Canvas -- 状态保存与恢复

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
   
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
    //Canvas是一个状态机，用save保存以前属性，restore弹出以前属性
    Canvas{
   
        id:mycanvas
        width: 200
        height: 200
        onPaint: {
   
            var ctx = getContext