Qt Windows 7 extend frame into client area with transparency

I wanted to have something similar to these below:


Making the window transparent did not help me much. I was getting this:

I could not get rid of the margins.

After some research I figured out, and the result can be seen below:




To get merge the margins with the window frame it is enough to call DwmExtendFrameIntoClientArea with the margins value set to -1.

void ExtendFrameIntoClientArea(QWidget* widget) {
MARGINS margins = {-1};

DwmExtendFrameIntoClientArea(widget->winId(), &margins);
}


The transparency part is easy, it was published long time ago:

long EnableBlurBehindWidget(QWidget* widget, bool enable)
{
HWND hwnd = widget->winId();
HRESULT hr = S_OK;

widget->setAttribute(Qt::WA_TranslucentBackground, enable);
widget->setAttribute(Qt::WA_NoSystemBackground, enable);

// Create and populate the Blur Behind structure
DWM_BLURBEHIND bb = {0};

bb.dwFlags = DWM_BB_ENABLE;
bb.fEnable = enable;
bb.hRgnBlur = NULL;

DwmEnableBlurBehindWindow(hwnd, &bb);
return hr;
}

I have managed to compile this using MINGW. The DwmEnableBlurBehindWindow and DwmExtendFrameIntoClientArea are loaded directly from dwmapi.dll.

#include <windows.h>

#define DWM_BB_ENABLE 0x00000001 // fEnable has been specified

typedef struct _DWM_BLURBEHIND
{
DWORD dwFlags;
BOOL fEnable;
HRGN hRgnBlur;
BOOL fTransitionOnMaximized;
} DWM_BLURBEHIND, *PDWM_BLURBEHIND;

typedef struct _MARGINS
{
int cxLeftWidth; // width of left border that retains its size
int cxRightWidth; // width of right border that retains its size
int cyTopHeight; // height of top border that retains its size
int cyBottomHeight; // height of bottom border that retains its size
} MARGINS, *PMARGINS;

extern "C"
{
typedef HRESULT (WINAPI *t_DwmEnableBlurBehindWindow)(HWND hWnd, const DWM_BLURBEHIND* pBlurBehind);
typedef HRESULT (WINAPI *t_DwmExtendFrameIntoClientArea)(HWND hwnd, const MARGINS *pMarInset);
}

void DwmExtendFrameIntoClientArea(HWND hwnd, const MARGINS *pMarInset) {
HMODULE shell;

shell = LoadLibrary(L"dwmapi.dll");
if (shell) {
t_DwmExtendFrameIntoClientArea set_window_frame_into_client_area = reinterpret_cast<t_DwmExtendFrameIntoClientArea>(GetProcAddress (shell, "DwmExtendFrameIntoClientArea"));
set_window_frame_into_client_area(hwnd, pMarInset);

FreeLibrary (shell);
}

}

void DwmEnableBlurBehindWindow(HWND hwnd, const DWM_BLURBEHIND* pBlurBehind) {
HMODULE shell;

shell = LoadLibrary(L"dwmapi.dll");
if (shell) {
t_DwmEnableBlurBehindWindow set_window_blur = reinterpret_cast<t_DwmEnableBlurBehindWindow>(GetProcAddress (shell, "DwmEnableBlurBehindWindow"));
set_window_blur(hwnd, pBlurBehind);

FreeLibrary (shell);
}
}

The project can be downloaded from here.