main.qml

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.13
import QtQuick.Layouts 1.12
import QtQuick.Dialogs 1.3
import Drawing 1.0

ApplicationWindow {
    id: appWindow
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    property int pageWidth: 2000
    property int pageHeight: 2000

    Flickable {
        id: scrollView
        width: pageWidth
        height: pageHeight
        contentHeight: drawingCanvas.height
        DrawingCanvas {
            id: drawingCanvas
            width: parent.width
            height: pageHeight
            penColor: "black"
            penWidth: 20
            onWidthChanged: drawingCanvas.initiateBuffer()
            transformOrigin: Item.TopLeft
        }
    }

    MouseArea {
        anchors.fill: parent
        anchors.rightMargin: 20
        onPressed: drawingCanvas.penPressed(
                       Qt.point(mouseX, mouseY + scrollView.contentY))
        onPositionChanged: drawingCanvas.penMoved(
                               Qt.point(mouseX, mouseY + scrollView.contentY))
        onReleased: drawingCanvas.penReleased()
    }
}