qt qml scaling a image by touch event , image.y not correct when the second point was pressed

Question

Qt 5.12 quick ,i scaling a image by two fingers touch event, image's Y position not correct when second point where it on the frist point right and Top was pressed .

can't zoom normaly when point1.x and pint2.x very closely

my project file tree

Source
  main.cpp
Resource
  qml.qrc
    /
      2.png
      main.qml
      Root.qml
      RootForm.ui.qml

main.qml and main.cpp just display Root form, nothing special

RootForm.ui.qml

import QtQuick 2.4

Item {
    property int prePointX: 0
    property int curPointX: 0
    property int prePointY: 0
    property int curPointY: 0

    property int preDistanceX: 0
    property int curDistanceX: 0
    property int preDistanceY: 0
    property int curDistanceY: 0

    property int pngWidth: png1.width
    property int pngHeight: png1.height
    property alias touchArea: touchArea
    property alias png1: png1

    property alias p1: touchPoint1
    property alias p2: touchPoint2

    MultiPointTouchArea {
        id: touchArea
        touchPoints: [
            TouchPoint {
                id: touchPoint1
            },
            TouchPoint {
                id: touchPoint2
            }
        ]
        anchors.fill: parent
    }
    Image {
        id: png1
        source: "2.png"
        fillMode: Image.PreserveAspectFit
        width: 200
        height: 220
        x: parent.width / 2 - png1.width / 2
        y: parent.height / 2 - png1.height / 2
    }
}

Root.qml

import QtQuick 2.4

Item {
    property int prePointX: 0
    property int curPointX: 0
    property int prePointY: 0
    property int curPointY: 0

    property int preDistanceX: 0
    property int curDistanceX: 0
    property int preDistanceY: 0
    property int curDistanceY: 0

    property int pngWidth: png1.width
    property int pngHeight: png1.height
    property alias touchArea: touchArea
    property alias png1: png1

    property alias p1: touchPoint1
    property alias p2: touchPoint2

    MultiPointTouchArea {
        id: touchArea
        touchPoints: [
            TouchPoint {
                id: touchPoint1
            },
            TouchPoint {
                id: touchPoint2
            }
        ]
        anchors.fill: parent
    }
    Image {
        id: png1
        source: "2.png"
        fillMode: Image.PreserveAspectFit
        width: 200
        height: 220
        x: parent.width / 2 - png1.width / 2
        y: parent.height / 2 - png1.height / 2
    }
}

question from:https://stackoverflow.com/questions/65860281/qt-qml-scaling-a-image-by-touch-event-image-y-not-correct-when-the-second-poin

Answer 1

Waitting for answers