How to remove the borders created by DwmExtendFrameIntoClientArea?

Question

I'm creating a frameless rounded border window and calling the DwmExtendFrameIntoClientArea
API to add the shadow effect around it.

However, the API also creates a white border around the window:

These borders appear only when i call the DwmExtendFrameIntoClientArea API:

const MARGINS shadow = { 1, 1, 1, 1 };  
DwmExtendFrameIntoClientArea(mainwindow_hWnd, &shadow);  

Some things i noted:

• The borders are visible on Win10, but not on Win11.
• They are visible only when the window is focused.

Is it possible to remove or hide these borders?

Answer 1

Hi，@Leonardo
Welcome to Microsoft Q&A!
I have reproduced this scenario，

this problem occurs because of the dwStyle parameter. You must have added WS_THICKFRAME. After adding WS_POPUP, the window does not appear white border.

Could you please show a minimal, reproducible sample without private information?

Thank you.
Tong

---

If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our [documentation][2] to enable e-mail notifications if you want to receive the related email notification for this thread. [2]: https://learn.microsoft.com/en-us/answers/articles/67444/email-notifications.html

Answer 2

@Tong Xu - MSFT thank you for trying it!

Indeed adding WS_POPUP the white border doesn't appear, however the shadow is also gone and the window cant be minimized anymore.

I have been able to change that border color using the undoc SetWindowCompositionAttribute, however i couldn't get it fully transparent:

const MARGINS shadow = { 1, 1, 1, 1 };  
DwmExtendFrameIntoClientArea(mainwindow_hWnd, &shadow);  

struct ACCENTPOLICY  
{  
    int nAccentState;  
    int nFlags;  
    int nColor;  
    int nAnimationId;  
};  
struct WINCOMPATTRDATA  
{  
  int na;  
  PVOID pd;  
  ULONG ul;  
};  

/*  
typedef enum _ACCENT_STATE {  
    ACCENT_DISABLED = 0,  
    ACCENT_ENABLE_GRADIENT = 1,  
    ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,  
    ACCENT_ENABLE_BLURBEHIND = 3,  
    ACCENT_INVALID_STATE = 4  
} ACCENT_STATE;  

typedef struct _ACCENT_POLICY {  
    ACCENT_STATE AccentState;  
    DWORD        AccentFlags;  
    DWORD        GradientColor;  
    DWORD        AnimationId;  
} ACCENT_POLICY;  

_ACCENT_FLAGS{  
    DrawLeftBorder = 0x20,  
    DrawTopBorder = 0x40,  
    DrawRightBorder = 0x80,  
    DrawBottomBorder = 0x100,  
    DrawAllBorders = (DrawLeftBorder | DrawTopBorder | DrawRightBorder | DrawBottomBorder)  
}  
*/  

const HINSTANCE hm = LoadLibrary(L"user32.dll");  
if (hm)  
{  
    typedef BOOL(WINAPI* pSetWindowCompositionAttribute)(HWND, WINCOMPATTRDATA*);  

    const pSetWindowCompositionAttribute SetWindowCompositionAttribute = (pSetWindowCompositionAttribute)GetProcAddress(hm, "SetWindowCompositionAttribute");  
    if (SetWindowCompositionAttribute)  
    {  
        ACCENTPOLICY policy = { 2, 0, 0x01000000, 0 };  

        WINCOMPATTRDATA data = { 19, &policy, sizeof(ACCENTPOLICY) }; // WCA_ACCENT_POLICY=19  
        SetWindowCompositionAttribute(mainwindow_hWnd, &data);  
        DWORD err = GetLastError();  
        qDebug() << "err: " << err;  
    }  
    FreeLibrary(hm);  
}  

Could you please show a minimal, reproducible sample without private information?

I didn't share the full code because the window im working is being built using the Qt framework, I'm editing these things by handling into her DefWindowProc.

I wonder if you could share the code you've used, so i could try get it working on it and after replicate on the Qt window.

(I'm replying as an answer because i wasn't allowed to do on comment as it 'exceeded maximum characters')