import QtQuick 2.5
import QtQuick.Window 2.2

Window {
    width: 300
    height: 300
    visible: true
    flags: Qt.FramelessWindowHint | Qt.Window
    color: "transparent";
id: w1;
   Rectangle{
       color: "green";
       anchors.fill: parent;
   }
}

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    width: 300
    height: 300
    visible: true
    flags: Qt.FramelessWindowHint | Qt.Window
    color: "transparent";
    id: w1;

    Rectangle{
        color: "green";
        anchors.fill: parent;
        Rectangle {
            width: 120
            height: 120

            x: parent.width - width / 2
            y: - height / 2
            color: "white"

            radius: 100
        }
    }
}