前言

通过QML的QtGraphicalEffects模块实现的透明，可以使用FastBlur或GaussianBlur。

一、效果

二、代码

1.模块代码

//Rect_blur.qml
import QtQuick 2.0
import QtGraphicalEffects 1.14
Rectangle {
    property Item m_source
    property bool m_dragable:  true //未使用
    property color border_color: "transparent"
    property int border_radius: 10
    property int blur_radius: 32
    id:blur_rect
    width: 100
    height: 100
    radius: border_radius
    clip: true
    MouseArea {
         anchors.fill: parent
         drag.target: parent
         drag.axis:  Drag.XAndYAxis
     }

    Rectangle{
        id:blur_1
        anchors.fill: parent
        clip: true
        visible:false
        FastBlur{
            id:blur
            width: m_source.width
            height: m_source.height
            source:m_source
            x:-blur_rect.x
            y:-blur_rect.y
            radius: blur_radius
        }
    }

    Rectangle{//遮罩
        id:mask
        anchors.centerIn: parent
        width: parent.width+2//+2 去掉边缘遮罩层边缘漏色，不知道为啥??
        height: parent.height+2
        color: "red"
        radius: border_radius
        visible: false
    }

    OpacityMask {
            anchors.fill: mask
            source:blur_1
            maskSource:mask
    }

    Rectangle{//边框
        anchors.fill: parent
        border.color: border_color
        border.width: 1
        color: "transparent"
        radius: border_radius
    }
}

2.简单使用

代码如下（示例）：

Rect_blur{
    m_source: image_bg
    width: 100
    height: 100
 }

3.例子中的使用

//main.qml
import QtQuick 2.6
import QtQuick.Window 2.2
import QtQuick.Controls 2.12
import QtGraphicalEffects 1.14

Window {
    id:wind
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    
    Item {
        id:topcontent
        anchors.fill: parent
        //底部菜单之外的部分
        Item {
            id: content
            anchors.fill: parent
            z : 1
            Image {//背景图片
                id:image_bg
                anchors.fill: parent
                source: "qrc:/icon/nunzio-guerrera-x5mTFgOD6M8-unsplash.jpg"
            }
            Rect_blur{
                m_source: image_bg
                x:500; y:200
                width: 100; height: 100
                border_color: "red"
            }
            Rectangle{
                width: 100; height: 100
                x:100; y:200
                MouseArea {
                     anchors.fill: parent
                     drag.target: parent
                     drag.axis:  Drag.XAndYAxis
                 }
            }
        }

        //底部菜单
        Rect_blur{
            m_source: content
            height: 60
            width: parent.width-60
            z : 2
            anchors.bottom: parent.bottom
            anchors.bottomMargin: 20
            anchors.horizontalCenter: parent.horizontalCenter
            blur_radius: 40
            border_radius: 20
            ListView{
                anchors.fill: parent
                orientation: Qt.Horizontal
                model:10
                delegate: Button{
                    anchors.verticalCenter: parent.verticalCenter
                    icon.source:"qrc:/icon/icons8_lol_480px.png"
                    icon.color: "transparent"

                    background: Rectangle{
                        color: "transparent"
                    }
                    onClicked: {
                        popup.open()
                    }
                }
            }
        }
    }
    //弹出菜单
    Popup{
        id:popup
        anchors.centerIn: parent
        width: 200; height: 200
        modal:true; dim:true
        Text {
            anchors.centerIn: parent
            text: qsTr("Popup")
        }
        Overlay.modal: Rect_blur{
            m_source:topcontent
            blur_radius: 20
            opacity:0.6
        }
    }
}

总结

OpacityMask 的makesource使用rectangle时，如果设置rectangle圆角，圆角处会漏出rectangle的底色，目前是加宽了rectangle的大小解决