一个小窍门是把你的对象+投影组合成一个单独的项目。当你让整个对象不可见的时候，你用一个虚拟的OpacityMask复制整个项目。然后，你把不透明度应用到OpacityMask上。
例如：

import QtQuick
import QtQuick.Controls
import Qt5Compat.GraphicalEffects

Page {
    background: Rectangle { color: "#ccc" }
    Frame {
        id: butterflyWithBoxShadow
        anchors.centerIn: parent
        visible: false
        padding: 15
        background: Item {
            Rectangle {
                anchors.fill: parent
                anchors.leftMargin: butterflyWithBoxShadow.padding * 2
                anchors.topMargin: butterflyWithBoxShadow.padding * 2
                color: "grey"
                opacity: 0.5
            }
        }
        Frame {
            id: frame
            padding: 1
            background: Rectangle {
                border.color: "blue"
                border.width: 1
                color: "#ffe"
            }            
            Image {
                id: butterfly
                fillMode: Image.PreserveAspectFit
                source: "https://www.arcgis.com/sharing/rest/content/items/185841a46dd1440d87e6fbf464af7849/data"
                smooth: true
            }
        }
    }
    OpacityMask {
        anchors.fill: butterflyWithBoxShadow
        source: butterflyWithBoxShadow
        invert: true
        opacity: slider.value
    }
    Frame {
        anchors.horizontalCenter: parent.horizontalCenter
        y: parent.height * 8 / 10
        background: Rectangle { }
        Slider {
            id: slider
            from: 0
            to: 1
            value: 0.8
        }
    }
}

你可以Try it Online!