Large fonts are not smooth with freetype

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.5

Window {
 visible: true
 width: 640
 height: 480
 title: qsTr("Hello World")
 Column {
 anchors.fill: parent
 Row {
 width: 640
 height: 440
 Column {
 width: 320
 height: 360
 Text {
 text: "0"
 font.pixelSize: slider.value
 renderType: Text.QtRendering
 }
 Text {
 text: "renderType: Text.QtRendering\nfont.pixelSize:"+slider.value
 font.pixelSize: 18
 renderType: Text.QtRendering
 }
 }
 Column {
 width: 320
 height: 360
 Text {
 text: "0"
 font.pixelSize: slider.value
 renderType: Text.NativeRendering
 }
 Text {
 text: "renderType: Text.NativeRendering\nfont.pixelSize:"+slider.value
 font.pixelSize: 18
 renderType: Text.NativeRendering
 }
 }
 }
 Slider{
 id: slider
 width: 640
 height: 40
 from: 120
 to: 360
 value: 240
 }
 }
}