How to preserve strokes after canvas resized

[rock wang]

When the canvas resized, strokes will be clear. How to preserve them when adjust size of the canvas?
(the canvas fill the window and the window can be resized by user)

[ODБOï]

@rock-wang hi,
Could you plz show your code exemple ?
I binded my canvas size to my windows size and when i'm resizing everything is preserved for me

[rock wang]

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 1.5
import QtQuick.Layouts 1.3
import QtQuick.Controls.Styles.Desktop 1.0
import QtQuick.Extras 1.4

Window {
    visible: true
    width: 800
    height: 600
    //flags:Qt.FramelessWindowHint
    title: qsTr("优能视频客户端")

    ColumnLayout{
        id: mainLayout
        anchors.fill: parent
        Rectangle{
            width: 30
            height: 30
            color:'gray'
            Layout.alignment: Qt.AlignLeft | Qt.AlignTop
            Layout.fillWidth: true
            RowLayout {
                id: rowLayout
                anchors.fill: parent
                Image {
                    id: imgIcon
                    sourceSize.height: 16
                    sourceSize.width: 16
                    fillMode: Image.Stretch
                    Layout.alignment: Qt.AlignLeft | Qt.AlignVCenter
                    source: "qrc:/images/Logo.png"
                }
                Text {
                    text: "优能视频客户端"
                    Layout.fillWidth: true
                }

                Image {
                    id: imgMin
                    sourceSize.height: 16
                    sourceSize.width: 16
                    fillMode: Image.Stretch
                    Layout.alignment: Qt.AlignLeft | Qt.AlignVCenter
                    source: "images/minimizeNormal.png"
                }

                Image {
                    id: imgMax
                    sourceSize.height: 16
                    sourceSize.width: 16
                    fillMode: Image.Stretch
                    Layout.alignment: Qt.AlignLeft | Qt.AlignVCenter
                    source: "images/max_2.png"
                }

                Image {
                    id: imgClose
                    sourceSize.height: 16
                    sourceSize.width: 16
                    fillMode: Image.Stretch
                    Layout.alignment: Qt.AlignLeft | Qt.AlignVCenter
                    source: "images/closeNormal.png"
                }
            }
        }

        Canvas{
            property real lastX
            property real lastY
            id: canvas
            Layout.fillHeight: true
            Layout.fillWidth: true
            onPaint: {
                var ctx = this.getContext("2d")
                ctx.lineWidth = 5.0
                ctx.strokeStyle = 'red'
                ctx.beginPath()
                ctx.moveTo(lastX, lastY)
                lastX = area.mouseX
                lastY = area.mouseY
                ctx.lineTo(lastX, lastY)
                ctx.stroke()
            }
            MouseArea{
                id:area
                anchors.fill: parent
                onPressed: {
                    canvas.lastX = mouseX
                    canvas.lastY  =mouseY
                }
                onPositionChanged: {
                    canvas.requestPaint()
                }
            }
        }

    }
}