How to blur everything behind the Item

[yegender]

I am making a window manager like thing. Behind the active window everything is just dynamic they change their order and stuff and much going on. FastBlur can only blur the source Item. But here there are too many Source Items. How can I add blur behind every item. Here is my code :

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 1.15
import QtGraphicalEffects 1.15
import QtWayland.Compositor 1.15

Item {
    WaylandCompositor {
        id: waylandCompositor
        WaylandOutput {
            id: output
            compositor: waylandCompositor
            property ListModel shellSurfaces: ListModel {}
            function handleShellSurface(shellSurface) {
                shellSurfaces.append({
                                         shellSurface: shellSurface
                                     })
            }
            sizeFollowsWindow: true
            window: Window {
                width: 1024
                height: 760
                visible: true
                id:window
                Image{
                    id:wallpaper
                    anchors.fill: parent
                    fillMode: Image.PreserveAspectCrop
                    source:"file:///home/yegender/Pictures/ghost.png"
                }
                Repeater {
                    model: output.shellSurfaces
                    id:rept
                    Item{
                        anchors.fill: parent
                        ShaderEffectSource{
                            x:20
                            y:20
                            width:480
                            height:640
                            sourceRect: Qt.rect(x,y,width,height)
                            id:be
                            sourceItem:window
                        }
                        FastBlur{
                            source:be
                            radius:50
                            anchors.fill: be
                            Rectangle{
                                color:"white"
                                x:0
                                y:0
                                width:parent.width
                                height:30
                                Label{
                                    x:10
                                    y:(parent.height/2)-(height/2)
                                    text:modelData.toplevel.title
                                }
                                DragHandler{
                                    target:be
                                }
                            }
                            ShellSurfaceItem {
                                x:0
                                y:30
                                width:parent.width
                                height: parent.height-30
                                onWidthChanged: modelData.toplevel.sendConfigure(Qt.size(width,height),XdgSurface)
                                onHeightChanged: modelData.toplevel.sendConfigure(Qt.size(width,height),XdgSurface)
                                shellSurface: modelData
                                onSurfaceDestroyed: output.shellSurfaces.remove(index)
                            }
                        }

                    }
                }
            }
        }
        XdgShell {
            onToplevelCreated: {
                output.handleShellSurface(xdgSurface)
            }
        }
        XdgDecorationManagerV1 {
            preferredMode: XdgToplevel.ServerSideDecoration
        }
    }
}

It's outputing like this:

But I want blurring like this:

Thanks