Graphics performance of listview and gridview is bad

import QtQuick 2.0
import QtQuick.Window 2.2

Window {
    visible: true
    Image {
        // Poor performance on 1920x1080 screen:
        //width: parent.width
        //height: parent.height
        // OK performance:
        width: 1024
        height: 512
        source: "backImg.jpg"
        cache: true
        smooth: false
    }

    GridView {
        id: grid
        anchors.fill: parent

        cellWidth: width / 3
        cellHeight: cellWidth
        model: 100;
        delegate: Rectangle {
            height: grid.cellHeight
            width: grid.cellWidth
            color: Qt.rgba(Math.random(), Math.random(), Math.random(), 1)
            opacity: 0.5
        }
    }
}

import QtQuick 2.8
import QtQuick.Window 2.2
import QtQuick.Controls 2.1

Window {
    visible: true
    id: root
    Image {
        id: backImage
        source: "preview_l.jpg"
        anchors.fill: parent
        fillMode: Image.PreserveAspectCrop
    }

    ListView{
        id: listView
        model: 100
        height: 200
        width: root.width
        orientation: ListView.Horizontal
        delegate: Rectangle {
            height: 200
            width: 200
            color: Qt.rgba(Math.random(), Math.random(), Math.random(), 1)
        }
    }
    Button {
        text: backImage.visible ? "Hide" : "Show"
        anchors.top: listView.bottom
        onClicked: {
            backImage.visible = !backImage.visible
        }
    }
}