrush(AppColor);
 RECT rcWindow;
 GetWindowRect(hWnd,&rcWindow);
 rcWindow.bottom = 100;
 RECT rcFill{ rcWindow };

 FillRect(hdc, &rcFill, hBrush);
 DeleteObject(hBrush);

ReleaseDC(hWnd,hdc);

In the code below, I expect the menu bar to be filled with the specified colour, but what I get is a band of colour equal in size to the menu bar but displaced insde the client region.

C++

hdc = GetWindowDC(hWnd);
MENUBARINFO menuInfo = { sizeof(MENUBARINFO) };
if (GetMenuBarInfo(hWnd, OBJID_MENU, 0, &menuInfo))
{
    HBRUSH hBrush = CreateSolidBrush(AppColor);
    RECT rcFill{ menuInfo.rcBar };

    FillRect(hdc, &rcFill, hBrush);
    DeleteObject(hBrush);
}
ReleaseDC(hWnd,hdc);

In the code below, I expect the entire window non-client area to be filled with a specified colour. Instead what I see is a band of area with size identical to the window frame but displaced from the window frame filled with the specified colour.

C++

HDC hdc = GetWindowDC(hWnd);

HBRUSH hBrush = CreateSolidBrush(AppColor);
HRGN hFillRgn = (HRGN)wParam;
if (!FillRgn(hdc, hFillRgn, hBrush))

{
    long lErrorCode = GetLastError();
    GetErrorMessageBox(lErrorCode);
}
DeleteObject(hBrush);

ReleaseDC(hWnd,hdc);

What I have tried:

I have read documentation on the two functions. It did not help.

Posted 12-Jul-24 15:01pm

Gbenbam

Updated 13-Jul-24 6:39am

v5

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merano99 · Answer 1 · 2024-07-14T21:11:00

If I understand it correctly, the menu bar of a Win32 program written in C++ is to be painted over with a rectangle for testing by using the WM_NCPAINT message. It works with a test program under Windows 10. The relevant code for WM_NCPAINT in the window procedure to color the entire area of the menu bar and the area directly below it could look like this:

C++

case WM_NCPAINT: {
    RECT windowRect, menuRect;
    HDC hdc = GetWindowDC(hWnd);
    GetWindowRect(hWnd, &windowRect);
    OffsetRect(&windowRect, -windowRect.left, -windowRect.top);
    DefWindowProc(hWnd, WM_NCPAINT, wParam, lParam);
    HMENU hMenu = GetMenu(hWnd);
    if (hMenu) {
        int menuHeight = GetSystemMetrics(SM_CYMENU);
        int frameHeight = GetSystemMetrics(SM_CYFRAME);
        int captionHeight = GetSystemMetrics(SM_CYCAPTION);

        menuRect.top = captionHeight + frameHeight;
        menuRect.bottom = menuRect.top + menuHeight + frameHeight;
        menuRect.left = windowRect.left;
        menuRect.right = windowRect.right;

        HBRUSH brush = CreateSolidBrush(RGB(255, 0, 0));  // Rote Farbe
        FillRect(hdc, &menuRect, brush);
        DeleteObject(brush);
    }
    ReleaseDC(hWnd, hdc);
    return 0;
}

Richard MacCutchan · Answer 2 · 2024-07-13T02:07:00

Solution 1

The MSDN documentation at WM_NCPAINT message (Winuser.h) - Win32 apps | Microsoft Learn[^] explains (and provides sample code) that the message provides a handle to the actual update region that needs to be painted.

Posted 13-Jul-24 2:07am

Richard MacCutchan

Comments

Gbenbam 13-Jul-24 8:35am

So, can you help with sample code on how to paint the menu bar? Is the menu bar part of the windows frame? I thought WM_NCPAINT is for repainting the non-client region. The term "window frame" is it the same as the non-client region?

Richard MacCutchan 13-Jul-24 9:16am

I have tried a number of tests and it seems that the WM_NCPAINT message does not send a valid region handle with it. I guess this is either a bug in the Windows library, or the documentation is not up to date.

Gbenbam 13-Jul-24 10:03am

The documentation is dated 01/07/202101. It is reasonably up to date? Perhaps, your interpretation of the documentation is incorrect. My own interpretation is that the documentation was this: get a dc to the region to update and then draw whaterver you wish to draw in the region bearing in mind that drawing outside the region will be clipped. That is what the example code of WM_NCPAINT seem to suggest.

Richard MacCutchan 13-Jul-24 10:09am

Well that has nothing to do with the actual issue. If you use your debugger and step through the code you can clearly see that the WPARAM value is not a handle (it is the integer 1). Also a call to FillRgn returns zero, which means the call failed. So you can deduce from that that either the documentation is not up to date, or the system has a bug. So your best bet is to report this to Microsoft.

Gbenbam 13-Jul-24 10:13am

Can you help to report it to Microsoft?

Richard MacCutchan 13-Jul-24 10:28am

This is your issue so you need to report it. Just create a simple code sample and post it with your explanation on the appropriate Microsoft forum.

