Qt/Windows, resizable frameless window - c++

Question

I need to create a frameless Qt Windows app that supports resizing.
If I use
setWindowFlags(Qt::FramelessWindowHint);
then I can resize only from bottom-right corner (like with the size grip, I guess QMainWindow includes it somehow?).
Is there any easy way to make it resizable from all sides like a normal window? Maybe something platform-specific (Windows)?

Answer 1

Solved it using WM_NCHITTEST, based on code from https://bugreports.qt.io/browse/QTBUG-40578 (bug report not related to this).
.h
class MainWindow : public QMainWindow
{
Q_OBJECT
......
protected:
bool nativeEvent(const QByteArray& eventType, void* message, long* result) override;
};
.cpp
bool MainWindow::nativeEvent(const QByteArray& eventType, void* message, long* result)
{
MSG* msg = static_cast<MSG*>(message);
if (msg->message == WM_NCHITTEST)
{
if (isMaximized())
{
return false;
}
*result = 0;
const LONG borderWidth = 8;
RECT winrect;
GetWindowRect(reinterpret_cast<HWND>(winId()), &winrect);
// must be short to correctly work with multiple monitors (negative coordinates)
short x = msg->lParam & 0x0000FFFF;
short y = (msg->lParam & 0xFFFF0000) >> 16;
bool resizeWidth = minimumWidth() != maximumWidth();
bool resizeHeight = minimumHeight() != maximumHeight();
if (resizeWidth)
{
//left border
if (x >= winrect.left && x < winrect.left + borderWidth)
{
*result = HTLEFT;
}
//right border
if (x < winrect.right && x >= winrect.right - borderWidth)
{
*result = HTRIGHT;
}
}
if (resizeHeight)
{
//bottom border
if (y < winrect.bottom && y >= winrect.bottom - borderWidth)
{
*result = HTBOTTOM;
}
//top border
if (y >= winrect.top && y < winrect.top + borderWidth)
{
*result = HTTOP;
}
}
if (resizeWidth && resizeHeight)
{
//bottom left corner
if (x >= winrect.left && x < winrect.left + borderWidth &&
y < winrect.bottom && y >= winrect.bottom - borderWidth)
{
*result = HTBOTTOMLEFT;
}
//bottom right corner
if (x < winrect.right && x >= winrect.right - borderWidth &&
y < winrect.bottom && y >= winrect.bottom - borderWidth)
{
*result = HTBOTTOMRIGHT;
}
//top left corner
if (x >= winrect.left && x < winrect.left + borderWidth &&
y >= winrect.top && y < winrect.top + borderWidth)
{
*result = HTTOPLEFT;
}
//top right corner
if (x < winrect.right && x >= winrect.right - borderWidth &&
y >= winrect.top && y < winrect.top + borderWidth)
{
*result = HTTOPRIGHT;
}
}
if (*result != 0)
return true;
QWidget *action = QApplication::widgetAt(QCursor::pos());
if (action == this){
*result = HTCAPTION;
return true;
}
}
return false;
}
implementation from Qt: Resize borderless widget did not work well: sometimes the window is moved during resizing (even in the first version without dragging)