Shadow for qml frameless windows - qt

Question

I have frameless main window, created by qml ( ApplicationWindow {..} in my main.qml file)
I instantiate qml by QQmlApplicationEngine::load (class introduced in Qt5.1).
If I set the Qt.FramelessWindowHint flag, the window is frameless, but loses shadow (in Windows).
How to add shadow to my window?
My window listing:
ApplicationWindow {
id: rootWindow
color : "#f8f8f8"
maximumHeight: 445
minimumHeight: 445
minimumWidth: 730
maximumWidth: 730
flags : Qt.FramelessWindowHint | Qt.Window
Component.onCompleted: {
setHeight(455)
setWidth(740)
}
MainObject{
id:mainObject1
anchors.fill: parent
height:445
width:730
}
}

Answer 1

The solution is to implement the shadow part integral to the application, this way you can disable WM decoration and still have decoration, and have it consistent across different platforms.
In the following example the window has a shadow that even animates to create the effect of lifting the window up when moving it. And when the window is maximized, the margins are removed and the shadow is thus no longer visible.
import QtQuick 2.7
import QtQuick.Controls 2.1
import QtGraphicalEffects 1.0
import QtQuick.Window 2.3
ApplicationWindow {
id: main
visible: true
width: 300
height: 200
color: "#00000000"
flags: Qt.FramelessWindowHint | Qt.Window
Rectangle {
id: rect
anchors.fill: parent
anchors.margins: main.visibility === Window.FullScreen ? 0 : 10
MouseArea {
id: ma
anchors.fill: parent
property int dx
property int dy
onPressed: { dx = mouseX; dy = mouseY }
onPositionChanged: {
main.x += mouseX - dx
main.y += mouseY - dy
}
onDoubleClicked: main.visibility = main.visibility === Window.FullScreen ? Window.AutomaticVisibility : Window.FullScreen
}
}
DropShadow {
anchors.fill: rect
horizontalOffset: 1
verticalOffset: 1
radius: ma.pressed ? 8 : 5
samples: 10
source: rect
color: "black"
Behavior on radius { PropertyAnimation { duration: 100 } }
}
}

Answer 2

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12
import QtGraphicalEffects 1.0
ApplicationWindow{
id: window
visible: true
width: 640
height: 480
title: qsTr("Hello World")
flags: Qt.Window | Qt.FramelessWindowHint
color: "#00000000"
Rectangle {
id: rect
anchors.fill: parent
anchors.margins: 10
radius: 5
}
DropShadow {
anchors.fill: rect
samples: 20
source: rect
color: "gray"
}
}

Answer 3

If you mean the drop shadow effect, that is not quite so.
We have no control over the WM decoration in Qt besides the frameless window flag you have just used. It is pretty much WM specific. Windows (TM) WM applies shadow effect to decorate windows, but this is a Windows (TM) choice. Also, you have just hinted that it should not decorate.