Gbenbam 13-Jul-24 11:11am

Even though FillRect succeeded, the painted region is displaced. It does not fit to the expected location of the window frame.

Gbenbam 13-Jul-24 11:15am

This brings us back to the original issue. GetWindowRect gave incorrect location, GetMenubarInfo gave incorrect location wParam of WM_NCPAINT gave incorrect region. Why? Why? Why?

Richard MacCutchan 13-Jul-24 11:34am

It is no good just saying everything is wrong. Show the code you are using, explain what results you expect, and what you actually get, and why you think they are wrong.

Gbenbam 13-Jul-24 12:06pm

Ok. I will update with code and explanation of intent, expected outcome and actual outcome.

Gbenbam 13-Jul-24 12:43pm

I have updated the question kindly have another look at it.

Gbenbam 13-Jul-24 11:01am

For your information, the region is very much valid. When I used GetWindowDC to get a device concept. FillRegn succeeded.

Richard MacCutchan 13-Jul-24 11:26am

Fine, but that is not the issue that you reported.

Gbenbam 13-Jul-24 13:10pm

I believe the reason why FillRgn failed when a dc was gotten with GetDCEx is because, according to documentation, even though the upate region is a recangle, the client area part of is s clipped to remain the window frame when a device context is gotten with GetDCEx. So, FillRgn failed because the device context was not valid for that operation. FillRgn does not fill an exterior part of a rectangle with a seeming rectangular hole, in short FillRgn is not the appropriate function for that operation if GetDCEx is used.

Richard MacCutchan 13-Jul-24 13:13pm

As I explained earlier, the reason it fails is because wParam does not contain a valid region handle. So GetDCEx fails to return a valid DC, and FillRgn fails because both the DC and the region are invalid.

Gbenbam 13-Jul-24 13:42pm

But the code below succeeded:

HDC hdc = GetWindowDC(hWnd);
HRGN hFillRgn = (HRGN)wParam;
HBRUSH hBrush = CreateSolidBrush((COLORREF(RGB(255,215,0)));
FillRgn(hdc,hFillRgn,hBrush);
DeleteObject(hBrush);

Not only did it succeed code-run-wise, I visually saw the sucess on the screen albeit with some inproper dispacing. So, yes wParam contains a vald region.

Richard MacCutchan 14-Jul-24 8:28am

As far as I can tell, the region values are all offset by some fixed value. If you adjust them by subtracting the top and left values from each point in each RECT structure of the data returned from a call to GetRegionData, then you may be able to get a region the corresponds to the Window's actual frame. It just seems far too much work for something not that critical to any application.

Gbenbam 14-Jul-24 18:32pm

I'll do exactly that. It makes it possible for my application to have a different colour. Or do you know any other way I can customize my application to have a different colour and possibly more customization?

Richard MacCutchan 15-Jul-24 3:42am

If you want comlete customisation then you can use Windows skinning to create your own coloured and shaped Window. There are many articles on the subject, but one I have used in the past is flipcode - Win32 Window Skinning[^].

Gbenbam 15-Jul-24 13:43pm

My actual intention is to change the colour of the non-client area to match the colour of my dialog boxes. I already have a funtioning owner drawn menu. What do you suggest?

Richard MacCutchan 16-Jul-24 4:25am

I do not have any more suggestions. As far as my tests went, there is more to handling the WM_NCPAINT message(s) than just capturing the message and using the region parameter. As I suggested yesterday you may find that the skinning option is easier.

Gbenbam 17-Jul-24 14:15pm

Can you possibly help with a sample code for skinning the non-vacant area of non client region. By non- vacant I mean the Icon, the Window Title, the maximize, minimize, restore button, the close buttons,the part o the menu bar that has a content and the scroll bars.

Richard MacCutchan 18-Jul-24 4:24am

I'm sorry no. I have given you what information I know about, it is up to you to try it and decide whether it solves your problem.

Gbenbam 13-Jul-24 9:14am

HBRUSH hBrush = CreateSolidBrush(COLORREF(RGB(255,215,0)));
HRGN hFillRgn = (HRGN)wParam;
FillRgn(hdc, hFillRgn, hBrush);
DeleteObject(hBrush);

I did the above and got absolutely no result. Why?

Uwe Klatt · Answer 3 · 2024-08-05T01:42:00

The following code works for me, if there is an existing menu:

C++

case WM_NCPAINT:
     HDC hdc = GetWindowDC( hWnd );
     MENUBARINFO menuInfo = {sizeof( MENUBARINFO )};
     if ( GetMenuBarInfo( hWnd, OBJID_MENU, 0L, &menuInfo ) )
     {
       HBRUSH hBrush = CreateSolidBrush( RGB(255,128,128) );
       RECT rcFill = menuInfo.rcBar;

       FillRect( hdc, &rcFill, hBrush );
       DeleteObject( hBrush );
     }
     ReleaseDC( hWnd, hdc );
     return 0;

C++

RECT rcFill = {menuInfo.rcBar};

Seems to be wrong.

Uwe

Why does getwindowrect and getmenubarinfo both return wrong values?

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